USDA Zone 4

Average annual extreme minimum temperature: -30 to -20°F

Move one zone up from Zone 3's brutal 90-day squeeze and the picture changes: Zone 4 gives a real, workable growing season, though frost on both ends is still close enough that timing matters more than it would further south. USDA's 2023 hardiness map puts this band's average extreme minimum winter temperature at -30 to -20 Fahrenheit, running through much of the upper Midwest (Minnesota, Wisconsin, Michigan's Upper Peninsula), interior New England including Vermont and New Hampshire, and mid-elevation mountain valleys across the Rockies and Intermountain West.

Typical Frost Window

Mid-to-late May is when the average last spring frost lands here per NOAA/NCEI's long-term data, with the average first fall frost following in the last week of September to the first week of October - roughly 125 to 140 frost-free days most years. These are historical averages, never a forecast for a specific year; both a late-May frost and an unusually early September one happen with enough regularity here that most Zone 4 gardeners hold off on planting the most tender transplants until well after the average date has technically passed.

What Genuinely Thrives Here

A 125-140 day season comfortably fits most standard vegetable-garden crops without needing a specifically short-season variety, which is the main practical difference from Zone 3 just below it. Broccoli, cabbage, and kale (all in the 50-100 day range) mature reliably from a spring transplant, and full-season tomatoes and peppers - started indoors 6-8 weeks ahead - generally have enough runway to ripen a real harvest rather than finishing green at frost. Bush and pole beans both work well here, unlike in Zone 3 where pole beans' longer time to first harvest is a genuine liability.

Where the Margin Gets Thin

Winter squash and pumpkins on the longer end of their 80-120 day range (large pumpkin varieties especially) can still run close to the edge in a cool year, and sweet potatoes, at 90-120 days and needing consistent summer heat rather than just frost-free days, are a genuine stretch in the cooler parts of this zone - a Rocky Mountain Zone 4 valley and a Great Lakes Zone 4 location can differ meaningfully here even at the same zone number, since one gets more consistent summer heat than the other. Melons and watermelon similarly do better in the warmer pockets of this zone than the coolest ones.

A Working Planting Order

Onions, leeks, and celery go indoors first, in early-to-mid March, since none of the three can catch up if started later regardless of the zone.
Tomatoes, peppers, and eggplant follow indoors in late March to early April, giving them the standard 6-8 weeks before their mid-May move outside.
Peas, spinach, and radishes can go straight into the ground the moment it's workable - a light frost afterward won't set any of them back.
Broccoli, cabbage, and kale transplants move outdoors in early May, ahead of the window that opens later in the month for anything tender.
Once the soil has genuinely warmed by late May or early June, the tender crops go in: tomatoes, peppers, and basil transplanted, beans and squash direct-sown.

A Real Fall Garden Is Realistic Here

Unlike Zone 3, where the season barely accommodates a spring planting, Zone 4's roughly 130-day window leaves enough room for a genuine second planting: fast greens, radishes, and a second round of bush beans sown in mid-to-late July still have time to mature before the late-September or early-October frost. Counting backward from the average first frost date using each crop's specific days-to-maturity figure - rather than guessing - is the reliable way to know how late a fall sowing can go.

Season Extension

Row cover and cold frames are a genuine bonus rather than a requirement in Zone 4, mainly useful for pushing tender transplants out a week or two earlier than the average last frost date would otherwise allow, and for protecting a fall crop of hardy greens through the season's first light frosts to extend harvest well past the average first-frost date. This is a lower-stakes use of season-extension gear than in a shorter zone, where the same equipment can be the difference between a crop finishing or not.

A Good Zone for Perennial Crops to Establish

Asparagus and rhubarb, both slow to establish and needing a real winter dormancy to perform well long-term, do genuinely well across most of Zone 4 - the winters here are cold enough to satisfy their chill requirement reliably, and the growing season is long enough for a young crown to build real root reserves in its first couple of years before you start harvesting. This is a meaningful advantage over the very mildest zones, where garlic and other crops needing a real winter chill can struggle, and it's one of the reasons a Zone 4 garden planned around perennials as well as annuals tends to pay off over a multi-year horizon rather than just a single season.

Where Zone 4 Falls

Zone 4 covers a wide, climatically varied swath - the humid, lake-moderated summers of the upper Midwest and interior New England are a genuinely different growing environment from the drier, higher-elevation valleys of the Rockies and Intermountain West that also fall in this band, even though both share the same winter minimum temperature range. Summer humidity and rainfall affect disease pressure and irrigation planning more than the zone number alone reflects, so treat the zone as a frost-timing tool rather than a full description of your local climate.

Companion Planting Is the Same Across Zones

Everything on this page is about scheduling - when the frost window opens and closes, which crops fit inside it. It has no bearing on which crops actually pair well once they're both in your Zone 4 bed; for that half of the plan, the Companions section is the place to look.

Look up your frost dates →Build a planting calendar →

Frequently Asked Questions

What actually happens if I sow a fall crop a couple of weeks too late for Zone 4's frost date?

It depends on the crop's own cold tolerance, not just whether it technically reaches full size before frost. A frost-hardy crop like kale or spinach, caught immature by the first freeze, generally just pauses and keeps growing through a mild cold snap, finishing later than planned rather than dying. A frost-tender crop like bush beans sown too late simply gets killed outright at the first real frost with no partial-credit harvest - the more expensive mistake of the two, and worth planning around with a bit of built-in buffer.

Do sweet potatoes reliably mature in Zone 4?

It depends more on summer heat than on frost-free days alone - sweet potatoes need consistent warmth through the season, not just a long enough window on paper, so the warmer pockets of Zone 4 have a real edge over the coolest ones even at the same zone number.

Is a short-season tomato variety necessary in Zone 4?

Not usually, and the bigger practical benefit is timing flexibility rather than variety selection - waiting an extra week or two past the average last-frost date for genuinely warm soil, rather than transplanting the moment frost risk technically clears, costs far less relative benefit here than it would in Zone 3, where every day counts toward finishing before frost. That slack is often more useful to a first-time Zone 4 gardener than hunting for a faster variety.

Is Zone 4 cold enough for garlic and other crops that need winter chill?

Yes, comfortably. Fall-planted garlic goes through a genuine winter dormancy here and typically performs well the following summer - this is one of the zones where a real, sustained winter works in a grower's favor rather than being purely a constraint on the season length.