When to Plant Tomatoes

Tomatoes are a tender, warm-season crop - frost kills them outright, and even a cool, non-freezing night in the 40s stunts a young transplant's growth for a week or more. Timing tomatoes correctly means working backward from your zone's average last frost date, not from the calendar month.

Starting Seeds Indoors

Grow lights or a bright south-facing window both work for the indoor stretch. Seedlings started earlier than about 8 weeks before transplant time tend to get leggy and root-bound in their starter pots before it's actually safe to move them outside, which produces a weaker plant than one started on the right schedule - resist the temptation to start extra early just because you're eager to get going.

Transplanting Outdoors

Transplant only once nighttime temperatures are reliably staying above the low 50s Fahrenheit, which is typically 1-2 weeks after your zone's average last frost date, not right on it - tomatoes planted the moment frost risk technically clears often sit and sulk in cool soil for weeks, and a slightly later, warmer-soil transplant frequently catches up to and passes an anxious early one by midsummer. Hardening off transplants (gradually exposing them to outdoor conditions over 7-10 days before planting) matters more for tomatoes than for most other crops, since greenhouse- or windowsill-grown seedlings are notably more vulnerable to sunscald and wind stress than field-grown ones.

Succession and a Fall Crop

A second, later transplant 4-6 weeks after your main planting can extend your harvest window and provide a backup if the first round runs into disease pressure, though most home gardeners in shorter-season zones stick with one planting since tomatoes take the better part of a full season to mature.

Reading a Local Forecast Before You Transplant

Your zone's average last frost date is a long-term statistic, not a guarantee for this specific year - checking a real short-range forecast in the week before your planned transplant date is worth the two minutes it takes, and holding transplants indoors an extra few days if a late cold snap is forecast costs far less than losing a full flat of seedlings to one bad night.

Determinate vs. Indeterminate Changes the Harvest Shape

Determinate tomato varieties stop growing at a genetically fixed height and ripen most of their fruit within a shorter window, while indeterminate varieties keep growing and setting new fruit until frost - a distinction that matters for timing since determinate types suit a single concentrated harvest (canning, for instance) and indeterminate types suit the steady trickle most home gardeners actually want.