Tomatoes in zone 5 go out in mid-May, not a day sooner

Mid-May is the start of tomato planting in USDA zone 5. Transplant from mid-May to mid-June, after the last frost and once nights have stopped dipping below 50 °F, and start the seeds indoors from early March to early April.

Zone 5’s average last frost is around April 30 and the first fall frost comes around October 13. That leaves about five months, which is plenty for tomatoes as long as you don’t lose the start of it to a cold snap.

Why waiting pays

Tomatoes are tender. Any frost kills them, and soil below about 60 °F stalls them even without frost. A plant set out on a warm day in early May often sits still for two or three weeks, yellowing, while one planted in late May into warm soil grows straight away and catches up.

That’s the reason to plant by the soil rather than the calendar. If you have a soil thermometer, wait for 60 °F at 4 inches deep in the morning. If you don’t, wait until the overnight lows in the forecast are steadily in the 50s.

These dates are a starting point. A zone is set by how cold your winters get, not by frost dates, so your own last frost can be a couple of weeks either side. Gardens at altitude or in low, cold valleys run later. Towns near a large lake or in the middle of a city usually run earlier.

Starting seeds indoors

Sow from early March to early April, about six to eight weeks before you plan to plant out.

1. Sow seeds a quarter inch deep in small pots or cells of seed-starting mix.
2. Keep them warm, around 70 to 80 °F, until they come up. A heat mat helps.
3. Once they’re up, give them plenty of light. A shop light or grow light a few inches above the leaves for 14 to 16 hours a day stops them stretching.
4. Move them into 4-inch pots when they have their first true leaves.
5. Harden them off for a week before planting: a few hours outside in shelter, building up to a full day and night.

Bought transplants work just as well. Choose short, stocky plants with dark green leaves, not tall ones already in flower.

Planting out

Tomatoes are one of the few plants you can bury deeper than they grew in the pot. The buried stem grows roots, so the plant is sturdier and finds water more easily.

• Plant so only the top third of the plant is above the soil. Pull off any leaves that would end up buried.
• Space plants 18 inches apart in rows 2 feet apart, or one plant per square in square foot gardening.
• Put in a stake or cage at planting time. Tall varieties reach about 6 feet.
• Water well, then mulch once the soil has warmed.

Basil, marigolds, carrots and parsley grow well alongside. Keep tomatoes away from potatoes and sweet corn.

Getting the most from a short season

Tomatoes start ripening 55 to 85 days after transplanting, so in zone 5 the first fruit usually comes in late July. Picking runs until the first frost in mid-October.

Early, quick varieties make the most of that. Early Girl and cherry tomatoes such as Sungold ripen weeks before large beefsteaks. If you love big tomatoes, grow one or two and fill the rest of the space with quicker kinds.

Row cover or water-filled cloches let you plant a week or two earlier with less risk. They also hold warmth on the first cold nights of fall.

When frost is forecast in October, pick every tomato that has started to change color. They finish ripening on a kitchen counter. Fully green fruit rarely ripens well, but makes good chutney or fried green tomatoes.

Common problems

Blossom end rot. A dark, sunken patch at the bottom of the fruit. It’s caused by uneven watering more than by a lack of calcium in the soil. Water deeply and regularly, and mulch to keep the soil evenly moist.

Yellow lower leaves. Often early blight, a fungus that splashes up from the soil. Mulch, water at the base, and remove affected leaves.

Cracked fruit. A heavy rain after a dry spell. Even watering helps here too.

Open the tomato page and pick zone 5 from the frost menu to see every window on one chart.