When it's safe to plant tomatoes outside, zone by zone

Plant tomatoes outside about two weeks after your last spring frost, once nights stay above 50 °F. In most of the US that means somewhere between mid-April and late May, depending on your zone.

The last frost date is the start line, not the finish. Tomatoes survive cool nights, but cold soil and nights in the 40s stall them for weeks. A plant set out into warm soil two weeks later usually catches up and passes one that went in early.

Zone by zone

Zone	Average last frost	Start seeds indoors	Plant outside	First ripe fruit
4	Around May 12	Mid-March to mid-April	Late May to late June	August
5	Around April 30	Early March to early April	Mid-May to mid-June	Late July
6	Around April 21	Late February to late March	Early May to early June	Mid-July
7	Around April 3	Early February to early March	Mid-April to mid-May	Late June to July
8	Around March 28	Late January to late February	Mid-April to early May	Mid-June

The frost dates use the later end of each zone’s usual range, so they err on the safe side. Zones are drawn from winter low temperatures, not frost dates, so two gardens in the same zone can be weeks apart. If you know your own last frost date, count two weeks on from it. In the high country of zones 4 and 5, wait until June.

Three signs it’s time

1. The last frost is two weeks behind you. Check the 10-day forecast too.
2. Nights are above 50 °F. A few cool nights won’t hurt, but a run of them will.
3. The soil is warm. About 60 °F at 4 inches deep. Without a thermometer, wait until the soil feels warm to your hand in the morning.

Planting out

Harden plants off for a week first, putting them outside for longer each day. Then:

1. Choose a spot with at least eight hours of sun.
2. Dig in compost.
3. Plant deep, burying the stem up to the top few sets of leaves. Roots form all along the buried stem.
4. Space plants about 18 inches apart, in rows 2 feet apart. Give big indeterminate varieties more room.
5. Put in a stake or cage at the same time, so you don’t spear the roots later.
6. Water well, then mulch once the soil is warm.

Basil, marigolds and carrots are good neighbors. Keep tomatoes away from potatoes and sweet corn.

If you plant early

If you can’t wait, protect early plants:

• Wall of water or similar water-filled cloches keep plants several degrees warmer at night.
• Row cover over hoops gives a couple of degrees of frost protection.
• Black plastic laid over the bed for a week before planting warms the soil.

Cover plants whenever the forecast drops below about 38 °F, as frost forms at ground level before the air at thermometer height freezes.

Late planting

Tomatoes take 55 to 85 days from planting out to the first ripe fruit. In zones 4 and 5, don’t plant later than mid-June, and choose early or cherry varieties. In zones 7 and 8, a second planting in June gives fresh plants that crop into fall, after the first plants have tired in the heat.

For zone-specific detail, see tomatoes in zone 5 and tomatoes in zone 7. Choose your zone on the tomato page for the full calendar.