When to Start Seeds by Zone (USDA Sowing Calendar)

Written & researched by Elena Marsh Gardening & Landscaping Editor

Updated October 2026

The short answer: find your average last spring frost date, then count backward — 10 to 12 weeks for onions and leeks, 8 to 10 for peppers and eggplant, 6 to 8 for tomatoes, 4 to 6 for broccoli, cabbage and lettuce, and just 2 to 4 for cucumbers, squash and melons. In zone 6, where the last frost averages April 21, that means peppers around February 10, tomatoes around March 1, brassicas around March 17 and squash around April 1. The full tables are below.

First, a Correction Worth Making

A USDA hardiness zone is not a frost date. Zones are calculated from the average annual minimum winter temperature and exist to tell you whether a perennial will survive your winter. Seattle and Dallas are both broadly zone 8, but Dallas is done with frost weeks before Seattle is. Elevation, proximity to large water, and whether your yard sits in a low frost pocket all shift the real date.

So use the zone table below as a starting point, then check your actual date. NOAA publishes freeze-date probabilities by station, and every state cooperative extension service publishes last-frost dates by county or ZIP code. If you have gardened the same yard for a few years, your own records beat all of it.

Average Frost Dates by USDA Zone

These are averages, which means roughly half of all years bring a frost after the listed date. If you want to plant tender crops on the average date, be ready to throw a sheet or a cloche over them on the one clear, still night that catches everybody out.

How Many Weeks Before Last Frost to Sow

This is the number that turns a frost date into a sowing date. The third column is just as important — it tells you when the seedling actually goes outside, which is what the indoor weeks are working toward.

The bottom four rows are not a stylistic preference — those crops either grow a taproot that forks permanently when disturbed or germinate so readily in warm soil that a tray is wasted work. The reasoning crop by crop is in direct sow vs transplant.

Indoor Sowing Dates, Zone by Zone

Applying those intervals to the average last frost dates gives the following windows. Use the later half of each window if this is your first year — late seedlings catch up, overgrown ones do not.

Gardeners in zones 9 and 10 should read that table with one adjustment: your limiting factor in summer is heat, not frost. Tomatoes stop setting fruit once nights stay above about 75°F, so the goal there is to have plants flowering before that heat arrives — and then to plant a second crop in late summer for a fall harvest, which northern gardeners cannot do at all.

The Calendar Nobody Uses: Counting Back from First Frost

Spring sowing dates count forward from the last frost. A fall garden counts backward from the first one, and the arithmetic has an extra step. Take the days to maturity on the packet, add about 14 days because plants grow more slowly under the shortening days of autumn, add a further 14 days if you want a harvest window rather than a single picking, and count back from your first frost date.

For a zone 6 gardener with a first frost around October 20, that puts a 55-day bush bean sowing at roughly August 1 and a 60-day broccoli transplant at roughly July 25. Frost-hardy crops — kale, spinach, leeks, carrots, Brussels sprouts — can be sown later still, because a light frost improves them rather than ending them. That second season is the part of succession planting most gardens leave on the table.

A Worked Example

Zone 6, average last frost April 21, first frost October 20. Around February 10 the peppers and eggplant go into cells on a heat mat. February 24, tomatoes. March 10, broccoli, cabbage and lettuce. March 24, cucumbers and squash — and the brassicas, now four weeks old, start hardening off. Early April, hardened brassicas, lettuce and onions go into the bed; peas, spinach, carrots and radishes are direct sown. April 21, tomatoes go out under cover if the forecast is unsettled. Early May, peppers, eggplant, basil, cucumbers, squash and beans — once soil is genuinely at 65°F.

Two things make that schedule work. The first is not sowing everything on the same weekend, which is the temptation in February. The second is hardening off properly at each stage, because every date above assumes a plant that can survive the move — the routine is in hardening off seedlings.

What This Requires Indoors

A February sowing date in zone 5 or 6 means eight to ten weeks of indoor growing in the darkest part of the year, and that is where most schedules quietly fail. Seedlings held that long on a windowsill stretch, pale and flop — see why seedlings get leggy for the fix. A timer-controlled light 2 to 4 inches above the tray for 14 to 16 hours a day is what makes an early sowing date worth having; without it, sowing later actually produces better plants. Tray and dome options are covered in our best seed starting kits, and the fixtures themselves in best grow lights for indoor plants.

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