There were several questions asked on my last early tomato post so I thought I should expound on what has worked well for me. I have grown most of my vegetables and annuals from seed under lights for years. I have made many mistakes along the way and have developed a system that works well for me. There are a few simple tips that I have learned that might be helpful to you.
The five most often overlooked tips for growing successful seedlings:
1. Use a lot of light!
If you think your seedlings aren't getting enough light, you're right. And if you think they have enough light, they could still use more. With florescent light fixtures I am trying to mimic the bright and powerful sun, so the more the merrier. I like to have two fixtures per flat (four 40 watt bulbs). I don't use special light spectrum grow bulbs. They are an unnecessary expense. Although it is important to use new bulbs each year because the light bulbs lose some of their brightness as they age. I keep the lights on between 16 and 18 hours per day.
2. Keep the plants close to the lights!
I make sure the light fixtures are only an inch or so above the top of the plants. Remember, we are trying to give them the power of the sun, not the moon. Don't think in terms of how much light we need. I would rather err on the side of the plants touching the bulbs than too far away from them. Being too far from the bulbs causes tall spindly plants.
3. Use good growing medium!
I use the soil-less seed starting mix in the beginning and transplant up to a mixture of potting soil and peat moss. Do not use straight potting soil because it doesn't hold water well enough. You need the peat to keep the roots constantly watered.
4. Give them plenty to drink with bottom watering!
All of my containers have holes in the bottoms to allow water in (or out). Peat pots work the best for this. I put the cell packs, newspaper pots or peat pots in a plant tray that will hold water. Then I fill the tray up about half way and the porous soil medium wicks up the water to feed the roots. I water almost every day. I am convinced that this is where the most mistakes are made with growing seedlings. Constant light can dry out the soil quickly which stresses the plants. If you try to spray your plants from above, they probably don't get enough water. This is why I am struggling with using soil blocks. Since they aren't in a pot you can't bottom water them. I haven't used them for my early tomatoes. I will try again with the main season tomatoes.
Incidentally, making sure my plants are watered frequently enough is why I don't use automatic timers to turn the lights on and off. If I have to do it manually I am more able to monitor the soil moisture.
5. Get your timing right!
Make sure you know when you plan to move the plants outdoors and the growth habit of each kind of plant you are raising. Research the recommended seed-to-transplant time for each vegetable or flower. For instance, tomatoes should only be under lights for 4 to 6 weeks before transplanting and you shouldn't transplant them until all danger of frost has passed. In my area, the average last frost is May 15th. That means that I should wait to plant the seeds of my 27 main season tomato varieties until mid-April. If timed correctly, you do not need to pot-up very often. Of course for my extra-early tomatoes I transplant them two or three times and have them under lights for 8 to 10 weeks but that is unusual. For most of my flower and vegetable seeds, I try to wait as long as possible. Real-estate under grow-lights is at a premium, even for a big bench like mine. Be careful not to take up unnecessary space by planting too early.
Now, If you have never tried starting your own seeds indoors with florescent lights, I hope posts like these don't make it look too complicated. I love managing the plants under lights. For me it is great fun. It is especially rewarding because I know that I can truly raise organic vegetables. I get to control the plants' environment from start to finish. It is also fun to grow seedlings because you get a chance to get your hands dirty when it is still too cold to dig in the outdoor garden. I would recommend any gardener give seed-starting a try.