If you’re like me, you started your tomato seedlings too early and now they’re long, spindly vines falling over and getting tangled with one another. Last year, I started mine a few weeks earlier than I should have, and then our late spring kept them indoors for two weeks longer. I wish I had a greenhouse. Don’t we all wish that?
I grow about six hundred tomatoes each year. Although they don’t come out greenhouse-perfect, I do manage to keep the seedlings healthy, robust and reasonably compact. It’s just a matter of maximizing their light, potting them as deeply as possible, and pruning without mercy.
Maximizing the light
In late winter, the strength of our sunlight is only about one-fifth of that in midsummer. It looks pretty bright on a snowy day, but the intensity of the sun is less than you might think, and the day is significantly shorter. Even on the best windowsill, seedlings do not get enough light to grow normally. They inevitably grow long, slender stems, reaching for more light, until they bend and break or tangle with their neighbours.
Many household gardeners shy away from the cost or complexity of grow-lights, but it isn’t as hard or expensive as you might think to provide supplementary light for your seedlings. Depending on how many plants you have, you can set up a small low-power lamp on your windowsill to give extra light in the morning or evening. Or, you can construct a simple, low-cost light shelf in a basement or heated garage.
I grow plenty of seedlings in my basement with a three-shelf set-up that I made for about $80 with scrap wood and second-hand light fixtures. Two plywood shelves (48×22 inches) are mounted in an open box frame of 2x2s, six feet tall. The first shelf is two feet from the floor; the second is two feet above that. You could put a third shelf at the top, but it isn’t necessary; all you really need are a pair of 22 inch rails to join the tops of the verticals on each side. The experienced builder will know that it’s also a good idea to put a few diagonal cross-braces on the back of the unit.
Mount 48 inch fluorescent light fixtures under each shelf and from the 22 inch rails at the top of the unit. This provides light for four standard plastic garden trays on each shelf, and four more on the floor. I strongly recommend two fluorescent fixtures per shelf (that’s four tubes per shelf). Suspend the fixtures on lightweight chain from small hooks screwed into the wood, so you can easily raise and lower them. In my set-up, I connected the fixtures so that each shelf has its own switch, and that saves a lot of electricity when I only need one shelf at a time.
Whether you build a light stand, or just plug in a lamp, remember these two tips: make use of reflected light, and don’t be afraid to use cheap fluorescent lights instead of expensive grow-lights. You can easily capture light and reflect it back to your seedlings using aluminium foil or white surfaces. My light shelves are painted white for this purpose, and the back and sides of the unit are covered by cardboard panels lined with aluminium foil. Very efficient. It’s also efficient and safe, to use standard, inexpensive “cool white” fluorescent tubes. These are “cool” both in temperature and in colour. Even after several hours, they only become comfortably warm to the touch so you shouldn’t worry about your plants (or your house) burning. Moreover, they mostly emit light in the blue spectrum, unlike expensive grow-lights which emit full-spectrum light. Mature plants need full-spectrum light to produce flowers and fruit, so grow-lights are helpful in greenhouses where extra light is necessary to stimulate flowering. Young seedlings, on the other hand, respond very well to blue light. So save your money, and only use full-spectrum grow-lights if you want to produce flowers indoors.
Tomato seedlings have the remarkable property that they grow roots from their stems wherever they contact soil. You can bury the stems right up to the leaves, and they will happily just grow more roots. To help keep my tomato seedlings compact, I repot them once or twice while they’re indoors. At the two-leaf stage, I dig them out and carefully replant them at the very bottom of a small container. By filling the container, burying the stem so that only the leaves stick up above the soil, the seedling is shortened and it becomes stouter and stronger. If you have room for larger containers, you can keep re-burying seedlings to shorten them until planting time arrives.
When you plant in the garden, you have one more chance to shorten the seedlings. Even if your tomatoes are very long and stringy, plant them so that only the top four or five leaves are above the soil. This helps prevent the stems from blowing and breaking in the wind, and it adds to the root mass. The seedlings will grow very quickly once they take hold, and the lost height will be made up before you know it.
Pruning without mercy
The easiest way to shorten tomato seedlings is also the most difficult for beginners. You have to do this a few times before you can really have faith that the little plants will grow back. Believe me, you can prune your beloved seedlings quite hard, and they will thankfully grow back healthier and stronger.
My favourite method of pruning tomato seedlings is to pinch the tops when they have three good, strong leaves and a fourth emerging—about 3–4 weeks old. Tomato seedlings have alternate leaves—one leaf grows out one side of the stem, then another grows out the other side a little further up, and so on. The original seed leaves fall off soon after the true leaves start to grow: don’t count these. When you see the fourth leaf beginning to unfurl on a little stem, snip or pinch it off above the third leaf. What happens?
Nothing seems to happen for about a week, which is good because the plant is growing a stronger stem and roots instead of more leaves. Then you should see more strong growth at the top and sides, which you can pinch or train as you wish. This happens anyway later in the plant’s life (many people call the side growth suckers) and there are many theories and religions based on suckering (whether or not to, and how and when to do it). I won’t get into that right now.
By the time you plant your seedlings, they will be stockier, fuller and healthier than the long, stringy tomatoes that they might have been.
Good care and good weather are still the most important ingredients for a good harvest, but early in the year we have more control over our plants and it feels good to put healthy seedlings in the newly-prepared garden. I hope your spring is full of promise, and your harvest is full of delicious lovely tomatoes.