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 on the run-up to another spring. To hell with winter. Onward!

It’s still too early for sowing tomatoes in my Zone 5B Hudson Valley, New York, area, 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 a.k.a. brushing your plants to help them grow sturdier…really). My goal is not a tall seedling by transplant time but a stout and sturdy one, about 4 inches high and wide.

Homegrown heirloom tomatoes

the top tomato tips:

  • Work from your final frost date to determine when to sow (mine’s late May-early June). Use my seed-starting calculator to get your start date (and a link to figure out your frost date if you don’t know it).
  • 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 6ish 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 not much extra benefit. Again: many experts prefer 8 weeks, and you may, too.
  • 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 of germination. I did not use a heat mat until recently because I sowed not in seed flats but in insulated, self-watering foam trays called APS that last many years, but have sadly been discontinued; lately I’ve been doing some of both.
  • If you’re re-using seedling flats or other containers, first clean everything with a 1:10 bleach:water solution or at least hot, soapy water.
  • Start with fresh seed-starting mix. A soilless mix is best. They are usually peat-based, but with consciousness about non-sustainable peat lately, coir is often used. This is not any old potting soil; it’s specially formulated for seedlings.
  • My earliest 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.
  • Or try NC Tomato Man Craig LeHoullier’s “dense planting method,” and really pack the seeds into every cell. Amazing.
  • 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, 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 with heat-lovers like tomatoes.
  • 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 T5 grow bulbs (high-output fluorescents) in a reflective hood like this or this 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 recommend 14), and keep the lights very close to the plants (a couple of inches maximum, meaning some form of adjustable setup like hooks and chains, to adjust as they grow).
  • Feed with half-strength water-soluble organic 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. Discard the weakest or runt-like seedlings–or snip them out with a nail scissor to prevent disturbing roots of the desired plants.
  • Don’t water with cold water; and never douse. Mist, with tepid water (I use this device), 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 or even a cream pitcher. Some seedling 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 may also help 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 any flower buds form on your young plants, pinch them off. Don’t let the baby stress itself trying to reproduce just yet–not till they are settled in the ground.
  • 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). I think it’s worth it, if a great-tasting tomato is what you’re after. The best-tasting tomato is a combination of nature and nurture, you see.
  • One more thing: How-to’s on tomato staking, pruning, and disease management outdoors.

(Disclosure: Purchases from Amazon affiliate links yield a small commission.)

  1. Linda Jean says:

    Yes, I also use the APS system for most of my seed starting. It’s practically idiot proof. One can go away for a weekend knowing all is well. And I like the germinating and transplant mixes from Gardeners’ Supply. The only trick is to show restraint and not start too soon or one soon has dozens (and more dozens) of potted up babies when it is too early to move them to the unheated porch but there is not enough room under the lights. But the last week in March works well for me here in Central New York to start the annual rites of spring in the basement.

  2. leslie land says:

    great post! Especially with all the links to further details. And I love it that you got in the air circulation and mechanical conditioning; those steps make such a big difference.

  3. Alejandro says:

    I start mine about 8 to 10 weeks before my last frost date. What I do is I transplant them twice: I start them in plugs and from there they first go to a 4 inch pot, later to a deep and narrow pot, cutting the lowest pair of leaves and burying the plant up to the next pair of leaves each time I transplant it. What I end up having is a small and sturdy plant on top of a very tall tube full of roots. Much better than the plants you can buy @ nurseries that usually have a small bundle of roots and lots of leaves.

  4. Willi says:

    This post is so great! When I was in high school I worked at a small nursery and my job was to start the tomatoes. I started an entire greenhouse every spring. Those plants were my babies and in summer I liked to think about them growing in backyards all over town. My only two cents is when up-potting only handle the seedlings by their leaves. The stems are still really delicate at this point and it’s easy to squish them and kill the plant.

  5. chris says:

    this is a great piece on growing tomatoes from seed. since i split my time between city and country, i buy plants, typically from burpee. works out ok since if they don’t perk up after delivery and before planting, burpee replaces them no sweat. my only add to would be to continue to pick at flowers until your plant looks like it is really rearing to go. while you can’t do this indefinitely, as this would eliminate the tomatoes (duh), i do this longer than most, and i find i get very vigorous tomato plants indeed.

  6. Here (Netherlands) we usually don’t get frost after the ice saints have come and gone. Which is a fancy way of saying after half May. ;-) This month I will really get cracking with the sowing. I’ve done a bit last month but not much. I’ve found that sowing in March works best for me.

    BTW great tutorial on how to raise a tomato plant from seed.

    1. margaret says:

      Welcome, Yolanda. As with so many comments here, I just learned something new: about the ice saints. Thank you. I had heard of St. Pancras but didn’t know the bigger story. Here in my zone the ice saints can visit in May (or even early June), but after mid-May we get gutsy and set tender things outside, just keeping some old sheets and tarps around for emergency overnight duty.

      By the way, I have shown my Jack your menagerie and now I am in deep trouble: He, too, wants homepage promotion here with glossy color celebrity photos and reports on his every accomplishment and activity. I already had to make a place for my frogboys here (and now on their own frogblog, too) so I don’t know.

      When I relaunch A Way to Garden this weekend, with some enhancements (if I live that long), he will have a little more play…but enough is enough, you know? I continue to delude myself that this is my house, garden, blog. Isn’t it? (Please say yes, someone.)

  7. Eric : Gardenfork.tv says:

    Good points here. especially about using a fan, you don’t want it blasting the plants, but you do want some air flow.

    I’ve found my tomato plants get too big for the six pack APS trays, so i transfer them to quart yogurt containers, burying them deeper in the pot than they were growing in the APS trays. More roots will grow out along the stem that is now below the soil.

    The experts at White Flower Farm tell me that you can put tomato plants early than the conventional wisdom dictates. The plants may not show much top growth, but the roots are growing.

    I use home made grow lights, and I made this how-to video to show people how they can do it too. I’m one of the 16 hour a day advocates.


    1. margaret says:

      Welcome, Eric, and thank you for the video link. Good stuff.

      As for earlier planting, I am going to differ with WFF (having tried every method of gun-jumping here in Zone 5b for more than 20 years…wall o’waters cloches, Reemay, out in the open, you name it). I think they HATE the cold. And I HATE all that rigging-up of protective devices when NOAA weather says “frost warning” unexpectedly the night after I set out the babies. So I just wait. At least till Memorial Day (if not June 1ish). I don’t think I gain anything by rushing, and goodness knows there are other chores then needing my attention.

      So glad to see you here; come again.

  8. Eric : Gardenfork.tv says:

    Being the guy who hooks up an egg beater to his cordless drill – I like the wall-o-waters, and i use black plastic to heat the soil up in my raised beds.

    the black plastic really does make a difference, i measured it with my digital oven thermometer.

    Of course, I made a video of that too.

  9. Jane E. says:

    Great post!! Never thought of this.
    If you are planning to home-grow tomatoes this year, I highly recommend The Tomato Stake.


    Its easier to use than metal cages or towers, stronger than bamboo sticks, and wont rot or splinter like wood stakes.

    Happy Gardening!

    1. margaret says:

      Welcome, Jane E. Thanks for the tip–I know from our email that a friend of yours invented them, and that you are a “believer.” See you soon again I hope.

  10. themanicgardener says:

    Great post. It inspired my latest. I left you a message over at Blotanical to let you know, but it doesn’t look as if you hang out there much (don’t tell me–you’ve got a life?), so I’m repeating it here. Thanks!

  11. Kareen says:

    Hi Margaret ,
    Great meeting and assisting you today at Spring Garden Day . Yout talk was wonderful , thanks so much !
    I have great luck with tomatoes and so many plants by wintersowing . Go to the FAQ’s on this site, it explains it to those not familiar . http://forums2.gardenweb.com/forums/wtrsow/
    A lot less work than starting indoors and a very healthy plant.
    I hope to catch up with you again at your Open Days in May. Kareen

    1. margaret says:

      Welcome, Kareen. I really enjoyed the group today…to be around hundreds of other gardeners after such a long winter was great. I have wondered about this and am so happy to see local confirmation from you that it works. Thank you, and do come for Open Days 5/31.

  12. Betty says:

    I really enjoyed the tips for starting the tomatoes. This is a really great site and I apprecite the newsletter. Waht a lovely thing to do for all of us! Thank you and have a wonderful gardening season.

    1. margaret says:

      Welcome, Betty. How nice of you to comment and give me the feedback. I hope that we will spend part of the coming season together here; see you soon!

  13. eric : Gardenfork.tv says:

    my raised beds are still covered in snow, so i thought i’d try this: i covered the beds, and the snow, in black plastic ( and yes, i shot some video of it, to be posted soon )

    i did a control and left half a bed uncovered, i think it will melt the snow faster and heat the soil faster.

    thx again, eric. Gardenfork.tv, video podcast about Cooking, Gardening, and other fun stuff

    1. margaret says:

      Welcome, Gardenorganic. Makes sense when you think of it: commercial greenhouses have some kind of circulation going, and out in nature, the wind blows. :) Anyhow, see you soon again, I hope. Happy tomato-sowing meanwhile.

  14. Ken says:

    Whenever I start tomatoes from seed I always get some that germinate but have the baby leaves inside the seed when it breaks the surface. Eventually they just die. What causes this and is there anything I can do once it has happened?

    1. margaret says:

      Welcome, Ken. From what I understand, the more vigorously the tomatoes get started, the less likely this is to happen. I have occasionally had to mist the plant in this conditon and very gently knock the seed coat loose, but not so often. Are you growing a warm enough spot and with substantial light once the seeds break ground? I will try to do some homework as well. By the way, are these seeds you save or purchase each year?

  15. Ken says:

    Thank you for your response.
    The ones I used this year were new from Burpee. I used a 1/2 peat moss – 1/2 vermiculite starting mix. Placed them on top of the refrigerator in a slightly open plastic bag and set my home heating thermostat at 69 and on hold. My thinking was that being on top of the frig would hold the temp in the 70’s but I checked the minimum and maximum temps daily and it usually said the low was 68 and the high was 72. So I was struggling to keep in the 70’s. In about 6 days I noticed some started to come up in the morning and by that afternoon they were up. I put them under the grow light ASAP. About 3 of 18 had these little seed caps on them. I wondered if soaking them for a while before planting might help. I didn’t do that.

    1. margaret says:

      @Ken: I don’t soak them, either, but I do try to grow them warmer than that to really get them popping up strong. Maybe consider a heat mat for this step next year?

  16. Ken says:

    Thanks again Margaret. I am also trying to get some peppers to come up and they were not coming up. I started reading that they tend to need a warmer place than tomatoes and might take a while even at that. So I started to look for a warmer place. I have a light box on the ceiling over our cooking island in the kitchen with fluorescent bulbs. When I slid back one of the plastic panels it was quite warm up there. I checked the temperature and it was a steady 90. So the peppers found a new home. By the next morning they were peeking through. I had come up a few short of tomatoes so I put together another starting planter and put them up with the peppers. I’ll see if 90 is good for the tomatoes.
    Now I need to find that old fan and get it going on the plants that have been moved to the grow light. I’ve already been taking my hand or a wooden pencil and roughing them up a bit every day.
    Thanks again for the great advice.

  17. chigal says:

    My tomato seedlings are better than ever before, thanks to your tips. Just moved them into larger seedling pots over the weekend, and there was hardly any extra stem to bury. No leggy starts, this year! I had good light before, but no heat and no “petting.” I just saw a big start of the heirloom variety I like, at a grocery store, but my plants look much healthier. Thanks! Now, if I can just be patient enough to start hardening them off around Memorial Day…

  18. rock says:

    is it true once your tomato plant grows too fast you must cut the plant off at the top or the tomatoes will not grow before the harvest

    1. Margaret says:

      Hi, Jerry. Black walnuts exude chemicals from their roots that make the soil near them inhospitable to other plants, so many things will fail to thrive beneath or beside them. Read about it (which is called allelopathy) here.

  19. Nikki says:

    Hi Margaret: I’ve moved my tomato babies outside to a greenhouse because they seemed not to be thriving inside under my florescent plant lights. They were doing fine inside until I transplanted them into their own little containers. The containers have a mix of peat and my very own worm castings. That’s when I noticed their leaves were yellowing and kind of curling up on themselves. So out to the greenhouse they went. i checked weather.com’s historic feature and learned my night time temps don’t get above 50 degrees until June 14, so I can’t put them in their bed yet (even if I did the poor babies would probably be upset from all the rain we generally get until summer). Either way, they’re doing even worse in the greenhouse, they’ve got no new growth and are still yellow. I have some larger tomatoes in there too (they were a freebee from a hardware store) but those are doing fine.
    The varieties in my green house are Cherokee purples, yellow cherry, a Roma, a Beefsteak, and the Early Girls are the ones that are doing well. I also have several varieties of new world pepper seedlings in my greenhouse, they seem very happy. I have 4 types of basil in there as well, the lemon basil is upset about the move but the rest are fine and growing new leaves every day.
    The only thing I can think is that the worm castings are too rich, there insn’t much air flow, and I’ve changed how I’m watering them (the pots are in large reservoirs that I keep filled).
    Any advice would be much appreciated, thank you!
    I live at a higher elevation in the Pacific Northwest.

    1. Margaret says:

      Welcome, Nikki. I don’t know the answer with certainty, except to say that yes, too-wet soil will overwhelm young seedlings, as will too-rich soil, I think. Always best to start things in a sterile medium at first, meaning no additives beyond a seed-starting mix, and fertilize very lightly after they have true leaves and look like a baby plant of the kind you are expecting.

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