tips for growing better tomatoes from seed

Cellpack of young tomato seedlings ready for transplant.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.

The tips:

  • 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.
  • 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.
March 4, 2009


  1. Jeannette says

    Hello, I planted my tomatoes 2 weeks ago, I live in Ontario,Canada and they are a little lanky. I have them in an indoor greenhouse, southern exposure,(no extra light) and no fan…I am guessing that is the cause after reading the posts. Also I was wondering if I should take off the clear cover before or after the true leaves?

    • says

      Hi, Jeanette. A little too early, I think. Here in USDA Zone 5B, where final frost is late May most years,the rule of thumb is to sow tomatoes the day our taxes are due (April 15) — meaning they will be 6 weeks old when we set them outside 6 weeks later, around the last weekend in May. The natural light is still a little weak and yes, I think a fan will help. Do you have more seeds to start next month?

  2. says

    Until this year, I bought a ready-made tomato seedlings. Now I want to try to grow their seeds. Your recommendations in this regard are very valuable and timely. Thank you.

  3. says

    When Jenny and I first started gardening we bought our plants but the last few years I have been growing our garden from seed. It’s so much more fun starting them early, in the house, and seeing them come from seeds.

    Last year was our best year for tomatoes even though I tripped with on of my tomato trays and lost a bunch of them before they had a chance to really get started. So we did very little canning. This year I will walk more carefully with the trays.

    I have a couple of fans that don’t work well. I am going to use them to toughen my seedlings. Thanks.

    • says

      Ouch, James…sounds like quite the stumble. :( I carry my seedlings in and out on fair days and keep thinking “go slow, Margaret; easy does it,” since the trays are wobbly, you know? See you soon again I hope.

  4. says

    I have a VERY unorthodox method for germinating tomato seedlings…my three rescued pot belly pet pigs do it! Here’s how — about 4 weeks before I want seedlings for the garden I mix packets of organic heirloom tomato seeds in with the pigs’ food. They poop out the seeds in little ready-made fertilizer poop pellets, and I rake and dump the poop into one of several compost piles I have around the farm. I water these piles and within a few days the top of the pile is COVERED with tomato seedlings. I put on rubber gloves and transplant these very hearty seedlings to raised beds in my garden. Some I leave growing on the edges of the compost piles…some I transplant to the pigs’ outdoor play area so they can enjoy fresh-from-the-vine tomatoes in a few months…and the process begins again. I have gifted these special seedlings to gardening friends who claim these seedlings are amazingly strong and resilient. Sure they are – they have been through the insides of pigs! People think I am joking about this method, but I am quite serious. It grows the most amazing tomatoes. Of course, you need a pet pig…but there are pigs who need rescuing from city folk who think they stay small and cute. There is no such thing as a Micro-Pig or Teacup-Pig or Pocket-Pig!

  5. Mark says

    I live in the south of Thailand so we don’t have frost. Our temperatures are 17c (62f) to 30c (86F) all year round. Temp for today (middle of winter) is 25 – 32 celcius.
    I threw the seeds into an old flower tray outside and they have started growing! . I’m also growing marigolds as I heard they keep pests off. There is a gentle breeze most of the day so I’m hoping that will make them sturdy. Tomatoes are not traditionally grown this far south and I m hoping I don’t find out why. They were in a shaded spot and as I’ve just read your website saying they should get full sun I’ve decided to try them in that for a couple of hours a day. I actually think full sun will be too strong for them so will limit it. Will post results if I get any!

    • LaRieta says

      Good luck!
      I have tried to grow tomato plants many times while in Dallas , Tx. That Texas sun is hot.!! I am learning. smiles. I started seeds inside.., very early, then put them outside early spring HOWEVER I had to watch weather in case of too cold nights..There were many . lol I covered them and I did have lovely plants and much fruit.

  6. David Thorne says

    Thanks for this website & info on growing tomatoes from seed. I have always had the problem with skinny spindly plants before setting in garden but they eventually make it.

    My question is: How warm should it be for the seedlings after germinating and they are moved to a well lit area. We keep our house at 62 F daytime and 56 to 57 F nightime.

    We live in zone 5A

    Many thanks and again thanks for this website, I will be doing more exploring.


  7. Cathy says

    Thank you very much for your insight and expertise. I have tried year after year to grow from seed. Many times I end up with mold growing on soil/potting mix. Or letting them dry out. I currently have several herloom tomatoes growing and they are quite past the stage where I have killed them in the past. My husband made me some wonderful cold frames. I may set them out here and there on nice days. After this long winter I can’t wait to get dirty in the garden. ;D

  8. Mary Veldman says

    I started my tomatoes by seed April 2. I decided to go with moon cycles. My grandmother always said to start growing at the beginning of a new moon cycle.

    10 days later I have 70% germination. Plants are 1 1/2 inches tall with first set of leaves. I used peat pots.

    My question is, do I replant them now into 4″ pots ? Or do I wait till they have their second leaves?
    I live in Beausejour Manitoba Canada, 2B climate. I should have have waited till the end of April to plant seeds but needed to think green .. I will start more tomatoes by seed on the 15th, and 30th for comparison sake.
    I have no greenhouse, only windows for sunshine and plenty of time on my hands.

    • margaret says

      Hi, Mary. I like to wait till they have 2 sets of “true” (tomato-like) leaves, since they are a little sturdier, but most of all I like to not have to pot them on. :) (I start in big-enough cells to last 6 weeks in place, and use nail scissors to cut out the “extra” seedling in each cell.)

  9. Virginia Jackson says

    Hi I started my tomato seeds in those peat pellets and have transplanted them into the jiffy pots with bought soil.The leaves from the bottom keep turning yellow and these r not the first leaves.To much water or not enough?Wondering if it has to do with them started in those pellets.I live in Stony Mtn. Manitoba Canada and never had this problem b 4. Any suggestions? They r in front of a large window.

    • margaret says

      Hi, Virginia. They need to stay warm, have LOTS of light (much more than a windowsill can offer), and once they germinate you don’t want to keep them as moist as before germination. (Seeds need more moisture to germinate than the young plants want once they emerge.) I haven’t used pellets in eons, so I don’t recall how hard they are to manage. Here’s how much light you need.

  10. Marion says

    Hi Margaret, Question for you … My tomato seedlings are doing very well in APS12 cells. They have one set of true leaves. When they get the second set of leaves, do I need to transplant into a larger pot or will they be OK in the APS12 cell?

    • margaret says

      Hi, Marion. I keep them in those cells up to about 6 weeks typically…then put them outdoors in the garden…to avoid potting on, but some varieties grow more lustily than others, and so may want an upgrade. So it’s a matter of how long till transplant date and which varieties and so on — meaning you have to eyeball it. You don’t want them to suffer if they are outgrowing their cells, but I usually go for a 4-inch or 5-inch plant timed to go outside at 6 weeks of age.

  11. Michele says

    Hello, my tomatoes were started indoors. I planted in about two weeks ago in 5 gallon pots. They have full sun from around 6:30 AM to 1 PM. But they are only about a foot high. I’m wondering if growing in a pot, and this pot is conical shaped like traditional flowerpots are, the dirt becomes so dense that the roots can’t move. It just seems like tomatoes grown in looser soil grow faster.


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