The season is just getting started, and already reports are coming in from gardeners having trouble growing tomatoes from seed. Fortunately, there is plenty of time to start over, which may be a good idea. Tomato seedlings emerge fast and show vigorous growth under warm, bright conditions, so there is little point in starting seeds very early.
Tomatoes are the first veggie many gardeners grow from seed, mostly in pursuit of interesting varieties that are rarely available as seedlings. To improve your shot at success, here are my top tips for growing tomatoes from seed.
If you are reusing plastic cell packs, wash them well in warm, soapy water to remove old soil and accumulated salts. My favourite containers are small paper cups with several holes punched in the bottoms, because I can write the variety names on the cups. When the seedlings are ready to move to larger containers, it’s easy to peel away the softened cups and compost them.
Also use a new bag of high-quality seed-starting mix. Avoid cheap imitations, which are often the cause of seedling failure.
Write variety names on them with waterproof markers, or you can make labels from utility tape. Labels work better than little stakes, which wiggle around amongst the tomato roots and can be accidentally lost. I learned this one year when a gust wind toppled the table that held dozens of seedlings. Most survived with prompt repotting, but I had to guess which markers went with which tomatoes. Labels work better.
The furry coating on tomato seeds softens and gummifies when water is added, which helps the seeds stick in place among soil particles. The seed coats also release chemicals into the soil that enhance growing conditions for the soon-to-come roots.
I use a pump spray bottle to thoroughly moisten the seed starting mix, which can take several hours. When the containers feel heavy with water, I use a pencil eraser to make shallow holes for the seeds, and cover and press them in with my finger. Then I spritz more water over the top. If you are not sure about the purity of your water, use filtered water that has been allowed to gas off overnight in an open jar.
Tomato seeds kept at warm room temperature and sprayed with water twice daily should sprout within a week. As soon as the seedlings break the surface, move them to bright light. A full-spectrum grow-light is ideal, but a sunny window will do provided the seedlings are watched closely to make sure they don’t dry out.
I like the phrase “potting on” for moving a seedling to a slightly larger container, which happens twice with my tomatoes. Soon after the first true leaf appears, I move the seedlings to larger paper cups or small plastic pots. Most of them must be potted on again three weeks later.
Never touch the main stem of tomato seedlings, because the juicy tissues are easily bruised, and bruises serve as entry points for the fungi that cause seedlings to rot. The main stem also can be damaged if a seedling falls over, which sometimes happens when a weak-stemmed tomato seedling becomes top-heavy with new leaves. Prevent fall-overs by sprinkling additional seed starting mix around the base of leggy seedlings, and press it in. To further support seedlings until you can repot them, prop up leaners with toothpicks or a wood skewer.
Avoid the temptation to plant little tomato seedlings in large containers, which can cause the skimpy roots to become overwhelmed by soil microorganisms. It’s better to pot on seedlings to a slightly larger container as soon as you see roots growing through the bottoms of the containers.
Gradually expose your indoor-grown tomato seedlings to increased sun and wind. An opaque storage bin with the lid removed makes a good hardening-off chamber, or you can use a cold frame or protected plant shelf. Allow at least a week for your plants to prepare themselves for outdoor life.
With a little practice, you can expect great results growing tomatoes from seed. Tomato seedlings that enjoy stress-free lives with no serious setbacks quickly adapt to garden life, and few things are more rewarding that harvesting sun ripened tomatoes from plants you started as tiny seeds.
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