Vegetable Seed Guide: When to Start Seeds Indoors
By Steven Biggs
When to Plant Vegetables
Not sure when to start planting seeds indoors?
If you time planting well, your seedlings will be big enough to survive transplanting into the garden.
But don’t start seeds indoors too early: Earlier planting and bigger seedlings is not always better.
That’s because a seedling that’s stuck in a pot for too long, waiting to go into the garden, gets stressed. And sometimes stressed transplants don’t bounce back, even once you plant them into the garden.
(Late in the planting season big box stores often have discounted transplants: wilted, root-bound cauliflower, cucumber, and chard that have simply run out of steam…don’t be tempted!)
If you’re wondering when to start seedlings indoors, keep reading. This guide tells you when to sow seeds—and how to know when to sow seeds.
Why Start Seedlings Indoors
Start seedlings indoors to get a jump start on the season and to protect them from weather and pests.
There are two main reasons to start seeds indoors.
In cold climates, season length limits harvests—and starting seeds indoors give a longer window of growth for the crop
Indoors, we can control conditions and prevent pest damage, giving small seedlings a chance to get started at a suitable temperature, without getting mown down by bugs
When to Start Seeds Indoors
Luckily, vegetable seeds don’t all have to be planted at the same time. You can spread out seed sowing from mid winter through spring—when you start sowing some seeds directly in the garden.
The guidepost for choosing when to start planting seeds indoors is something called the average last frost date—or simply “last frost date.” This is the average date of the last spring frost in your area. (It’s an average, so some years there is a frost following this date.)
If you don’t know your average last frost date, a good place to start is by asking local gardeners, or checking with local seed vendors.
Work Backwards from the Average Last Frost Date
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Once you have your last frost date, you just work backwards to get the sowing date for all of your different vegetable seeds.
It’s your guidepost.
Workback: When to Plant Vegetables
Below is how many weeks before the last frost date I sow my vegetable seeds.
Keep in mind that none of this is cast in stone. You have a window of time for seed sowing. It doesn’t have to happen in one specific week.
That means that if you miss the mark with your celery seeds, and forget to sow them at 10 weeks, don’t sweat it. Sow them at 9 weeks, and your celery transplants might just be a bit smaller when you put them into the garden.
This list is a work in progress. If you have a favourite vegetable crop that’s not on here, e-mail me.
10 Weeks Before Last Spring Frost
Leek seed are some of the first seeds that I plant indoors, 10 weeks before the last frost date in the spring.
Indoors
These are the first vegetable seeds that I start indoors, under lights.
celery, eggplant, leek, onion, pepper, parsley
8 Weeks Before Last Spring Frost
Indoors
tomato
7 Weeks Before Last Spring Frost
Indoors
more tomatoes (we like our tomatoes here in the Biggs household!)
6 Weeks Before Last Spring Frost
Indoors
lettuce, cabbage family (broccoli, cauliflower, Brussels sprouts, kohlrabi, kale)
Direct-Seed in the Garden
Direct-seeding carrot seeds in the garden 6 weeks before the last frost date.
This is also when I start to direct-seed some cold-tolerant vegetable crops in the garden. These include:
broad bean, carrot, pea, spinach, lettuce, turnip, dill, parsley
Plant or Transplant in the Garden
plant onion sets (small, pre-grown onion bulbs), and transplant onion seedlings
4 Weeks Before Last Spring Frost
Indoors
melon, basil, cucumber, squash, pumpkin
Direct-Seed in the Garden
radish, beet, chard, more lettuce
Plant or Transplant in the Garden
cabbage family seedlings
seed potatoes
2 Weeks Before Last Spring Frost
Direct-Seed in the Garden
corn, cheater beans*
*With beans, we usually wait until the soil is warm and there’s no further risk of frost. That’s because bean seeds can rot in cold, wet soil—and if young bean plants get hit by frost, they’ll die. But some years are warmer than others, and if it seems warm, I like to cheat and get in an early row of “cheater beans.” If they do well, I get beans sooner. (If they get nipped by frost, no big loss; I’ll just replant.)
Plant or Transplant in the Garden
lettuce
gladiolus bulbs (I know…they’re not a veggie, but I like to grow this cut flower in my veggie garden, reminds me of Grandma Q)
The Week of the Last Spring Frost
Wait until 1-2 weeks after the last frost date before transplanting pepper seedlings into the garden. They HATE the cold!
Direct-Seed in the Garden
beans, cauliflower, cucumber, squash
Transplant in the Garden
tomato (some people plant tomatoes a week or two after the last frost date…I’m impatient, so I plant them, but protect them as needed)
1-2 Weeks Following the Last Spring Frost
Direct-Seed in the Garden
Now it’s time to direct seed the cold-hating crops!
lima bean, edamame, melon, basil
Plant or Transplant in the Garden
Make sure the temperature will be over 10°C at night
celery, melon, pepper, eggplant
sweet potato slips
There are some crops that I start indoors, and also sow directly in the garden later. These cucumbers are sown directly in the garden.
You might notice that some crops, such as melon and basil, are in my list above twice: seeded indoors, and then directly sown outdoors. That’s because you can do it both ways, and having the same crop in two stages of development can give you a longer harvest window.
Make Successive Plantings
Don’t forget that after the initial planting of many of these crops, you can make successive plantings so that you have an ongoing harvest. That means after your first sowing of beet seeds, make more, at two-week intervals. Same with carrots, and leafy greens.
How to Stay Organized
If you’ve looked at my planting dates above, you might be wondering if there’s a simple way to stay organized.
There is!
I sort my seed packets by starting date. I’m a visual person—so no spreadsheets for me!
Seed packets organized by planting date, so that I don’t forget to plant anything!
I simply make stacks of seed packets, organized by when they should be planted. Then, I mark my calendar for the various seed-starting dates—flagging 10 weeks, 8 weeks, 6 weeks, etc.
When the given week rolls around, I grab the seed packets for that week.
