Starting Seeds Indoors Under Lights

February 8th, 2010 by David LaFerney Leave a reply »
seedlings growing under lights

Seedlings growing under lights

I started some seeds today in my “plant work room” and I thought you might be interested.  I start seeds in regular plastic nursery trays that I get from a local greenhouse – and that I save from store-bought plants.  I do recycle my plant containers from year to year –  If you reuse containers like this you really should wash them thoroughly in a weak bleach solution and dry them in the sun before storing them away for reuse.  Or so I’ve heard – I might try that some day.

just planted flat

just planted flat

This year I’m planting in commercial soil mix, because I just don’t have any compost that is ready right now to make into home made potting soil.  Anyway, fill your containers with soil and plant your seeds at the  recommended depth.  Most of what I planted today is in the cabbage family, and needs to be about 1/2 inch deep.  I just use a finger to poke holes about that deep, drop 2-3 seeds into each one and then sprinkle with more soil to cover.  I’m using pretty small divisions – 72 plants per tray – because I plan to plant out these cold season plants under row covers or in the greenhouse as soon as they are big enough to handle.  If I thought that I would have to hold them for a while I would probably start them in larger divisions to begin with.

BTW, I am also test germinating some seeds that I saved last year – by planting 10 seeds per container to see how many come up.  Assuming that some of them germinate I can just multiply the number of seedlings by 10 to get the success rate as a percentage.  Other than using 10 seeds per container they are done exactly the same way as everything else.

watering a flat with a spray bottle

Using a spray bottle to water the planted trays gives good control.

I’ve found that the least messy way for me to water trays is by misting with a spray bottle – every other method that I’ve used results in muddy water running everywhere and only a little soaking in.  Check soil moisture every day until you’re sure that it has stabilized where you want it – moist, but not dripping wet.

Note that you need to label your trays – I use recycled pieces of plastic mini blinds.

plastic seed starting chamber

A plastic seed starting chamber like this is very handy, but not absolutely required.  You will have to remove it soon after your plants emerge, but until then it helps to keep the soil evenly moist and the air warm and humid.  If you don’t have one of these just lay a sheet of plastic right on top until you see plants starting to emerge.

Then cover with one of these plastic domes if you have one.  If you don’t have one of these you can simply drape a piece of saran wrap over the tray, but if you do that you will have to remove it as soon as you see plants emerging from the soil.  The cover holds the moisture in so that you shouldn’t have to water again until it’s removed.

the grow light setup

My simple grow light setup uses regular 4′ shop lights and bulbs – not expensive “grow” lights.

I use plain old 40 watt flourescent shop lights to start my plants indoors and it works great.  As you can see the fixtures are just sitting on top of props that I have made out of one by six scraps, but you can use whatever you have.  You want the lights to be as close to the plant trays as is practical or your plants will grow tall and leggy.   Now that compact florescent lights are widely available you could also use those in any lamp fixture that you have.  You can easily get CFLs which are equivalent to  a 100 watt incandescent light  – should be great for a smaller operation.

Last year I built a very simple bottom heat system which has made a tremendous improvement in my success rate for starting all kinds of seeds.   If you don’t have bottom heat, then try to keep the soil as warm as possible 24 hours a day.  On top of a refrigerator or an upright freezer is a good place or on a shelf right over your water heater or a heat appliance.  The regular average room temperature of your house is probably not warm enough for best results.  The lights also won’t really work to keep the soil warm because they won’t be on 24 hours a day.  If you look at this planting soil temperature chart you will see that most plants want the soil temp to be around 80 degrees Fahrenheit for best germination.  If at all possible use some form of bottom heat.

light timer

A simple analog light timer is all y0u need for starting your own plants, but you need one that is big enough to handle the load of all of the lights that you are going to plug into it.

For good results you must have a timer to control your lights.  Erratic lighting or 24 hour day lengths will be bad for many plants.  Be sure that you use a timer which is rated high enough for the total wattage of lights that you will be using.   Set the on period to correspond with or extend the  actual  daylight hours – in other words don’t try to have your plants day and night be opposite of the real day and night otherwise ambient light will interrupt their sleep just like it would yours.  I set mine to go on at sunrise and off at about 8 PM.  I currently have the day length set for about 13 1/2 hours, but when I start planting tomatoes and peppers in a few weeks I will increase that to about 16 hours of light per day.

Once I start this process every winter I love to get out in the plant room to visit and check on my plants.  The warm moist air and the smell of clean soil and growing things along with the sun light coming through the windows really takes the edge off of winter for me.  That and a cup of coffee is a great way to start the day.   Round up some seeds and soil, and see if it doesn’t lift your spirits as well.

My plant room

My humble plant work room.  Really just a small well insulated room on the side of my garage with 4 windows, and a concrete floor that I don’t have to worry about getting dirty.  The light bench is sitting on top of 5 steel barrels full of water for thermal mass which help to moderate the temperature.  You can see the rope light that powers my bottom heat there at the lower right.  On the far end of the bench I have just enough counter space to pot things up.  I love it.



  1. Cristina says:

    Good information. I found some helpful advice.
    I’ve bookmarked it for later!

  2. You really make it seem really easy along with your presentation but I in finding
    this matter to be actually something which I think I’d
    by no means understand. It kind of feels too complicated and extremely large for me.
    I am looking ahead to your subsequent put up, I will try to get the hold of it!

  3. It’ll also stimulate your flowers into rising a more healthy stalk.
    In a humid setting, the water can’t vanish as fast. You can start vegetables in a number of ways.

  4. I drop a leave a response when I especially enjoy a article on a website or I have
    something to add to the discussion. Usually it
    is triggered by the fire displayed in the post I read.
    And on this post Starting Seeds Indoors Under Lights ? The Door Garden. I was actually
    excited enough to leave a thought ;-) I actually do have 2
    questions for you if it’s okay. Is it only me or do some of the responses appear like they are left by brain dead visitors?
    :-P And, if you are posting at other places, I would like
    to follow you. Could you make a list every one of your communal pages like
    your Facebook page, twitter feed, or linkedin profile?

  5. Door Hi says:

    Hi I am starting the hydroponic plant, I am looking for the indoor plant as you do. This you share is good study for me. Please update the growing. I have question. How many electric cost in your indoor plant? I want to know to consider my plant. Thanks.

  6. cindy says:

    Thanks David, for the advice on leaving the heat mats on. I started doing so last night. The temperature chart really makes sense, if you think about it. I originally thought that the seeds/seedlings needed “down time” from the heat as well as the lights.

  7. Mireya says:

    Good information. Lucky me I ran across your website by chance (stumbleupon).
    I’ve bookmarked it for later!

  8. christi says:

    How many times do you transplant seedlings before transplanting outside? Mine are getting tall and spindly.Should I keep transplanting and going deeper? Someone told me I shouldn’t water much. What am I doing wrong?

    • David LaFerney says:

      I prefer to only transplant them once – into the ground.

      If your plants are tall and spindly they probably aren’t getting enough light. If you are using fluorescent lights like in this article the lights need to be very close to the tops of the plants because the intensity falls off sharply with distance.

      Unless your weather is still getting below freezing at night you should probably just plant them out – maybe with some cover like a milk jug with the bottom cut out. Try to plant them in the afternoon on a cloudy day so that the sun doesn’t scald them right off the bat.

      I water pretty much every day unless the soil is quite wet – as long as they are in containers.

  9. Allison says:

    Are you ever worried that resting the lightbulbs directly on wood is a fire hazard? I want to do this too, but it worries me..

    • David LaFerney says:

      No, but I’m not a worrier. Seriously, florescent bulbs barely even get warm – you can handle them with your bare hands when they are on with no discomfort at all.

      But if it bothers you you can certainly hang them from the ceiling or something. Don’t let that stop you from doing it.

  10. woould like to star a seedling bussiness please give guidance

  11. Hans Gruetzenbach says:

    You are totally correct. There is a reduction in germination as seeds age. There are several good sources on the Web giving reduction of seed germination over the passing of time.
    I personally discard any seed that are 2-3 years old. Their % of germination is just too low. This is why the Dept. of Ag. requires all seed be pulled off the shelves after one year.

    • Kirsten says:

      Hi Hans,
      Unfortunately, I’m a hoarder when it comes to my seeds :-) I typically have small gardens where my seed collections don’t end up getting used up for a couple of seasons and I’ve developed a few strategies to deal with it: I’m willing to pass seed on to friends and neighbors and, in return, ask only that they tell me in detail whether they liked growing the plant; and, as the years go by, I plant thicker and thicker to make up for poor germination. I try to store my seed properly, too, to lengthen the time it remains viable.

  12. Kirsten says:

    I’ve become a convert to supplemental lighting for starting plants. I still read about people who are able to grow seedlings using only their windowsill but that’s always been a disaster for me. Next up might be the bottom heat. I never used to need it but since moving to a rental house, I can’t find enough warm spaces to start the seed and I’ve had poor germination from my lemon basil and peppers because of it (I think – it could also be because the seed is old).

  13. Clayton says:

    Nice to find your blog. Some very helpful stuff for the home gardener. A little warmer climate than we have here but the principals are the same.

  14. Naseer says:

    Ok, we’ve had our heat and light setup going for about 10 days, and we’re seeing some interesting, and somewhat puzzling, results.

    We’re using the standard 72-cell Jiffy starter trays (9 cells x 8), and for some reason the perimeter plants all germinated quite well, but the interior plants had a much lower germination rate. In fact, for some plants (e.g. Juliet tomatoes), we saw 100% germination without bottom warming heat (though a few days longer) but only 50% germination with the bottom warming heat.

    This might be due to the water dripping off the lid only onto the perimeter cells, which would cause the center cells to be drier. Also, we thought maybe because the shop lights are directly over the middle of the trays that that is also causing extra dryness. Have you ever seen this problem?

    One other phenomenon we noticed is that once we took the tall seedlings out from under the cover, they constantly dried out. I guess it makes sense since they’re under heat and light, but we were surprised that even after 2 mistings a day, they would tend to dry out. Is that normal?

    On the plus side, we’ve seen excellent germination rate in the pepper plants with bottom warming heat, and near zero germination rate without the heat. Of course, it’s only been 10 days so I still expect the others to come up, given time.

    • You definitely need to maintain even moisture. The measures needed to do that will depend upon the temperature and humidity level of the room they are in. Make sure that the soil is evenly moist all the way to the bottom of the containers, and try to keep it that way. You might need more water than you can easily add by misting.

      You’re on the right track – You’ll figure it out.

  15. Naseer says:

    David, you’ve inspired us! My wife and I just started a gardening blog to talk about our gardening experiences up here in the Hudson Valley of NY. It’s only our 2nd year gardening, and we’re eager to learn as much as we can. Your blog has been incredibly helpful, and has already gotten a mention in the 1st and 2nd posts, where we documented the bottom heat and indoor lighting projects:

    Thanks for your detailed write-ups and your continued ingenuity in gardening on the cheap. Keep up the great work!

  16. Hans Gruetzenbach says:

    Hi Dave,
    My name is Hans. I live in Dalton, Ga.
    I love your blog and your ideas.
    I have been in gardening for 30+ years. The more I learn the less I know. Every new fact opens new avenues of knowledge.
    I have many years of experience in the horticulture business and always want and willing to learn more.
    I just recently gave a Free Clinic here in Dalton at Lowe’s, where I work part time, on starting seeds indoors and how to propagate plants from hard wood cuttings. I am in the process of planning another class on planting and growing bramblies, blue berries, and asparagus.
    Your idea on using flouesent lights in doors is great. It supplies adiquit light with out burning the plants. Everyone might want to know to use different type of tubes:
    Bright white, which produce a blue sprectum and Day light which produce a red spectrum, both of which the plants need to grow short, cobby, and healthy, taking the place of expensive grow lights.
    I never tell people what to do, I just advise.

    Hans P. Gruetzenbach

    • David LaFerney says:

      I completely agree, more specialized lights will certainly work better – I didn’t really know that combining those two bulbs was especially good for this application. Thanks for that useful advice.

      I try to demonstrate that you usually don’t *have* to use specialized equipment to get good results. If you want to start some seeds and you have a couple of shop lights, and you don’t have much money – Just use them, and it will work. When you are finished you can even hang them back up in the shop!

    • Gary says:

      I Also agree with your advice for 2 different bulb use . Used 1 coolwhite and 1 daylight in basic shop lights last season with great results. Glad to hear that someone else also good results and not just a fluke on my part using 2 different bulbs to broaden spectrum. Thanks hans. thanks dave as well . Love to hear other ideas and am definitely getting hooked on growing from seed.

    • NaseerNaseer says:

      Some good analysis of the different types of shop light bulbs here: (search down to “Industrial Tubes” if you don’t have patience for the entire article.

      I’m currently running with a mix of Sylvania Cool White ($15 for 10 at Lowes) and Sylvania Sunstick ($30 for 10 at Lowes). So far, we’re seeing fantastic results but I don’t know how much of that has to do with the bulbs vs just the fact that we’ve implemented a lighting solution (probably the latter).

  17. Chris says:

    Thanks David, for the advice on leaving the heat mats on. I started doing so last night. The temperature chart really makes sense, if you think about it. I originally thought that the seeds/seedlings needed “down time” from the heat as well as the lights. But, as you say, the little trays don’t have much mass and the temp drops from 75 – 85 degrees F to 59 – 60 degrees F at night. That’s a lot. So, we’ll see how it goes. Wow, this year has been a learning experience for me. I appreciate your blog.

    Happy gardening,

  18. Gary says:

    Just some suggestions I thought might be of help to others considering starting from seed.
    To keep plants and soil warm another good place to start is in a furnace room in basement if you have one. I tried starting from seed first time last year and this worked great. I just kept the domed trays covered with foil as well to hold extra heat and moisture in on an old ironing board close to furnace ( not too close)and had excellent results.
    Then I Moved them under the lights on my homemade 3 teir shelf made from left over 2×4 ‘s and plywood (Also kept in furnace room/side of basement) and placing some aluminum foil draped over the lights created a tunnel with alot of extra reflective light and gentle heat from the lights themselves keeping plants nice and warm once sprouting had occurred.
    Lastly,I used a small clip on fan blowing air through the tunnel created by the foil to create some air flow. This especially helped my second set of tomato plants grow stockier as it mimicked mother nature more and forced them to make a stronger sturdier stalk before it could grow up ward and ( leggy like first batch). Think other plants also responded well to this extra air flow.

  19. Kermit says:

    What problems are associated with having the lights on for 24 hours a day?


    • David LaFerney says:

      Flowering plants may start to form flowers at an extremely early age for one thing – which can stunt overall growth and as you would expect most organisms don’t successfully bear fruit until they are mature. Plants have circadian rhythms just like animals do, and they need a dark period or they don’t know what to do next.

  20. Joy says:

    David, have you ever used soil blocks. This is quite common in the UK but not here in the states? I find this so much easier when transplanting.

    • David LaFerney says:

      I’ve used peat pellets, and peat pots. I’ve never used the soil blocks that you press yourself. They sell all of that here – I guess I use to the plastic trays just because I always have. Not really a good answer, but there it is. Which exactly do You use?

  21. Chris says:

    Hi David,
    I have a quick question on seed starting. I also start my seeds under lights and I am using heat mats for the first time this season. I’m growing them indoors in my garage. I live in a place with a very moderate climate in Southern California. In your post you mentioned that we should “try to keep the soil as warm as possible 24 hours a day”. I’ve been turning my heat mats off when my lights go out (lights are on for 12 – 14 hours during the day). I have been wondering if I should be leaving the heat mats on. I read your blog awhile back where you described how you are using low wattage led string lights. I don’t recall how much heat they give off. But you gave the impression that it was equivalent to heat mats. I’ve been monitoring my soil temp (w/lights on) and it is usually between 76 and 81 degrees F. So, should I be leaving the heat mats on over night when the lights are off? My germination rate, currently is pretty good, but, I had several batches that were especially slow to germinate with some never germinating. They were mainly peppers and various varieties of tomatos.

    I’m also using similar “Ferry Morse” seed trays as yours. Another thing I wondered is if I should leave the plastic dome on when using both heat mats and lights. I saw the temp go up to almost 85 degrees F and I thought that might be too hot. Do you leave your dome on? If so, for how long; until the seeds germinate?

    Your advice is greatly appreciated.


    • David LaFerney says:

      I leave the bottom heat on 24 hrs a day because if you don’t the small amount of soil in your starting tray will cool all the way down to the ambient air temp over night. Unless that is pretty warm it is going to negatively impact your efforts. Out in the garden the ground has so much thermal mass that it will only cool by a few degrees over night, while in my plant room it might cool as much as 30 degrees. You might notice that volunteer tomatoes only come up in the garden after the weather is warm day and night.

      I leave the domes on unless I accidentally get it too wet in there in which case I take it off until it dries out. Once tomatoes come up it is probably best to remove the dome right away to keep them from getting leggy.

      Look at the temps in the chart found here – and you will see that for tomatoes especially 85 is not too warm. I’ve worried about that too, but so far too warm hasn’t seemed to be a problem.

  22. Shannon says:

    What a great little room. I started some broccoli seeds this weekend, but unfortunately don’t have such a nice space. I’m using a seedling mat with the little plastic pots under a ziploc bag. When they emerge I’ll put them under the aerogarden lights and start something different. It’s a very small scale operation but it worked for me last year so it should do all right. I like your set up with the shop lights. I might try to find a couple of those and duplicate that…Thanks!

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