when to start what: vegetable-seed calculators

seed starting 2WONDER WHAT TO SOW WHEN to get homegrown transplants ready for the vegetable garden? I’ve gathered links to some foolproof online seed-starting calculators and charts, and also summarized my very simple “lumping” method, where I group all my seeds into three groups rather than try to remember every last detail of what happens when. The scoop:

Margaret's seed-starting calculator

charts and calculators

Cellpack of young tomato seedlings ready for transplant.

my ‘lumping’ method of when to sow

BY LUMPING THE CROPS I SOW INDOORS in spring into three simple groups with similar time needs, I streamline my seed-starting. You’ll need to memorize only one fact to use my “lumped-together” countdown formula, and that’s your local date of average final frost (mine isn’t until close to June).

The brassicas, like broccoli, Brussels sprouts, cabbage, cauliflower and kohlrabi, all have the same requirements: a month to six weeks indoors under lights before they go outside, which is safe about a month before final frost. This group therefore gets its start between March 15 and April 1 in my household. (Note with Brussels sprouts: many resources say sow them later, like May 1 or so, so they stand well into frost, when they achieve their best flavor. Today there are varieties requiring as few as 82ish days to maturity and as many as 100-plus, so take into consideration which you’re growing when you plan when to sow.)

Tomatoes, peppers and eggplants make up my second group, each getting six to eight weeks under lights before transplanting, when all frost danger is past. Early to mid-April is my target sowing date, therefore—a friend nearby makes it even simpler, and says to sow your tomatoes at tax time.

The last group: the big-seeded sorts like pumpkins, squash, melons and cucumbers, which only need a couple of weeks indoors (or if you think you can outsmart the chipmunks, who usually take the seeds at my place, just direct sow around your frost date). Inside, I start these in mid-May or so.

Speaking of what else to sow outdoors…everyone differs on that. Things I prefer to direct sow because it’s so easy include salad greens (lettuce, arugula and such); peas (as soon as the soil can be worked, about mid-March here); and spinach (either late fall for an extra-early crop, or very early spring); chard; broccoli raab; beets and other root crops; kales and collards; dill, and beans.

With the greens, there’s a tradeoff some years to direct-sowing, especially for me with the leafy brassicas (the kale and collards), which can coincide sometimes with an upsurge in flea beetles, who eat tiny holes in things (they love arugula, too). Sometimes starting the plants indoors can outsmart the flea beetles, but growing them under a floating row cover will help, too. I never start peas or beans indoors; the rest I sometimes do, again, to cope with pests.

I often buy my onions as plants, since they take 8-10 weeks indoors, but you can sow indoors, too (I would have done so in February for an April set-out).

Basil and parsley, two other staples, fit into the system, parsley with the early stuff, basil with the later.

Experts who disagree and say eggplants actually need a week or two longer indoors (like eight) than tomatoes and go outdoors a week later, for instance. They’re right, in the best of worlds. But lumping is simpler, and since no two weather years are alike—particularly no two springs—I expect there’s a kind of built-in balancing act going on outdoors, anyhow.

How to sow indoors, in a simple slideshow.

  1. cyra says:

    Hi Margaret,
    New gardener question – how does seed starting work with succession planting? Is that only for seeds that you direct sow? Looking for a chart and/or web resource that lays out how and when to plant various plants.

  2. Terryk says:

    Thanks for the charts you linked Margaret.

    I started last night. The soil smelled so good. I may be late but I started some artichokes along with brussel sprouts, brocolli and lettuces. God I am glad I took your advise on the pelletized lettuce seed, what a difference!

    I think the artichokes are the annual ones vs. the regular. So confusing as I read to start 8 weeks before last frost date. If this is correct, I think I am OK. But then I think you still need to set them out when temps are in 50s so they set buds. Anyone care to set me straight?

    My frustration is that many of the seed packs don’t tell you what temperature to have specific seed germinate and how long it takes for germination. Margaret, or anyone out there, have a chart? I pulled out my Johnny’s seed catalog and on some they have this info and then on some they don’t. Frustrating as it has been a while since I have done veggies and I feel like a newbie here.

  3. Terryk says:

    Well after doing a search I came up with this website which gives some of the vegetables, the temps they germinate at and days to germinate.

    I thought I would share just in case someone else is in need of the info.


    Of course any tips on artichokes would be appreciated (especially if you are in a cold area). I have never grown them, but would love to have success.

  4. Naseer says:

    Hi Margaret, long time!

    Great post, as always, but I had one little question. You grouped the brussel sprouts in with the other brassicas for an early start, but this conflicted with the directions I found on the HV Seed Library site for the brussel sprouts seeds we got from them:
    “Start seedlings in May–no earlier. Too-early crops reach maturity before the hard frosts arrive that make them so delicious, and it sometimes proves difficult to pull mature plants along an extra month until frost season. ”
    Have you ever noticed this to be the case, and have you ever tried growing them with your tomato lump instead?

    Good luck with your seed starting this year! Based on your advice, we’re trying out APS for the first time, and it seems great so far.

    1. Margaret says:

      Hi, Naseer. Yes, I usually do them both times, and later is easier as they say — and you do get the benefit of the cold to make them tastier. I really love them, and pick them from early fall onward, including some that haven’t been frosted. I should make a notation of this in the story; very good point. There are now varieties requiring from 80+ to 100+ days from seed to harvest, which further complicates when to do what…but listen to HVSL for the one you bought from them. The chart I love from Maine Organic Growers says April 1, so I am not alone in my madness. :) And thanks for suggesting a good edit to clarify!

  5. Stacy M says:

    Thank you thank you! I have been wondering when to start my peppers and was about to do it this weekend, but it’s too early. You saved me!

    It really is hard to wait when the sun is shining

  6. David says:

    We just started our three types of Roma tomatoes in damp paper towel on a little heat mat. It is still pretty darn cold here in Michigan, so outdoor tomato planting seems a ways away right now… but I always regret not getting my seedlings going under lights by early April…

  7. Kathy from Cold Climate Gardening says:

    Did you really already sow your peas? We haven’t heard peepers yet, which is when we like to sow ours. Also the soil has re-frozen, at least the top layer.

    1. Margaret says:

      I did sow them, Kathy. It was crazy warm and I went for it. Then everything froze. We shall see what happens! I had leftover (but still viable) seed from year before last, so I was feeling like trying…and I have enough still in reserve to try again. Maybe the chipmunks will eat this first batch and not the next one. :)

  8. Susan says:

    Quick question, how can I find my last and first frost date as an expat in Europe? I’m in the suburbs of Paris and I could handle it in French, but I havent found anything like that (date de dernière gelée?) in the books or blogs I’ve been reading. Plus I’d feel a bit safer in English.

  9. Susan says:

    Hi Margaret, thanks for the help, I did stumble across that one before (and there’s a similar hardiness zone chart on wikipedia) but nothing seems to talk about last frost. I’m just going to risk planting things a bit early and keep an eye on the weather but it’s so strange to me how something so fundamental to US and Canada gardening isnt even mentioned over here, and I do read French gardening books.

  10. Jen says:

    I’ve been gardening for several years, but we just bought our first house and there’s two yards that are calling to me to cultivate with something other than lawn.
    I have a hankering to start growing more Veg and your “lumping” technique of when to start seeds is AWESOME! Thanks!
    Also…the calculators and other tips are very helpful. If I lived closer, I’d invite you over for homegrown Lemon Verbena Tea!

    1. margaret says:

      Glad you like the “lumping” idea, Jen. It just makes it easier for me to not get overwhelmed on all the details! See you soon I hope.

  11. Jen says:

    I have a quick question- in my zone of CT it says the last average frost risk is April 30 but then it says May 18 is the guaranteed frost-free date. Which one should I use to count backward? I started with the April 30 one but now I’m not sure if that is right.

  12. Jean Schember says:

    so I have had this discussion over nad over with my husband and he seems to think
    that I am crazy for wanting to plant my peppers and tomatoes already. I think last year I planted my tomatoes in mid Feb but he says no mid April for them. What is your take on planting of them in the 49677 zone

    1. margaret says:

      Hi, Jean. Put your last frost date into my calculator tool to figure out. Start here. (If you don’t know your last frost the instructions on top of that page tell you where to get it.) I think your zip code is Michigan, so I am guessing April sometime is right.

  13. Vanessa says:

    I LOVE this! I have always wanted my own garden but I have no idea how to begin. I found your site SO helpful and “beginner” friendly :)

  14. christine says:

    Hello, thank you for your wonderful post. I have a damage control question. I started everything I have indoors at the end of Feb (peas, peppers, tomatoes, squash, peppers, zucchini, lettuce) for a horticulture therapy program at work. They’ve all grown very tall and spindly and I am quickly running out of room in the dining room where they grow. Are they doomed? How can I slow them down and potentially encourage them to stop growing up and maybe start thickening a bit?

    1. margaret says:

      Hi, Christine. Much too early if you live in the North — and I’m afraid there is no remedy usually. You don’t mention where you are located so I am at a loss to advise. Also: peas should be direct-sown in the garden; don’t try to transplant.

  15. Sally K. says:

    We started San Marzano tomatoes indoors, and they look fragile. We just put them in the ground, and it’s May 15th here in the mountains of San Diego County, CA. We have had crazy weather for 2014, and hope we have not planted the wrong variety of tomatoes. I do like your “lumping system”. It makes the process a bit easier. Thanks for a great post!

  16. Emily says:

    I’m a first-time gardener in northern Illinois trying out a raised bed and I just planted everything at the same time yesterday. I planted bean seeds and basil seeds, but transplanted everything else: pepper, tomato, cauliflower, zucchini, cucumber, and marigold. Of course I didn’t do enough research and I’ve realized that I’m a couple of weeks early for the peppers, tomatoes, zucchinis and cucumbers. The next few days are supposed to get cold at night (low of 35 tonight, 37 Friday night and 39 Saturday night). Even during the day it is just going to be in the 50s. Next week it warms up, but just to 60s and low 70s.

    My question is have I basically just wasted a lot of time and money? Should I dig up some plants and try to bring them back inside? Would covering them somehow save them?


    1. margaret says:

      Hi, Emily. I would have covered the tender things like peppers, tomatoes, zuke, cuke, marigold at least if they were out so early, yes. I wouldn’t worry about the seeds so much. The only comfort is that I think this year in confounding everyone as to timing, but generally int he North I like to consider Memorial Day or even early June as the OK time for tender things liek tomatoes to go outside, so start by counting back next year from a safer date.

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