tips for growing better tomatoes from seed
THAT OLD, DISCARDED ELECTRIC FAN that isn’t strong enough for the hot summers of global warming…hey, bring it on. It’s perfect for accomplishing one of the tricks to growing better tomato seedlings, which is (after all) the only thing you probably really care about right now. To hell with winter. Onward!
It’s still too early for sowing tomatoes here, with April 15 my target date, but I can dream. Those of you in warmer zones can stop dreaming, and do (and if you already sowed, it’s not too late to start petting your plants to help them grow sturdier…really). The goal is not a tall seedling by transplant time but a stout and sturdy one, about 4 inches high and wide.
- Work from your final frost date to determine when to sow (calculate it here; mine’s early June).
- Count back from 5 or 6 to as much as 8 weeks. Everyone has their own beliefs on this. I like a strong little plant grown in a medium-large cell, so 6 is plenty; my seedlings would need larger quarters (like a 3- or 4-inch pot each) to thrive for 8 weeks indoors; more work, but to my mind no extra benefit.
- Seeds germinated on a heat mat in flats will get off to a particularly fast start. A soil temperature of 70 degrees is essential; higher (like mid-80s) is better in those early days. I did not use a heat mat until recently because I sowed directly in APS cells (insulated, self-watering foam trays that last many years), not seed flats; lately I’ve been doing some of both.
- If you’re re-using seedling flats or APS or Speedlings (another polystyrene system) or other containers, first clean everything with a 1:10 bleach:water solution.
- Start with fresh seed-starting mix. A soilless mix (they are usually peat-based) is best. This is not any old potting soil; it’s specially formulated for seedlings.
- My hero, James Underwood Crockett of the original “Victory Garden” series, would sprinkle 6-8 seeds per 3-inch seedling pot, then after about two weeks, or when the plants were 1½ inches high, transplant them into 6-packs, one plant per cell. Confession: Rather than transplant, I usually put two seeds per cell and use a nail scissors to cut out the weakling, skipping the potting up. I start with slightly larger cells than a conventional plastic 6-pack, however; others swear by transplanting each baby to its own 3- or even 4-inch pot.
- Barely cover seeds after sowing with ¼ inch more mix and tamp down, then moisten thoroughly (easiest with a spray bottle). If you are using a bottom-watering system like APS, mist the tops, then fill the water wells.
- Keep the covered trays in a warm spot (no light needed or even desired); the heat mat will create all the warmth you need. Again, 70 degrees is the minimum requirement, and the desired temperature throughout their young lives.
- Do not let the seeds dry out before they germinate.
- Germination will take place from a few days (with early varieties) to 10 days or so. A consistently moist environment is essential, but don’t let them cook or drown, either; vent the lid or bag so no moisture beads are ever running down the sides.
- Once up, it’s critical to move the babies fast off the heat mat and into a high-light situation or they will stretch out and be useless. Forget low light. Even new T-5 grow bulbs (high-output fluorescents) in a reflective hood provide only a fraction of the light outdoors; read up on why seedlings stretch and get spindly. Set a timer for 12 hours minimum a day (some think 14 is better), and keep the lights very close to the plants (a couple of inches maximum, meaning some form of adjustable setup).
- Feed with half-strength water-soluble fertilizer after the first true leaves appear. IMPORTANT: If the seed-starting mix you bought includes fertilizer, go easy or skip this step. Overfertilized baby plants can stress out and even die. If using unfertilized mix, plan to feed at half-strength twice during the plants’ indoor growing period.
- They will grow fast now, and this is when you must transplant if you sowed in “community pots” or they’ll become overcrowded.
- Don’t water with cold water; and never douse. Mist, with tepid water, or use a device whose spout delivers gently. I’ve known people to use everything from a houseplant watering can with a very narrow spout to a discarded soda bottle with one of those pop-up tops. Some systems have wick-like mats beneath the cells that draw up moisture.
- Turn on the fan, on low, not right next to the plants but so they feel it a little bit. This helps strengthen them, like young trees whose trunks grow stronger in the wind. Air movement also helps prevent deadly fungal diseases like damping off.
- Brush the tops of the seedlings daily with your hand to provide the “mechanical conditioning” that creates sturdy, not spindly seedlings. Not just once, but gently for a half-minute or minute. (Yes, go ahead, talk to them while you do it. I probably do without even realizing it.)
- If the weather is somewhat settled, I carry my flats outdoors for at least a few hours a day, setting them in a sunny but protected spot. The light is just so much stronger.
- If any flower buds form on your young plants, pinch them off. Don’t let the baby stress itself trying to reproduce just yet.
- More, more more: All my Tomato-Growing FAQs are on this page, or read all my Tomato-Troubles FAQs (in case you encounter any pest or disease). My vegetable-seed calculator tool can tell you when to start your tomatoes and other crops.
- All sound like too much trouble? You can direct-sow tomato seed right in the garden if your season is 4 months or longer between frosts…and if you are vigilant about weeding, watering and all the other steps in tomato TLC. And of course you can also just buy seedlings, locally or by mail. I like to make sure I’m growing from regionally adapted seed for best results with my tomatoes (and many other crops). The reasoning on that, and why I think it’s worth it, if a great-tasting tomato is what you’re after.