Should I just buy a 48" shop light? I have two 10 x 20 flats. I've never done seeds indoors. I have about 6 weeks until our last frost date, May 15 in Chicago. I already started the seeds on a heat mat with domes. I didn't realize they sprouted already. Now I am in a panic. The grow light I bought seems to be too small. 18W Grow Light. I'd like to buy something today at a local big store.

  • Why do you think your grow light is too smalll? Are the seedlings becoming etoliated? Are you supplementing them with daylight from a south facing window? Commented Mar 31, 2018 at 22:33
  • I'm probably going to start new seedlings today. They are etoliated. I had to look that word up. They're in a south facing patio window and I just started the grow light today after taking off the dome. I'll take them off the heat mat later today. The light is teeny. Each lamp is about 1/2 inch wide by 10 inches long. Commented Mar 31, 2018 at 22:45
  • Don't worry about the seedlings being etiolated - you can repot them deeper and the tomatoes will set roots from the stems. In fact, you should repot them several times before setting them out.
    – Jurp
    Commented Apr 1, 2018 at 0:38
  • I am posting a link to amazon for a light I bought, might be something worth looking at, I just bought 4 of them and they have been doing just fine for me. amazon.com/gp/product/B06VTV6QMY
    – Ljk2000
    Commented Apr 1, 2018 at 3:11
  • LJK That light looks interesting. How many inches, or whatever measurement. of seedlings are you using those lights for? How long have you been using them? Are you using them on their side like on the picture or over the top of the plants? Commented Apr 1, 2018 at 4:22

4 Answers 4


This site says you need 50 Watts per square foot of grow area. So, just calculate your required Wattage, and then purchase a grow bulb of the required size.


I grow my tomatoes under two 48" shop lights, with no special bulbs (they need the extra light the wider spread of two lights provide). I hang the lights from my basement ceiling with chains, which I raise as the tomatoes grow. As noted in my comments, I repot the seedlings into deeper pots as they grow - generally from normal seed-starting cells into 4" pots, then 1 quart (a deeper 4" pot) and maybe a gallon pot, each time, burying them deeper.

I don't usually start my seedlings until the second week or so of April, though (in Wisconsin) - you're a bit early :)

If the plants are etiolated when May 15th comes, just bury them deeper in your garden. Some experts say to not remove any leaves, but I've found that you may have to if the plants are too leggy.

  • Jurp, that is really helpful. I bought one shop light with two T8 bulbs. When do you put them in the 4" pots? I have some 3" pots. I figured maybe after 2 or 3 sets of true leaves? Tomato plants don't seem to have that big of a root system. Why do you need to keep transplanting? I am wondering if it's to keep burying them deeper so they get more roots around the stem? Commented Apr 1, 2018 at 4:31
  • They're 32W bulbs. I wonder if I should move them away from the window? Why do you wait until mid-April to start your seeds? I usually wait until June 1 to plant. But a couple of years ago I jumped the gun and planted them out early in May. It got down under 40 one night. I bought a bunch of straw bales and mulched them up to the top leaf set. It stayed cold out for weeks. But all the plants were the best tomatoes I've ever grown. Both in taste and quantity. Also disease resistance! Commented Apr 1, 2018 at 4:51
  • One light with two T8 bulbs will be fine when the plants are young, but the plants will probably get leggy as they get older - too many leaves for the amount of light given off by the bulbs. This is why I use two pair of lights (I also have the room for the lights). I put the seedlings into 4" pots when I can see roots popping out the bottom of the cell - usually when they're about 3" tall. All my other repotting is done to provide more room for roots - I plant a little deeper each time to account for some etiolation but mainly to get more roots off the buried stem -- like you guessed :)
    – Jurp
    Commented Apr 1, 2018 at 13:51
  • If you have this light next to a window, then you're getting supplemental light, which may mean you don't need the second set of lights - but watch for legginess. When I was growing up in Milwaukee in the '60s, the rule of thumb was to wait until Memorial Day (May 26th back then); Milwaukee has jumped nearly two full hardiness zones since then. Back in the late 1980s, I ran some tests: 2 plants in "Wall-O-Waters" in mid-April, two plants May 1s (no protection unless frost imminent), 2 plants May 15th, two May 30th. All same varieties, same garden.
    – Jurp
    Commented Apr 1, 2018 at 13:59
  • My tests found that best yield was from plants put out May 15th, which were slightly better than those planted May 30. I don't worry about temps unless they're near freezing, which hasn't happened around here in maybe 10 years. Last three winters in southern Wisconsin were Zones 6a, 6a, and 5b. In the 1960s, this was a cold Zone 4.
    – Jurp
    Commented Apr 1, 2018 at 14:01

Your biggest problem will be soil too warm after sprouting , this will make seedling too tall/leggy. Long ago I grew many plants from seed in Chicago area. Once sprouted , I moved the flats to a garage that was usually 50 to 60 F. I used 48" shop lights with a mix of grolux and white bulbs but I added 2 incandescent sockets to each hood with 60 watt bulbs ( there were no LED or fluorescent bulbs then ). I put the lights very close to the plants, occasionally leaves burned on the incandescents but that did not slow the growth. Today , I would use LED lights and would not need incandescents . Put the lights very close to the plants. When it was probably not going to freeze anymore, I just planted them outside : Except heat lovers like tomatoes, peppers and eggplants , I would keep then under lights until late May.


I ended up getting four 48" double bulb shop lights. I started with 10 flats on heat mats. Transplanted into 3 or 4 inch pots, then 6 inch, and hardened them off outside about a week before I planted them out. It didn't seem to mater which bulbs I used. I tried different kinds the next summer. It Worked great.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.