When to Start Seeds Indoors: A Week-by-Week Schedule

Seed starting dates are counted backward from your average last spring frost. Slow growers like onions and peppers start 10 to 12 weeks ahead; fast growers like cucumbers and squash start only 2 to 3 weeks ahead. Start too late and plants aren’t ready; start too early and they get leggy and root-bound before it’s warm enough to plant.

First, look up your date with Frost Dates by ZIP Code. Then use the schedule below, or let the Seed Starting Calculator work out the exact dates.

Seed starting chart

Crop	Sow indoors	Plant outside
Onions (from seed)	10–12 weeks before last frost	2–4 weeks before last frost
Peppers	8–10 weeks before	2–3 weeks after
Eggplant	8–10 weeks before	2–3 weeks after
Tomatoes	6–8 weeks before	1–2 weeks after
Basil	5–6 weeks before	1–2 weeks after
Cucumbers	2–3 weeks before	1–2 weeks after
Summer squash and zucchini	2–3 weeks before	1–2 weeks after

Planting-out dates for warm-season crops assume nights have warmed to about 50°F. Check the forecast rather than the calendar.

Week-by-week schedule

Count back from your last frost date. “Week 0” is the frost date itself.

12 to 10 weeks before last frost

Sow onions from seed. Trim the tops to about 3 inches whenever they flop over; it keeps them sturdy.
Check that your lights, trays and seed starting mix are ready.

10 to 8 weeks before

Sow peppers and eggplant. Both germinate slowly in cool rooms; a heat mat that keeps the mix at 75 to 80°F speeds them up a lot.

8 to 6 weeks before

Sow tomatoes. They germinate in 5 to 10 days at room temperature.
Move peppers and eggplant into bigger pots once they have their first true leaves.

6 to 5 weeks before

Sow basil. It is slow to germinate, so give it warmth.
Pot up tomatoes when they have two sets of true leaves. Bury the stem a little deeper each time.

4 to 3 weeks before

Start hardening off onions, which go out early.

3 to 2 weeks before

Sow cucumbers and summer squash in individual pots. Their roots dislike being disturbed, so avoid sowing them in shared trays; 3 to 5 weeks indoors is plenty.

2 weeks before to last frost

Plant onions outside.
Begin hardening off the other seedlings: a few hours outdoors in a sheltered spot at first, more sun and time each day for about a week.

1 to 3 weeks after last frost

Plant out tomatoes, basil, cucumbers and squash once nights stay above 50°F.
Plant peppers and eggplant last; they sulk in cold soil.

Crops to sow directly outside

Some crops grow so fast, or dislike transplanting so much, that it’s easier to sow them where they will grow:

Beans, corn and squash after the last frost, once the soil is warm.
Peas, spinach, lettuce, radishes and carrots a few weeks before the last frost; they tolerate cool weather.

Setting up for success

Use seed starting mix, not garden soil. It is light, sterile and drains well.
Give plenty of light. A sunny window is rarely enough in late winter. Hang LED shop lights or grow lights a few inches above the seedlings and run them 14 to 16 hours a day. Raise them as the plants grow.
Water from below. Set trays in a little water for 20 minutes rather than pouring over the top. It keeps seedlings drier and helps prevent damping-off disease.
Move air. A small fan on low makes stems stronger and discourages mold.
Feed lightly. Once seedlings have true leaves, use a diluted liquid fertilizer every week or two.

Early or late in the window?

Each crop has a 2-week sowing window. Use the start of the window if you grow under strong lights and plan to pot up into large containers. Use the end of the window if you rely on a windowsill, have little space, or live where spring is often cool and wet. Smaller, younger transplants usually catch up quickly once they are in the ground.