It's easy to grow tomatoes from seed indoors under fluorescent lights. Not only is it easy and inexpensive, but it produces vigorous healthy plants. I have successfully grown a dozen different tomato varieties under ordinary cool-white fluorescent shop lights in an otherwise dark basement room.
Before we discuss more about the fluorescent lights, let's cover the basics of starting tomato seeds.
Bed Trays
Sterile Soil
Don't take a chance of introducing soil-borne diseases by starting seeds in regular garden soil. Instead, buy or make a soil-less mix like Jiffy-Mix, which is made from ingredients like peat moss and perlite. If you want to make your own mix just add equal parts vermiculite or perlite with fine peat moss.
Peat pellets and soil blocks
An alternative to a soil-less mix is to start your seeds in pre-formed peat pellets. These are slightly more costly but really convenient. Soak them in water and the peat pellets expand into small soil containers that can later be planted directly into a pot or garden.
Seed Trays/Flats
Any container can be used as long as it has drain holes. I buy the 72-cell lightweight seed-starting flats but they aren't required. You can also use the bottoms of waxed milk cartons, paper cups, open seed trays or individual containers. Any container should be about two to three inches deep. Seed trays usually include a clear plastic cover for the purpose of keeping the soil from drying out; this might be a concern if your indoor air is very dry.
Labels
Be careful when handling the small tomato seeds not to mix up the varieties because part of the fun is finding out which tomatoes grow the best. Then don't forget to label your containers. Write the variety and the planting date on the label. Plastic food containers like milk jugs make nice durable three-inch labels when cut up with scissors. Using an Industrial Sharpie pen will ensure the writing doesn't fade in the sun.
10 Steps to Planting Tomato Seeds
Fill the container with soil-less mix to within one-half inch of the top. Water the soil-less mix in the container and allow to drain. Tamp down the soil lightly with your hand. Place two or three seeds in each container (we'll thin later to one plant). Carefully sprinkle one-quarter inch of soil-less mix evenly on the surface. Tamp down the soil carefully to ensure good contact between seed and soil. Using lukewarm water, spray or gently water the soil surface until thoroughly wetted. Cover the containers with the plastic lid or plastic wrap to preserve moisture. Place the seed container in a location where the temperature is 75 to 85 degrees F (24 to 29 C) for fastest germination. After one-fourth of the seeds germinate, remove from heat source (if used) and move under fluorescent lights.
Fluorescent Lights
As soon as the tomato seeds have germinated, adequate light becomes essential. Ideally you'll provide 12 hours of sunlight per day to keep your seedlings from getting leggy and stretching for more light. If you have a sunny window or greenhouse with natural light, great! If not, you can spend a little or a lot on grow lights. I've found that simple 48-inch shop lights fitted with standard cool white bulbs work very well. You should suspend the lights two or three inches above the tops of the plants; hang the lights by a chain on a hook so that the height can be adjusted easily. You can build a cheap grow light stand (I have plans on my website) or you can use an old bookshelf with open sides. The thing is, you don't have to spend a lot of money. Don't worry if the leaves occasionally touch the bulbs because the lights don't get hot.
Sixteen to eighteen hours of fluorescent lighting per day works well. If you put the lights on a timer you won't even have to worry about turning them on and off each day.
Thinning the Seedlings
After two weeks or so the first true tomato leaves will have formed. At this point, the seedlings should be thinned to one plant per cell. I find it easiest to pull out the weakling with my fingers; another method is to snip off the extra plants with scissors at soil level. The goal is to not crowd the plants and end up with the strongest, sturdiest specimens. If you want to save some of the extras, then go ahead and transplant to their own containers.
Hardening the Seedlings
Brush the tops of the seedlings lightly with your hand each day or set a gentle fan to move the seedlings around. This hardens the stems and causes your tomato plants to grow stockier. This step reduces leggy seedlings and results in more compact plants.
Fertilizing
If you've used a pre-fertilized seed starting mix, you won't need need to fertilize. However, if some of the leaves are yellowing or no fertilizer was present, you can apply a liquid tomato fertilizer at half strength. Miracle Grow makes a tomato fertilizer low in nitrogen but high in potash and phosphorous that gives good results.
Transplanting Seedlings to Four-inch Pots
After the young tomato plants are four inches tall, they're ready to be transplanted to small pots. Fill the pots with seed starting mix or good quality potting soil and push aside a space in the pot to accept the root ball and stem up to the first leaves. Carefully remove the seedlings from the starting container with a spoon or dull knife being careful not to damage the stem. Plant the tomato seedling in its new pot, holding by its leaves or root ball, then add a little more soil and firm gently. Water well. Then, after allowing the plant a couple of hours to adjust, set the pot back under the lights. For the next several weeks, fertilize (following manufacturer's directions), and water until the plants are eight to twelve inches high and seven to eight weeks old.
Moving outdoors
You'll find that fluorescent lights work great for starting tomato plants. Now it's time to move outside and get some sun! Wait until the average frost free date has passed, and the soil temperature has reached at least 50 degrees F (10 C). Then "harden off" or condition the young tomato plants by placing them outside in a protected spot like a cold frame or a sheltered spot for a few hours each day for a week. This process will reduce the transition shock and firm up the plant for surviving all weather conditions. Then look forward to those luscious tomatoes!