Home Made Bottom Heat for Seed Starting (or pet bed)

February 17th, 2009 by David LaFerney Leave a reply »
These tomatoe plants were grown under shop lights in only 4 weeks from planting the seeds!

I always had problems starting seeds in our plant room, but these tomato plants were grown under shop lights in only 4 weeks from planting the seeds!

These seedlings were planted only one week ago.  I used to wait weeks for germination that was spotty at best in my cool plant grow room.

These seedlings were planted only one week ago. I used to wait weeks for germination that was spotty at best in my cool plant grow room.

The answer was simple…
Recycling rope lights turn out to be a great way to make bottom heat for seed starting under lights.

Recycled rope lights turn out to be a great way to make bottom heat for seed starting under lights.

I built our “plant room” about 2 years ago – just a small well insulated room with a lot of windows and shop lights – and since then I’ve tried starting my own seeds with varying degrees of success.  The problem that I’ve had is that over night temperatures in the room routinely fall into the 50s which is fine for maintaining tender plants over the Winter, but makes seed germination spotty at best.  I knew that what I needed was bottom heat.

The thing is that retail bottom heat is expensive – I saw one “kit” at a local garden center that was big enough for 2 flats and was $79 – wow!  You can buy a lot of tomato plants for eighty bucks!  A low cost alternative had to be possible for a dedicated scrounger like myself.

Whatever I decided upon had to be:

  1. Safe – neither an electrical shock nor a fire hazard!
  2. Cheap
  3. Simple
  4. Big  enough to start all of our early Spring seeds.

Before proceeding – You the reader must agree that you will not hold the author or anyone associated with doorgarden.com responsible for your use of this information.  What you see being done in this article may not be safe (and probably isn’t), and could cause injury, death, destruction, mayhem, fire, dammage to your home, and prolong the economic downturn by preventing you from spending money and thereby stimulating the economy.  It might not even work.  In any event thou shalt not hold me responsible.  If you don’t agree with any of that then turn back now – don’t even look at the pictures.

After quite alot of thought I decided to use rope lights for the heat source – here’s what I did…

Rope lights going in over insulation board

Rope lights going in over insulation board

I already had a section of shelf in the plant room that was about 2 feet wide and 8 feet long that I wanted to use.  I put a 1/2 inch layer of styrofoam insulation board over the 1/2 inch OSB (chipboard) shelf and then loosely fastened the rope lights over that. This took 3 20′ lengths of rope light.  Note – after using this for a few days I would say that 2 strings of lights would be plenty for this size bench – I might rework mine to make that adjustment.

These rope lights are rated for exterior use and are double insulated.  They are safe for wet locations and direct contact with flammable materials like wood because they only get slightly warm.  Neither a shock nor fire hazard.  They were used at one time for outside lighting but hadn’t been used in a couple of years.  However it is probably always a good idea to use GFI protected outlets or plug bars anywhere that electricity and water come in close proximity.

The rope lights are fastened down using screws and wire ties that have holes for this purpose.

The rope lights are fastened down using screws and wire ties that have holes for this purpose.

zip ties with the holes for screws like this are extremely handy - look for them in the electrical wiring section of the home improvement store.

zip ties with the holes for screws like this are extremely handy - look for them in the electrical wiring section of the home improvement store.

Then I put in strips of 1 inch insulation board to act as spacers.  Looks kind of festive doesn’t it?

Then I topped that all off with a layer of 1/2 inch drywall…

Drywall going on top (I didnt fasten it in place at all)

Drywall going on top (I didn't fasten it in place at all)

Drywall is relatively fire resistant, and has good thermal properties so that the heat will be nice and even without hot and cold spots, but this kind isn’t at all water proof so I topped it all off with a left over sheet of vinyl flooring…

I already had this nice big scrap of vinyl floor, otherwise I could have used a scrap of vinyl or rubber roofing, pool liner, shower curtain, or plain old plastic sheet.

I already had this nice big scrap of vinyl floor, otherwise I could have used a scrap of vinyl or rubber roofing, pool liner, shower curtain, or plain old plastic sheet.

Here’s an end view showing the layers (except the vinyl floor)…

Most of the heat from the rope lights is directed by the insulation to go up through the seed starter.

Most of the heat from the rope lights is directed by the insulation to go up through the seed starter.

From the top you have – 1/2″  Drywall, rope lights and spacers made of 1″ EPS board, 1/2″ styrofoam, and 1/2″ wooden osb (chip board) on the bottom.  It’s all sitting on top of recycled 55 gallon drums full of water which act as thermal mass to moderated the temperature in the room.  You could probably use wood for all of the parts and it would be safe and work just fine, but I didn’t feel 100% comfortable doing that since I’m using the rope lights for something that they weren’t really designed for.  I did not close up the holes in the end.

Heres the system with fresh planted flats.

Here's the system with fresh planted flats.

The surface of the finished bench is just slightly warm to the touch, and the soil in the flats feels just like it would on a sunny day in May – should be just about right.  When I have actual results I’ll post some pictures.

In the planning stages I thought that an 8′ by 2′ starting area would be really roomy, but after my lovely wife commandeered 5 of the 8 slots for her flower starts I realized that it isn’t too big at all.  Barely adequate in fact.

  • The bottom heat stays on 24 hours a day.
  • The lights are on a timer which turns them on for about 17 hours a day.
  • When using florescent lights for plant starting the lights need to be very close to the soil / tops of the plants to keep them from getting leggy – even then they are not nearly as bright as the sun.
  • The air temperature in the plant room stays above 55° F.
  • Once the plants are a couple inches tall (probably about a month) I intend to move them out to the garden, greenhouse, or cold frame depending on the plant.

Note that I planned and built this project with an eye toward utilizing materials that I already had on hand – didn’t buy a single thing.  You should taylor your own projects similarly to use the materials, tools, skills, and spaces that you have available to you.  Some alternative ideas that I considered:

  • Light bulbs mounted under a shelf that would be like a shallow open bottomed box. – This could probably work all right but would be more likely to be a shock or fire hazard.
  • Recycling a water bed heater. – This would probably work, but I didn’t have a water bed heater.
  • Cement board tile underlayment instead of drywall.  – Good idea, but would have required the outlay of cash. I already had drywall scraps.
  • Bedding the rope lights in sand so that it would be completely surrounded by fire proof thermal mass. – This would probably work great, and I almost did it like that.
  • Bedding the rope lights in drywall joint compound or mortar for the same reasons of fire safety and thermal mass. – This would also probably work great, but if the rope lights died it would make it a huge job to replace them.  Also it would be a big messy job to put it together.
  • Using a small space heater under an open bottomed shelf. – Everything would have to be made out of fire proof material for this to be safe.
  • A lower level of shop lights to bottom heat an upper level of seedlings. – This would be a likely shock hazzard because of excess water running down onto the lights, and you wouldn’t be able to use the bottom heat 24 hours a day.
  • If / when electric heat was not an option heat could be supplied by a layer of hot compost under a cold frame – This is called a hot bed.

After running this for a few days it has occured to me that something like this would make a really nice heated dog or cat bed.  Just a thought.

Update: I planted a variety of seeds one week ago tomorrow, and almost everything has already come up including some stevia seeds that are supposed to be hard / slow to germinate.  This works.

Update 2: A couple of things that I would do different and will probably change – My bottom heat covers an area about 8′ long by 2 feet wide which is great, but it would be getter if I could independantly turn it on and off in 4 foot sections, for when I’m not using all of the area. By the way, after about a month of use I’m astounded by how well this works!

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  1. Ann says:

    Fantastic idea with the heated bed. We have a big poly greenhouse but it is expensive to run when there is snow outside so I am starting my flowers and peppers inside. I too wanted cheap. I don’t know if this is a fire hazard so PLEASE don’t copy me unless you want to take the risk. I have an old electric blanket that we don’t use so it folded it up on some melamine board I had, covered it with towels and put my flats directly on it. I am doing my best not to get anything wet. Because of it being a blanket I expect that code would make it fairly safe with moisture.
    Next year I am going to take the heating line out of the bed and arrange it on a board, much like yours. I stick a thermometer in between the layers, I find it turns off when it gets too warm so I need to check it once in a while. I planted my waves 3 days ago and already have sprouts. Wow. Just as an aside, I read that mold ect… Is a problem starting plants. I am a big advocate of peroxide, both 35% food grade as well as the first aid bottle stuff. I am adding generous amounts of the 3% to my water to avoid mold. Wel will see if it works. Have a good spring everyone.

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  3. Jay says:

    Whatever I decided upon had to be:
    1. Safe – neither an electrical shock nor a fire hazard!
    2. Cheap
    3. Simple
    4. Big enough to start all of our early Spring seeds.

    ……What you see being done in this article may not be safe (and probably isn’t), and could cause injury, death, destruction, mayhem, fire…….

    WOW, seriously…

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    hi David,does this cause an increase in the electric bill? if yes by how much? thanks and have a good day.

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  12. Chris says:

    Hi David,

    Just read your very interesting article and have determined to try it for myself, but have a couple of questions. How necessary are the 55 gallon drums of water for acting as a thermal mass, and do you think this would work in an unheated garage or would I need to set it up in the house?


  13. i believe you are losing heating with your set up. if you was to use pvc pipe in short sections, 1″ tall would be plenty, as spacers between bottom and top, the lights would warm a greater area. you can use nuts and bolts through the pvc pipe to hold the whole thing together. this way you could also close up around the lit areas and leave only small vent holes around to keep the space from getting too warm. in the illustration, it looked to me, like you laid the lights and made channels, i am eliminating the channels to an open room type of idea. this way the heat is evenly distributed and there is no dead spots.

  14. GW says:

    Have you had any issues with the rope lights burning out and overheating? I built this same type mat 2 years ago and just looked at the rope lights after two seasons and some of them had got hot enough to scorch the rope.

    • Emily says:

      Have a new system, several sections of my rope lights burned out in short order–I think they needed more breathing room than I gave them. Have bumped up the top platform to increase circulation, continuing to heat with the remaining lights. But it certainly speeds up germination!

  15. nokomis says:

    This sounds like a great idea for an outdoor project of mine. I want to start a compost project in 45-gal containers, and I’d like extra heat to bring them up to 70F where the thermophilic microbes can start working. A friend suggested grouping four containers together, putting some heat source between the containers, and insulating around the sides and top of the whole thing. Outdoor rope and other holiday outdoor lights might be just right for this outdoor application.

    This is done in Australia where the bins are called ‘wheelie bins’, but I think the weather is hotter there so I may need to add heat to get it started. (I’m in Seattle.)

    • Emily says:

      I think you may be misinformed–it’s the bacteria themselves that CREATE the heat, not you. We in Master Composters refer to it as an “enzymatic feeding frenzy.” What you have to do is give them optimal conditions: a 30:1 carbon/nitrogen ratio in your feedstock, 50% hydration (the proverbial wrung out sponge), air (periodic turning) and mass (a minimum cubic yard). If those little microbes have those elements in balance, they’ll go to work for you. I live in Vermont, get finished compost in 6 weeks this way in summer, but it’s like a pet, I have to give it food and attention.

  16. Homesteader says:

    I was out of town and sent your link to my hubby. He found rope lighting at Lowe’s after Christmas for half-price. This system should work great in my basement seed starting area. I struggled last year with proper bottom heating in the cool basement, and about had a heart attack when I priced heat pads from Parks and Burpee. Now my hundreds of plants will thank you for taking the time to log and post your project. My special thanks to you.

  17. Can’t wait to give this info to my husband, I think we even have most if not all the materials around. Thank you for sharing your experience with everyone.

  18. Tim says:

    I found a video on youtube that gave credit to you for this design so I had to visit. I am thinking I will try to make at least one for the spring to help my seedling along. Thanks for posting the concept and as long as I don’t lose the link I’ll come back to report on how I did as well.

  19. Kimberly says:

    I have a solar powered led rope light. Do you think it would produce enough heat for this purpose?

  20. Terry says:

    I’ve used an old waterbed heater as a seed starting mat. It works great! Be sure to put the temp probe ON THE MAT as someone mentioned above! I put it on top of the soil. That worked until my soil got too dry to conduct heat properly. The heater kept heating, but the change didn’t register, so it heated some more. It was a little scary finding my flat melted one morning! I started over with a different flat, and the probe on the mat. I never had any more problem.

  21. Cody says:

    I personally use fish tank heaters for the same purpose – simply place in a large tray covered with plenty of water and place the plants on top. Since all of them have temperature controls in the range you want, it is very easy to get a consistent temperature, it won’t wast electricity when it is already warm enough. A 200 watt unit sells for about $16 on Amazon. Just make sure to keep the water topped off!

  22. Suzanne says:

    I’m thinking maybe you could have tilted the shelf slightly, maybe have the back 3/4″ higher, just enough to make any excess water drain forward into a makeshift ‘gutter’ made from metal scraps, or even something like a thin mobile home guttering. have the water run to one end into a catch bucket. great project! I’m assuming that’s a cement floor, those barrels would weigh about 1600 lbs!cda2

    • Norm says:

      Great idea! After I built my propagation table last year, I added an “A” frame and covered it with plastic to help hold in the moisture and heat because otherwise even with bottom heat my garage is a tad cool. One thing I am dealing with now is condensation accumulating, pooling, and running out where I don’t want it. Your suggestion is a simple and clever solution. Thanks!

  23. LadySparkle says:

    Thank you for this. I try to over winter many plants that thrive out doors every year and I think my house is just kept too chilly. These will serve two functions for me. Maintaining my house plants and starting seedlings next spring.

  24. Shanda says:

    Hi there. I’m completely new to indoor seed starting and I was just curious how much this sort of set-up raises your electric bill? I’m assuming it’s probably worth it or you wouldn’t be doing it, right? Quite a clever idea!

    • Norm says:

      Typically, non-LED rope light runs 5 to 6 watts per foot per hour. So in the example posted with 3, 20′ rope lights at 5.5 watts (per hour) = 60*5.5 or 330 watts. This * 17 hours = about 5,610 watts usage per day. This is about = to leaving 4, 60 watt light bulbs on all day. Companies charge by the kilowatt used (1,000 watts). So, the energy company will charge you for 5,610/1000=5.61 kWh. Locally we are charged about $.085 per kWh {Note, that is NOT 8.5 cents….it is .085 cents}. So 5.61*$.085=approx 48 cents per day or $14.50 per month or thereabouts. Yeah; it’s worth it to me to have those wonderful veggies and flowers next spring and summer!!! And a lot cheaper than the local nursery per plant!

      • Shanda says:

        Thanks for breaking it down for me. You’re right, considering the cost of plants … not bad at all. If I can get my husband on board, I want to do this. I’m sick of planting the same ole boring varieties every year. I’d like to grow some new varieties that the nurseries don’t sell. Thanks for the response!

  25. davidw says:

    Hi, Thanks for the great post.
    I am wondering what is the day and night temperature are needed, caused I had tried to start seed in my basement but didn’t have much good result, where the temperature is 19 celcius consistent.

    • Norm says:

      Hi! I built this system and I am very happy with it (I have some comments here). To answer your question, you need to know the germination requirements of the seeds you are planting. While growing plants/seedlings may like a “daytime/nightime” range of temps, seeds prefer (in general) a consistent temperature, though they will germinate within a range. For example, Chives need a temp of about 60 to germinate. Oregano likes 70 degrees. Here is a chart from the U of Alabama and Auburn extension divisions on vegetable seed germination temps (F).

      Sorry I couldn’t get the table to show here like a table, but it should be easy to figure out.

      Vegetable/ Min temp/ Optimum Range/ Optimum temp/ Max temp
      (°F) Range (°F) (°F) (°F)
      Asparagus 50 60-85 75 95
      Bean 60 60-85 80 95
      Bean, Lima 60 65-85 85 85
      Beet 40 50-85 85 85
      Cabbage 40 45-95 85 100
      Carrot 40 45-85 80 95
      Cauliflower 40 45-85 80 100
      Celery 40 60-70 70 85
      Chard, Swiss 40 50-85 85 95
      Corn 50 60-95 95 105
      Cucumber 60 60-95 95 105
      Eggplant 60 75-90 85 95
      Lettuce 35 40-80 75 85
      Muskmelon 60 75-95 90 100
      Okra 60 70-95 95 105
      Onion 35 50-95 75 95
      Parsley 40 50-85 75 90
      Parsnip 35 50-70 65 85
      Pea 40 40-75 75 85
      Pepper 60 65-95 85 95
      Pumpkin 60 70-90 90 100
      Radish 40 45-90 85 95
      Spinach 35 45-75 70 85
      Squash 60 70-95 95 100
      Tomato 50 70-95 85 95
      Turnip 40 60-105 85 105
      Watermelon 60 70-95 95 105,

  26. Chaya says:


    Thanks so much for posting your ingenious heating solution! I’ve shamelessly copied it for my setup and I’m experiencing great results.

    I spent $75 on the materials (didn’t have much laying around) and it’s supplying heat for 8 trays. The local nursery’s price for a one tray heat mat setup was $30. pshaw!

  27. Mick says:

    Hey David, Great idea! I just built a 36′ greenhouse here in Maine. gets real warm during the day. I have 19 flats around my woodstove and 19 more on a 6′ by 8′ 2 x4 tray rack, (It took 12 2 x4’s). my seedlings are 4- 7 days old with some around 4″. I want to move some out to my unheated greenhouse. I have 5 big tables in there. I was thinking of making each table a mini greenhouse inside a greenhouse. I have water heating up during the day in 5 gallon buckets with other heat sinks under the tables than plan to cover with 2 layers of 6 mil and 1 layer of an insulating material. I was thinking of a simple heat lamp, lightbulb or small electric heater under the table to keep temp up to 55 – 60. We are still going down to 28 – 32 every nite. I’m new to starting inside this despite the fact I just planted a few thousand seeds. Any thoughts?

    • David LaFerney says:

      It sounds to me like you are on the right track. Depending on what kind of plants you are working with they may not need much supplemental heat once they emerge – some do of course.

  28. Jim Donovan says:

    Just wanted to comment on your statement that GFI protective devices need a ground lug on the cord to be functional. This is not true. In fact GFI breakers can be used in old homes (pre 1960 vintage) that have receptacles not equipped with ground receptacles. The GFI device senses the current going out on the hot wire and if it is not within 5-10 milli-amps of the current returning on the neutral wire, the breaker trips. This protects people from the fatal results of very small currents passing through the body. These small currents would never be detected by a non-GFI breaker. It would be highly advisable for your installation to make use of one of these devices in the chance that a hot wire could become exposed to a persons contact, and, especially with drums full of water being an excellent source of ground path for the stray current path back to it’s source, the panelboard or fuse box.

    • David LaFerney says:

      I certainly agree that GFI protection is always a good idea – and I will edit the article to reflect that.

  29. Norm says:

    I am amazed! I finally got things adjusted with your help and advise. I seeded several varieties of peppers. They came up about 50% faster than normal. And, I had about 98% germination of all the varieties…a first for me! I am blown away by this. IT WORKS GREAT!!!

  30. Steve says:

    WOW! What an awesome idea! I never would have thought of using rope lights for that. Dang, now I have Another project added to my list! LOL! Thanks a lot for sharing this. Got several friends I’m going to have to send over here as well.

  31. Travis says:

    I just saw rope lights on sale right after christmas at walgreens for 50%off. I wish I got them, but I did get New LED’s X-mas lights for cheap…Shop around next year for this idea…

  32. Norm says:

    Help? O.K. So, I built a similar set up. Except that mine is on a strong folding table. Essentially I built a box and put it on the top of the table. Inside dimensions are about 5′ x 2′. I built the box out of scrap 2×4’s. The bottom is 3/4 plywood…also some scrap I had. On the inside of the box (bottom) I put down a 3/8″ sheet of foamcore (the kind of stuff you insulate garage doors with). I discovered 1 x 2’s are 3/4 inch…not 1″, and this makes them a fraction of an inch thicker than the ropelights. So I used some 1 x 2’s to create channels and to provide support for the drywall which sits on it just above the lights. Since my box is smaller than yours, and based on your thought that you would only use 2 strands for yours in the future, I bought 1 18′ ropelight from Home Depot. I placed it around the box like you did yours and then set a 3/8″ drywall over it all. I covered that with poly, then put a test flat with media for seeds on the top of the poly. I put a cover on the flat that came with it for starting seeds. Looked good!

    We had a cold snap and my garage is about 53 degrees (normally 60 or more). After a day of running the setup I decided to check it all out. My garage was 55 degrees. The inside box (lights area) was only 60 degrees. The media in the flat was only 57 degrees. Certainly nowhere near mid-May sunny day temps! When I felt the lights (which are a commercial duty rope light), they felt warm. The plastic surrounding them felt pretty soft.

    Oh…did I mention my wife is afraid I am going to start a fire? ;)

    Here are my questions: when you touch or feel your rope lights, I will assume they feel warm…is the covering a little soft? If I double the lights in the box, would I expect it to raise the temperature only another 2 or 3 degrees…or is it more like a log thing and the heat will be greater? Why isn’t more heat transferring through the drywall? I thought about covering the lights with sand, but an electrician said he wouldn’t do that because they could get too warm…he wasn’t real comfortable with them being in an enclosed box. What if I set the flats on the 1 x 2’s (essentially on the lights) and bypassed the 3/8″ drywall step….would that deliver more heat to the flat/media/soil? I believe if I have two strands instead of just one, the heat would be uniform? If any of this confuses you, contact me and I will send you photos. :)

    • David LaFerney says:

      How much time did you give it? They don’t put off a lot of heat (which is good) so it takes time for it to all get warmed up – a day or two anyway. Does the garage get COLD? As in 30-40 degrees? If so, you might need to use more lights per square ft – you can see from the pictures about how many mine have. Do you also have lights close to the soil? I do. Do you have plastic “greenhouses” over the soil? I do, and that helps to keep the heat in until the seeds germinate. You might just be over thinking it – give it a chance as long as the soil isn’t cold you might be surprised.

      • Norm says:

        I gave it enough time, but you were right…not enough lights. I added a string and the temp jumped up about 10 degrees. I don’t have lights over the soil…I need to add that. I added a plastic “tent”….made an “A” frame to fit the plastic over and the temp went up another 5 degrees. Thanks for the help!

  33. Pobept says:

    What a great idea. Recycle what you have, inexpensive if starting from scratch and effective.
    I will build me one very soon. A bit smaller but I don’t have the space for one as large as you constructed.

  34. Norm says:

    Great ideas for bottom heat! I knew there had to be a better solution than $50 pads from the garden center! Thanks! ….oh…do you know how warm the medium actually gets with your method? Have you stuck a thermometer in it? I also liked your follow up to build it in several sections so you can just use the ones you need and not the whole thing.

    • David LaFerney says:

      I never have checked the temperature – kind of silly I guess, but it feels about like the soil does on a warm sunny day. It really works.

    • Tom says:

      I made one of these too and wrote it up on my blog.

      I bought controllers from hydro farm About $50 with a temperature probe and a digital readout/setting for temperature setpoint.

      My basement is about 67 degrees and my seed mats can only get up to 80 or so.

      My tomatoes all geminate. Eggplant mostly does. Celery is a bit harder, but it goes.

  35. shirley says:

    I am using the rope lights in a 4 shelf indoor greenhouse…but, since I keep the lights on….I have lighting in the greenhouse. I can see moisture on the walls of the plastic. When should I remove the plants from inside the greenhouse? They seem to be doing very good. I just started this week. I used your idea…I just read about the board over the lights to have balanced heat…I am going to do that …. thanks

  36. thedeckguy says:

    Went to Big Lots, bought 4 (10 each) peat moss starter kits for seeds, the type you add warm water to & they expand, added my seeds from the Dollar Tree (4 packs for $1) & then put them on top of monitor heater by a window that gets indirect sun. Labeled them & put dates so I would know when to expect germination. WOW !! Was I surprised when after 3 days my squash, tomatoes & basil had sprouted & are now about 1-4 inches. Just waiting on my jalapenos & green peppers. Shouldn’t be too much longer. Now I have to go back to Big Lots. Got plenty of seeds for $6. What a good problem to have.

  37. Sharon says:

    Brilliant! I used rope lites to light my plate rack around my dining room so I should have thought of it myself!

    I have a garden window that I uselessly placed in my kitchen in the NE corner of my house. Good for the house design if I could just rotate the house. Always wanted to grow herbs so I’m adding a grow light and using your plan. Thanks for sharing!!

  38. Sandra K says:

    What a great idea! The heating mats are expensive and way too small to do any good. I’ m already doing up some plans. I hope you don’t mind if I print out the directions to show my teenage daughter. She is the engineer in the family. Last year I used old Christmas lights along the bottom third of my PVC Gable greenhouse. [My daughter did most of the greenhouse construction 3 years ago.] The greenhouse stayed above freezing, and cost a lot less to heat. A light snow even melted off. It really made for some cool pictures; looked like a giant night light. I’m going right out to find some rope lights and have my daughter help me start putting it together. I just have to make sure they’re not the new LED lights. LED lights don’t heat up. I am excited to try this. I think it will work great in the greenhouse. With floating row covers to help keep the soil warm I think I can get the seeds to sprout early. Its March and I haven’t even started planting. I am so behind.

  39. Jan M. says:

    Tho there is lots of 411 for using fluorescent lights, I cannot have them with the setup I have & am using a 65 watt incandescent grow light. It is about 17 – 18″ from the plastic “roof” of the Jiffy greenhouse. Does anyone know the correct distance it should be? The seeds germinated in record time, so I don’t know if this distance is too close while they continue growing.

  40. Jan M. says:

    I cannot believe my eyes. I made my own heated seed bed & planted moss rose & alyssum seeds not 40 hours ago, and they’re coming up already. They’re in Jiffy seed pots, so I’m not mistaking weeds for flowers. The only difference in mine is that I used cup hooks to hold the rope lights in place. And the only reason I found this site is that my store-bought cute little greenhouse isn’t working. I bet I didn’t get 3 months of use from it, so I got mad & went on line to see if I could make my own. Using rope lights is a genius idea. I should add that I forgot to turn the grow light off last nite & was afraid I cooked the soil, but it’s OK. I’m going to have the light on a timer for sure from now on.

    • David LaFerney says:

      It’s amazing what a difference the bottom heat makes isn’t it? But, don’t write off the greenhouse just yet – You just need to figure out what it works for for you.

  41. Tara says:

    What a great idea! I happen to have extra rope lights and sand. I too thought of electric heat pads, but cautious for safety reasons. Thanks so much!

  42. nancy says:

    what about an electric blanket or mattress pad.

  43. Ken Wells says:

    Your experiments are great and very useful. Our site is not published yet.
    We put you on favourites.

  44. Frank Dunn says:

    I truly injoyed your bottom heat artical.
    I was checking the prices for heaters,and
    they are very high,so I( am going to try your idea.thank you for your post.
    Frank Dunn Indianapolis In.

  45. terry says:

    hi i need some help i have read some of the letters and everyone has a lot more wits at seed starting then me but every time i get my plants started and take the clear lid off in about three days my plants start dieing off i do know if i am leaveing the top on long enought or my lights aren’t close enought this makes three times now that it has happened does any one have any pointers thanks terry

  46. Susan Galyon says:

    Your site is so full of info. Thank you for posting. We just bought the rest of the stuff for your hoop house construction and I found your article about sprouting seeds. I use a water-bed heater and it works great. With the built-in thermostat, I just dial the temp and set the flats on top. I have also at various times used a heating pad and an electric blanket, both of which were safe to launder. Both also have thermostats though not as accurate as the water bed heater. I love your idea of using insulation board and will adopt it from you. Thank you for realizing imitation is the sincerest form of flattery and sharing your great ideas with the rest of us gardeners.

  47. Naseer says:

    I’m a huge fan of this blog–thank you for these great writeups! We are located in the Hudson Valley of New York, where the official outdoor planting day is around mid-May. And unfortunately, we haven’t (yet) ventured into building a greenhouse, but we’re looking into finding some glass to build cold frames based on your instructions.

    My only concern is what happens if we see too much success from this lighting and bottom-warming setup? That is, if the plants are a few inches tall in a month, will we be able to sustain them indoors for another 2 months without incurring harm? We’re willing to hang the lights from a hook like another reader suggested, so we should be able to light them even if they grow taller. Any advice would be greatly appreciated.

    • David LaFerney says:

      Naseer, You are absolutely correct in that you need to plan ahead for what you are going to do with those little plants once they get bigger.

      Right now – in the middle of February – I have mostly plants that are in the cabbage family, and onions growing under my lights. Those can go out into the greenhouse or cold frame as soon as they are big enough to transplant because they tolerate cold weather.

      In early March I will be starting tomatoes, peppers and other warm season plants that will go into the garden after our last frost date in mid-late April. You need to time your planting based upon your local norms. If you don’t know what the dates are for various crops in your area I suggest that you ask the people in a local farm supply store or co-op. If that isn’t an option you can also get a pretty good idea here – http://www.ncdc.noaa.gov/oa/climate/freezefrost/frostfreemaps.html

      Great question. Good luck.

  48. glenn powers says:

    did those rope lights have leds?

    • I don’t really know, but I don’t think so. They were less than $20 a set several years ago when they were bought for outdoor lighting. If you feel the lights when they are on they just barely feel warm. I’m using them for the second year right now, and I have bok choi coming up after only 3 days. That’s hard to beat.

  49. Tom says:

    I just made 2 of them this weekend. 2′ by 4′. I have a wire rack on wheels with my lights on it. I’ve added a shower drain to garden hose to my setup.

    My local pet shops didn’t have the temperature regulator so I ordered a seedling mat regulator. They have a sensor you put in the soil and an outlet. They claim to work with any mat and can handle “up to 10 mats’ or (I think) 1000 watts.

  50. kathi dunphy says:

    Great idea! I built something similar with leftover tiles and a light bulb to freeze-proof my chicken waterer. Also if anyone is interested a combination greenhouse/chicken house. Various construction posts on my blog

  51. Evelyn says:

    You can get an adjustable thermostat at PetSmart that you can plug the whole setup into it is made so the sensor can be placed into the setup.

    You will find them in the reptile heater section.

  52. Lee in Iowa says:

    I’ve used shop lights on timers (16 hrs / day) for years with great success in raising my own seedlings. Hang the lights on chains w/ s-hooks so you can move them up gradually. If you don’t want to do quite so much work & you only start a few flats of seedlings, setting them on top of your refrigerator works well. (They don’t need a lot of light yet, but toss a lightweight drycleaners bag over each flat to keep the moisture in.) Oh, and don’t buy “grow lights” for your fixtures; these days, if you read the packages carefully, you’ll find they’re just regular light bulbs tinted some clever color like green or blue!

  53. Mike Eaton says:

    this did not work for me

  54. Erin says:

    David, Again, another fantastic idea (I may never leave your site this morning…I keep sending links to my husband at work). Question…how many hours a day were you keeping your above plant lights on? We did our first attempt at starting our crops from seeds last spring and it was dismal (the great aphid invasion wiped out anything that started, too). I think your bottom heat solution sounds fabulous.

    • 12-14 hours more or less of on time seems to work pretty well for most things. As a general rule you don’t want to do 24 hour light – it messes with the natural rhythms of some plants just like it does with people. You want to simulate Spring-Summer daylight.

  55. Danny Sleeper says:

    I am really excited about your sight,bottom heating is something I have never considered because, like you, money is an issue but this sounds like the way to go.Seeing as how it is almost july and a little late for this I will have time to get everything together. I am in eastern North Carolina and have a pretty good growing season and this will make a good early start

    • Planning well ahead is the way to tackle a project like this – if you don’t wait until the last minute you have a good chance of getting all of the materials for cheap or even free. Just keep your eyes open for what you will need – and grab them whenever you get the chance.
      Good luck – Winter will roll around again before you know it.

  56. gin maxwell says:

    A question for you. How long do you keep the bottom heat going? My plants are getting bigger, and now I am unsure of whether they need the heat any longer. Soon I will need the set up for starting my tomatoes, so I’d like to boot the earlier stuff out of the warm bed. My entire set up is inside the house so it is basically warm where they are.

    • David LaFerney says:

      Your guess is as good as mine. I’m having the same issue – After only four weeks from seed all of my tomatoes were about the size that you usually see for sale.
      I’d say that if you need the space go ahead and move out whatever is already established to make room for the new. It might not be optimal, but what else are you going to do?
      Here in middle TN it’s warm enough to move most anything out to the hoop house – which is starting to fill up too I might add.

      • gin maxwell says:

        I decided to leave the peppers and eggplants with cozy warm toes, but the cabbage, broccoli and Brussels sprouts got a new home by the window. It was warm enough today in eastern Nebraska to do some real digging in the garden, ah-h, what great fun.

      • CondoGarden says:

        As a suggestion, once you get 2-4 sets of true leaves (not counting the first two “seed” leaves) take them off of the heat. Let them get used to normal conditions. At least a few days to a week before planting, try to put them outdoors; in a coldframe would be great.

        The reason for this is, you don’t want your seedlings to go from warm, comfy-cozy indoors to the cold, harsh, barely-past-the-last-day-of-frost outside without some conditioning. This is what’s know as “hardening-off.”

  57. gin maxwell says:

    This heat thing really works. I had broccoli, cabbage seed up in just one day. Amazing. Even the tricky to start Thai long green eggplant is beginning to emerge. This is a great experiment.

    • I know, I’ve had basil sit there for 1-2 weeks and then just get 50% germination before. With this set up nearly 100% of my 3 varieties of basil have come up in about 2 days. Stevia is supposed to be really hard to start from seed, but I’ve gotten about 50% germination of that in around 1 week. This is the key to indoor seed starting for me.

  58. Bill Buron says:

    The only problem is that the building needs to be heated and the ropelight is not on a thermostat so I think it may be difficult to control the heat on the bottom of the plants.

    Thanks again Bill

    • David LaFerney says:

      I don’t know Bill – with your cold frame inside of a greenhouse arrangement I suspect they would give plenty of heat even in an unheated greenhouse. Nonetheless, I’ve been kicking around ideas for making a thermostatically controlled plug bar that could be used for this, or an incubator, or whatever you plugged into it. My setup works great so far, but as the weather warms up a bit more control might be called for.

      • wilma travaille says:

        wondering if you have any pics of the water mattress with waterbed heater inside your greenhouse? Thanx

  59. gin maxwell says:

    I was glad to see this setup with rope lights. I just put a 6′ rope light in a bed of sand today and have it plugged in to test. It is attached to a wire mesh base and in a shallow tote. A second tote will fit on top the sand. My only worry was the warning on the box of lights that said not to cover or use at temps above 70?. That’s why I was looking for others who had used this type of bottom warmer.

    • David LaFerney says:

      All I can say is so far so good in my case. The lights might not last very long if they are over heated, and they might not be safe. Seriously you shouldn’t take any chances with fire safety. I’m sold on bottom heat though, I am getting the best results by far that I have ever achieved starting seeds under lights – a very fast, high germination rate with everything that I’ve planted so far.

      • gin maxwell says:

        Had an electrician friend take a look and he didn’t seem to think it would be any problem. He said it anything they’d just burn out. I haven’t started any seeds yet, but Sunday is my day for eggplant and peppers. Broccoli to follow soon. This will be a great adventure.

  60. Dave says:

    Very interesting! I thought of using pipe heating cords to do something like this. Have you measured the surface temperature?

    • David LaFerney says:

      Just now the surface temp is in the mid to upper 90s with soil temps in the mid 80s. The air temp in the room right now is 80 because of solar gain – early this morning it was 60. I can actually see impatiens that have emerged since I finished this project yesterday after noon. I’ll check the temperatures again tonight after it cools off and post the results here. By the way, one advantage of the water bed heater option would be that they have a thermostat and temp probe already built in. I’ve seen them at junk stores for $5.

      • Duane Keys says:

        Any more temperature results? Looks like a great idea!

        • David LaFerney says:

          I just checked and the soil temp at 9:30 pm is 80-90 F – probably a bit higher than really needed – air temp is 70. But, I have stuff coming up here and there after only 3 days, and some seeds that I’m checking for germination rate that are sitting right on the warm bench are sprouting about as expected. I’ll probably spread out the rope light that I’m using to heat the rest of the bench too, but I’m pretty happy with the results already.

          • Guess I’m a little late to the party but was wondering why all the super caution about water getting on rope light. maybe I’m missing something and I surely don’t want to downplay the seriousness of electricity but aren’t rope lights made to withstand the rain and snow outdoors? I wouldn’t want them sitting in water but will drips and drabs matter?

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