When to start seeds indoors

Indoor seed starting is simple arithmetic: count back a set number of weeks from your last frost. Enter your ZIP, or drag the frost date yourself, and every start date updates.

Count backwards from frost

FebMarAprMayOnionsPeppersEggplantBroccoliCabbageCauliflowerBrussels sproutsTomatoesKaleLettuceBasilZucchiniWinter squashPumpkinsWatermelonCucumbers
  • Start indoors
  • Transplant outside
  • Last frost

Your seed starting dates

CropStart indoorsTransplantStatus
OnionsJan 26 – Feb 9Mar 23 – Apr 6
PeppersFeb 9–23May 4–18
EggplantFeb 9–23May 4–18
BroccoliFeb 9 – Mar 9Apr 6–20
CabbageFeb 9–23Mar 23 – Apr 6
CauliflowerFeb 9–23Apr 6–20
Brussels sproutsFeb 9–23Apr 6–20
TomatoesFeb 23 – Mar 9Apr 27 – May 11
KaleFeb 23 – Mar 9Mar 23 – Apr 6
LettuceMar 9–23Apr 6–20
BasilMar 9–23May 4–11
ZucchiniMar 23–30May 4–11
Winter squashMar 23–30May 4–11
PumpkinsMar 23–30May 4–18
WatermelonMar 23 – Apr 6May 4–18
CucumbersMar 30 – Apr 6May 4–11

Why the weeks differ so much

The weeks-before-frost figure is how long a seedling takes to reach transplant size, plus a week of hardening off. Onions grow slowly from a tiny seed, so they need 10–12 weeks. Peppers are slow to germinate and grow, so 8–10. Tomatoes grow fast and are ready in 6–8. Squash and cucumbers grow so quickly that starting more than 3–4 weeks ahead just gives you a root-bound plant.

The transplant date then depends on frost tolerance: cabbage family and onion seedlings go out before the last frost, while tomatoes and peppers wait until after, when nights stay above 50°F.

Hardening off

Seedlings raised indoors have never felt wind or direct sun. Over 7–10 days, set them outside for a few hours, then longer, bringing them in on cold nights. Skipping this is the most common reason healthy seedlings stall or scorch after transplanting.

Seed starting FAQ

When should I start seeds indoors?

Count back from your last frost date. Onions and leeks start 10–12 weeks before it, peppers and eggplant 8–10 weeks, tomatoes 6–8 weeks, lettuce and brassicas 4–8 weeks, and cucumbers, squash and melons only 2–4 weeks before.

What happens if I start seeds too early?

Seedlings outgrow their pots, become leggy and root-bound, and often transplant worse than younger plants. A tomato started 12 weeks early is usually no earlier to fruit than one started at 7 weeks.

Which vegetables should not be started indoors?

Root crops such as carrots, beets, radishes and parsnips, plus peas, beans and corn, grow best sown directly in the garden. Their roots dislike transplanting and they grow quickly outdoors.

Do I need grow lights to start seeds?

A sunny windowsill rarely gives enough light in late winter, so seedlings stretch. An inexpensive LED shop light kept 2–4 inches above the plants for 14–16 hours a day works well.