Zone 6 Planting Calendar: Every USDA Zone Dated

Step 1: Read what your zone number tells you

A hardiness zone is a winter-cold label. The USDA Plant Hardiness Zone Map is based on the average annual extreme minimum winter temperature, shown in 10-degree F zones from 1 to 13. Each zone splits into half zones, a and b, which are 5-degree F steps. So 6b is the warmer half of zone 6, and zone 8 without a letter is the whole band that holds 8a and 8b.

A New Mexico State University Extension circular puts the limit plainly. Zones help you choose plants that survive your winter, and picking those plants is only the first step. You then have to schedule planting so crops have time to mature.

A zone is a label for your winter low, and a planting date comes from the frost near you.

The dates come from frost records. Your last spring frost and first fall frost are the two numbers every sowing week is counted from.

Step 2: Look up the frost window for your zone

Extension services publish frost windows by state, so no single table covers the country. These rows come from five land-grant sources. The date ranges are averages, which Virginia Tech labels as a 50 percent chance.

The 4a row comes from Cornell Cooperative Extension in Hamilton County, the 5a and 5b rows from a New Mexico State circular, and the 6a to 8b rows from a Virginia Tech guide. The 9b row is a line from a UC Davis garden blog that says Davis, in zone 9b, has its last frost around March 1 and first frost around December 15.

The half zone matters less than you might expect. In Virginia, 6a and 6b share the same first fall frost, October 5 to 15, and their last spring frost differs by 10 days. The same New Mexico circular counts 126 frost-free days in zone 5a and 267 in zone 8b, a little more than double.

Same zone, different state

A zone does not give the same date in every state. Two land-grant tables list zones 6a through 8b, one for Virginia and one for New Mexico.

Take the table for the state you live in. If your state has none, use the nearest station and treat the zone as a rough guide only.

Step 3: Build your zone 6 planting calendar from the last frost

Zone 6b in Virginia has its last spring frost between April 25 and May 5. Count from the middle, April 30. Virginia Tech's crop dates then give peas a start of March 10, which is 51 days before. Carrots start March 20, 41 days before. Broccoli transplants go out April 1, 29 days before. Tomato transplants wait until May 10, 10 days after.

Tomatoes are the one crop everyone asks about. Virginia Tech sets the transplant window at May 10 to June 10 in zones 6a and 6b. A Montana State Extension guide says tomatoes reach transplant size in 6 to 10 weeks. Count back from May 10, and you start seeds indoors between March 1 and March 29.

Start seeds indoors in zone 6

Work back from the transplant dates in the table. The weeks a seedling needs to reach transplant size come from Montana State, and the dates come from Virginia Tech. The mix is mine, so treat the result as a window, not a rule.

Fall sowing runs on the other end of the calendar. In zone 6b, spinach and radish can go in until October 1, baby lettuce and mustard until September 20, and garlic from September 1 to October 1. These are Virginia's dates, so shift them if your first frost comes earlier or later.

The frost tables and countback charts in The Winter Plan do this same count for 24 cool-season and 15 warm-season crops from the last-frost date you write in.

Zone 7a to 8b planting guide: what moves with each half zone

Zone 7a runs from an April 15 to 25 last frost to an October 15 to 25 first frost in Virginia. Each half zone after that moves the spring windows earlier, as the table shows.

Zone 7a is colder than 7b. In the table, 7a tomato transplants start April 20, and 7b starts April 10.

Zone 3 to 5 and zone 9 to 11: planting schedule notes

Colder zones leave less room. Montana State Extension describes the limited season in Montana's zones 3 to 5. Its planting guide says to count the days between your two frost dates before you pick a crop. A tomato that needs 70 days after transplanting will not finish in a season shorter than that. Extension services publish frost dates by county or station, not for zone 3 as a whole, so use the county nearest you.

Warmer zones flip the problem. The University of Florida says frosts and freezes occur occasionally in Central Florida and rarely in South Florida, and that vegetables there can grow year-round if you pay attention to planting dates. In frost-free places such as these, your calendar runs on heat and the rainy season, not on frost.

Step 4: Check the window against your own yard

A table gives you a starting point. Your yard can run earlier or later.

The Virginia Tech guide says Roanoke County has four hardiness zones with a 30-day planting difference between them, and that south slopes run warmer and north slopes cooler. A New Mexico circular says individual gardens can vary as much as 20 days from the zone's average because of elevation, site exposure or air drainage.

A cold spring needs no new calendar. Virginia Tech says to favor earlier or later dates within a range based on local data or experience, and that row cover fabric and cold frames may extend the planting and harvest window by two to four weeks in spring and fall. Keep tomato and pepper seedlings in their trays until the date, and hold off the beans.

An early fall frost works the other way. The advice from Montana is to count the days between your two frost dates and compare them with the days to maturity on the packet. Pick the faster variety, or cover the bed.

So write down your own first and last frost each year, and shift your dates after two or three seasons. Plant tender crops after the date, not on it, because a 50 percent date means frost can still arrive the next week.

When your county's own calendar beats a zone table

If your state extension office publishes a calendar for your county, use that one. It was written by people who know your soil and your frost, and a table averaged over a whole zone cannot match it. Free printable calendars cover the basics too.

The Winter Plan fits when you want the sums done on paper and kept beside your garden notes. You pick the closest of its 108 stations, or write in your own date if none is near. Spring week jobs and the dates you write into the season calendar sit in the same file, and its notes for next winter page is where the first season's corrections go.