When to Start Seeds Indoors by Zone: Seed Starting Chart for Zones 4-9

October 13, 2026 · Around the house

Start seeds indoors by counting back from your average last frost date, not from your zone. Tomatoes go in about 52 days (roughly 7 weeks) before it, peppers and eggplant about 66 days before, onions and leeks about 122 days before, and cucumbers and squash only 17 days before. In Zone 6, using a reference last frost of Apr 20 (6a) or Apr 15 (6b), that puts the tomato start on Feb 27 or Feb 22. In Zone 7 it is Feb 17 or Feb 12; in Zone 5, Mar 9 or Mar 4. Full charts for zones 4 to 9 are below.

But read the next section before trusting any of those dates, including these.

Your zone is not your frost date

A USDA hardiness zone is built from one number: the average annual minimum winter temperature. It tells you whether a perennial survives your winter. It says nothing directly about when your last spring frost falls.

That is why published “last frost by zone” tables disagree. For Zone 6, the sources behind this post give last-frost dates anywhere from Apr 9 to May 15 - a spread of 36 days, more than 5 weeks. Zone 7 runs from Mar 18 to Apr 29 (42 days). A frost pocket, a north slope or higher ground runs late; a city lot or a south wall runs early. Two gardens in the same zone can be a month apart.

So the zone dates below are reference points. Look up your own average last frost date - in the US, search your ZIP code plus “frost dates” - and use the rule table to work out your own starts. It takes two minutes and is the single biggest improvement you can make to any seed starting calendar.

The formula

The simple version you see everywhere is:

indoor start date = last frost date - N weeks

The more careful version, which the charts here use, builds N per crop from four pieces:

1. Plant-out date. Frost-tolerant crops go out a set number of weeks before the average last frost (called LF50 here: the date with a 50% chance the last frost has passed). Frost-tender crops wait for LF10, the date with only a 10% chance of a later frost.
2. Minus 7 days of hardening off.
3. Minus the weeks the crop grows indoors (the middle of its usual range).
4. Minus the slow end of its germination range.

What falls out is a fixed number of days before LF50 for each crop. It is the same number in every zone - only the frost date moves.

These charts set LF10 at 18 days after LF50. If your local frost table gives a 10% date, use it for the tender crops instead.

Worked example: tomatoes in Zone 6a

Reference LF50 for Zone 6a: Apr 20.

• Tomatoes are tender, so they go out on LF10: Apr 20 + 18 days = May 8.
• Hardening off starts 7 days earlier: May 1.
• Seedlings need 7 weeks indoors (the middle of 6-8), so they must be up by Mar 13.
• Tomato seed can take up to 14 days to come up, so sow on Feb 27.

If your own LF50 turns out to be Apr 30, 10 days later than the reference, every date moves 10 days later: sow tomatoes on Mar 9. The gaps between the steps never change - they are what the plant needs.

Seed starting charts by zone

Each zone has two sub-zones with their own reference date. The “a” sub-zone is the colder half. “Prev. yr” means the arithmetic lands in the fall or winter before the spring you are planting for.

When to start seeds indoors, Zone 4

Published last-frost dates for Zone 4 run Apr 24 to May 12.

When to start seeds indoors, Zone 5

Published dates run Apr 7 to Apr 30.

Seed starting calendar, Zone 6

Published dates run Apr 9 to May 15 - the widest disagreement after Zone 7, so checking your local date matters most here.

When to start seeds indoors, Zone 7

Published dates run Mar 18 to Apr 29, a 42-day spread.

When to start seeds indoors, Zone 8

Published dates run Mar 13 to Mar 28.

When to start seeds indoors, Zone 9

Published dates run Feb 6 to Feb 28. This method assumes a spring plant-out after a last frost; in Zone 9 several starts land in the previous fall or winter, so treat this chart as the arithmetic, not a recommendation to grow every crop on that schedule.

The part most calendars get backwards: peppers before tomatoes

Look at the pepper and tomato rows in any zone. Peppers are sown 14 days before tomatoes, and planted out 7 days after them.

That is not a misprint. What sets the sowing date is total time from seed to garden. A pepper needs 9 weeks indoors (the middle of 8-10) and up to 21 days to germinate; a tomato needs 7 weeks and up to 14 days. The pepper’s extra 7-day wait for warm soil at the end does not make up the difference at the start.

The same logic runs the other way for cucumbers and squash: they get three weeks indoors and no more. They grow fast and resent root disturbance, so an older seedling is a worse plant, not a better one. Sowing them with the tomatoes is the classic mistake. And onions and leeks are the opposite extreme - about 17 weeks of lead, the first thing sown each season.

If you sow everything on one weekend, these differences are what go wrong.

How these were calculated

Frost dates. Reference last-frost dates per sub-zone come from one source, plantingcalendar.net, “Frost Dates by USDA Zone”, so that colder sub-zones always get later dates. The published ranges quoted for each zone combine it with SoilStack’s per-sub-zone planting calendars, Garden Design’s “First and Last Frost Dates” zone table, and WhenToPlant / The Ultimate Homestead sub-zone tables. These are approximate zone-wide averages, not measurements for any one garden, and they vary within every zone.

Crop timings. Germination days, weeks indoors and frost tolerance per crop are general seed-starting ranges from our own seed-starting guide, the same values the zone calendars below use. Your packet may differ for a given variety, and when it does, the packet wins - substitute its numbers into the four steps above. Dates use the slow end of germination, so if seed comes up early it waits a few days on the windowsill rather than missing its plant-out date.

Every date on this page was computed twice, by the code that generates the calendars and by a separate implementation of the four steps, and they agree to the day. This is a planning method, not a guarantee against frost; watch the forecast before planting out tender crops.

If you want this printed for your zone - both sub-zone calendars, a timeline of the indoor season, and an adjustment table that shifts every date to your own frost date - the Zone 6 planner is below.

The same planner for the other zones:

• Zone 4 seed starting calendar
• Zone 5 seed starting calendar
• Zone 7 seed starting calendar
• Zone 8 seed starting calendar
• Zone 9 seed starting calendar