✳ Guide · Grow Axis

When to plant: building a planting calendar from your zip code, your frost dates, and your summer

10 minute read · Published 7 September 2026 · All guides

The back of a seed packet says "sow after all danger of frost". That is true and nearly useless, because the date it points to depends on where you stand, and in half the country the frost is not even the constraint that matters. This guide builds a planting calendar the way Grow Axis builds one: from your location outward.

1. Start with the zone, then stop trusting it

The USDA Plant Hardiness Zone Map divides the country into zones by average annual minimum winter temperature, in 10 degree Fahrenheit bands with 5 degree half-zones. Your zone tells you which perennials survive your winter. It is a rough proxy for frost dates and nothing more. Two gardens in the same zone can be three weeks apart on last frost because of elevation, a lake, or a north-facing slope.

Grow Axis looks up a zone from your zip code and uses it as a starting estimate for frost dates. It is an estimate, and the app says so: you can override the frost dates by hand, and after you have logged when frost actually hit for two seasons, your own plot's history outranks the zone table.

2. Get the two dates that anchor everything

A planting calendar hangs on two dates: the average last spring frost and the average first fall frost. Everything cool-season is timed off the first; everything that has to finish before winter is timed off the second. Your state extension service publishes these by county or city, and they are averages, so half of years the frost comes later than the date.

The practical rule: treat the last-frost date as the earliest you would gamble a warm-season crop, not the day you plant it. Give it a week or two of margin unless you have row cover ready.

3. Count backwards with days to maturity

Every variety has a days-to-maturity number, the time from sowing or transplanting to first harvest. Fall planting is the calculation people get wrong: take the first fall frost date, subtract the days to maturity, then subtract another two weeks for the "fall factor", because plants grow more slowly as days shorten and cool. That is your last sowing date for that crop.

Grow Axis computes every milestone date from the variety's days to maturity and your frost dates, rather than storing dates. That matters when you correct a number: fix the days to maturity once and every plan built on it updates. You can photograph the seed packet and the app reads the variety's days to maturity off it, so the plan is built on your packet, not a generic crop average.

4. In the hot South, summer is the wall, not frost

In USDA zones 8 and 9, which cover the Gulf South from Texas across to the Carolinas, the growing season is long and the frost dates are generous. The binding constraint is heat. Lettuce bolts, broccoli buttons, tomatoes stop setting fruit once nights stay warm. A frost-only calendar will happily tell you to sow spring broccoli in April, and the heat will finish it before it finishes you a head.

The LSU AgCenter vegetable planting guide is the reference for the region and it is organised around this reality: spring cool-season crops are bounded by summer, not by frost, and many warm-season crops have a second, fall window. Grow Axis carries a regional overlay for the Gulf South with a summer blackout from June 1 to August 10, when it will not schedule new sowings of most crops, plus per-crop windows sourced from LSU with the citation shown in the app. One rule the app follows that a naive model gets wrong: an explicit regional window wins over the generic heat blackout, which is what makes fall tomatoes possible.

5. Succession: the same crop, every two or three weeks

If you sow a whole bed of lettuce on one day you get a whole bed of lettuce on one day. Succession sowing means a short row every two to three weeks so the harvest arrives steadily. It applies to lettuce, radishes, beans, cilantro, beets and most quick crops. The calendar work is tedious by hand, which is why nobody does it. In Grow Axis one tap adds every round that still finishes this season, each on the week it belongs to.

6. When you are late

You will be late. Life happens in March. The question is not "am I behind" but "what still finishes". For a spring cool-season crop, the answer depends on whether it can mature before the heat arrives, which is a different calculation from the frost one and the reason late spring is so unforgiving in the South. Grow Axis has a replanner for this: when a sowing date has passed, it shows what still finishes in your window and what to swap in or save for fall.

7. Turn the season into this week

A season plan is hundreds of details. You do not garden a season; you garden a Saturday. The weekly view should show only the sowing, transplanting and harvesting that belongs to the next seven days, with the rest a click away. Print it and take it outside. Grow Axis turns the plan into a short weekly job list, skips the watering when rain is forecast, prints the season to a single sheet for the garden, and installs on your phone like an app.

8. Keep records that make next year easier

Three things worth writing down every season: the date frost actually came, what did well in which bed, and what you would not plant again. The first one improves your calendar. The second one drives crop rotation, which is the cheapest disease control there is. The third one saves money. Grow Axis keeps a journal and harvest log per planting and rotates crops bed by bed.

The short version

• Zone gives you an estimate. Your own frost log gives you the truth.
• Spring crops count forward from last frost. Fall crops count back from first frost, plus two weeks.
• In zones 8 and 9, plan around the heat. Many crops have a fall window that is better than spring.
• Sow a little every two to three weeks instead of everything at once.
• Plan the season, work the week.

Sources

• USDA Plant Hardiness Zone Map
• LSU AgCenter, Louisiana Vegetable Planting Guide (Pub. 1980)
• LSU AgCenter, When to Plant: Louisiana Garden Planting Chart