Milwaukee’s soil, not the date on your kitchen calendar, decides when tomatoes and peppers go in the ground here. Warm-season transplants want soil that’s genuinely warmed through, and that typically doesn’t happen until after the last spring freeze window closes near the end of April, with the season running until the first fall freeze settles in around mid-to-late October. Before anything else, buy a soil thermometer and start checking the bed where those transplants are headed, because that reading is the one number that tells you whether this is the week to plant or the week to wait. If you’re itching to get started earlier, there’s still plenty of cold-hardy work to do while you wait; see What to Plant in Wisconsin in January, What to Plant in Wisconsin in February and What to Plant in Wisconsin in March. For what to get started as that late-April window arrives, see What to Plant in Wisconsin in April, and for a fuller rundown of what to get in the ground once that window opens, see What to Plant in Wisconsin in May. For what can still go in as June arrives, see What to Plant in Wisconsin in June, and once the heat of summer settles in, see What to Plant in Wisconsin in July for what still has time to go in the ground. And as the season winds down, see What to Plant in Wisconsin in August for what still has time to go in, and What to Plant in Wisconsin in September for what can still be planted before that first fall freeze arrives.
The frost window in Wisconsin
Two dates define the Wisconsin gardening year: the last spring freeze and the first fall freeze. At Milwaukee, NOAA’s NCEI 1991-2020 climate normals put the last spring frost (32°F) between April 16 and April 29, and the first fall frost between October 17 and October 29. Those are 30-70% freeze-probability windows, not single days, so treat them as the range in which a freeze becomes likely rather than a date you can circle on a calendar.
What the range means for your growing season
Do the arithmetic and Milwaukee’s growing season runs from about 171 days, if you land on the late end of spring and the early end of fall, to roughly 196 days, if you get the earliest possible last frost and the latest possible first frost. Most years fall somewhere in between. That’s a wide enough spread that a gardener who waits for the state average to pass can still get caught by a late freeze, and one who plants at the earliest date in the range can gain several extra weeks of harvest in a mild year, right up until it’s time to start winding the garden down; see What to Plant in Wisconsin in October for the tail end of that stretch and What to Plant in Wisconsin in November for what comes after.
These figures come from a station near Lake Michigan, and the lake itself changes the picture. Lake Michigan holds its summer heat into fall and delays the first freeze right along the shoreline, while inland stretches of southern Wisconsin typically see their first freeze in early October, well ahead of the shoreline; once the garden is fully put to bed, see What to Plant in Wisconsin in December for what little there is left to do before winter fully sets in. lakefront. Head north and the season compresses further, with the first freeze arriving earlier still. A gardener in the far north of the state should treat Milwaukee’s dates as a rough southern benchmark, not a working schedule.
Gardeners in other short-season states run the same math with different inputs. Connecticut’s planting calendar deals with a comparably tight spring-to-fall window shaped by its own coastal and inland split, which is worth a look if you want to see how a different state handles the same problem.
A season of five to six-and-a-half months sounds generous, but frost-tender crops need to finish before the first fall freeze, and many need to go in well after the last spring frost because soil, not air, has to warm first. That leaves less room than the raw day count suggests, which is why the crop sections below work backward from these two dates rather than from a fixed calendar month.
Cool-season crops
Peas, spinach, lettuce, brassica transplants, and root crops all tolerate light frost, which is why they go in the ground well before Milwaukee’s last spring frost of April 16 to April 29, per NOAA’s normals, rather than after it. These crops germinate in cold soil and their leaves or roots shrug off a dip into the high 20s, so waiting for frost-free weather just wastes weeks of a short season.
Timing by crop
Direct-sow peas, spinach, and leaf lettuce four to six weeks ahead of the last frost date. Counting back from Milwaukee’s window, six weeks before April 16 lands in early March, and four weeks before April 29 lands in early April, so the practical sowing stretch runs from early March to early April depending on how quickly your soil dries out and warms enough to work. Wet, cold clay soil in early spring can rot pea seed before it sprouts, so wait for the soil to crumble rather than smear when you squeeze it.
Brassica transplants, broccoli, cabbage, and their relatives, go out two to four weeks before last frost, which works out to roughly mid-March through mid-April at Milwaukee. Start the transplants indoors five to six weeks before that outdoor date so they’re a sturdy few inches tall and hardened off, not leggy, by the time they go in the ground.
Root crops split into two groups. Radishes and turnips can go in as early as the peas, since they germinate in cold soil and mature fast enough to dodge most problems. Carrots and beets do better sown a couple of weeks later, once the soil has warmed slightly, because cold soil slows their germination to a crawl and lets weeds get ahead of the row.
- Peas, spinach, leaf lettuce: direct sow, cold-tolerant seed
- Broccoli, cabbage, kale: transplant as hardened seedlings
- Radishes, turnips: earliest root crops, fast maturity
- Carrots, beets: sow slightly later once soil has warmed
A hard freeze well below freezing can still damage even these tolerant crops, so keep row cover on hand for a cold snap in late March or early April, especially the first year you push the early end of these windows.
Warm-season crops
Tomatoes, peppers, squash, beans, and corn are frost-tender at every stage, and soil temperature governs them more than the calendar does. Cold soil rots bean and squash seed before it germinates and stalls tomato roots even if the transplant survives above ground. Waiting a week or two past the last frost date for the soil to actually warm almost always outperforms planting on the calendar date alone.
Tomatoes: matching variety to margin
Catalogue days-to-maturity figures are counted from transplant, not from seed, and they shift by a week or so depending on the season, so use them as a guide rather than a guarantee. Working from Milwaukee’s frost window, all of the varieties below get set out late April to mid May, once the last-frost window has passed and soil has had time to warm.
| Variety | Days to maturity | Type | Margin before frost |
|---|---|---|---|
| Sakura | 55 | Indeterminate | 102 days |
| Edox | 55 | Indeterminate | 102 days |
| Valentine | 55 | Indeterminate | 102 days |
| Glacier | 55 | Determinate | 102 days |
| Sun Gold | 57 | Indeterminate | 100 days |
| Supersweet 100 | 60 | Indeterminate | 97 days |
| Juliet | 60 | Indeterminate | 97 days |
| Amalfi | 68 | Determinate | 89 days |
| Cherokee Purple | 72 | Indeterminate | 85 days |
| Big Beef Plus | 72 | Indeterminate | 85 days |
| Tiren | 75 | Indeterminate | 82 days |
| Granadero | 75 | Indeterminate | 82 days |
| San Marzano II | 78 | Indeterminate | 79 days |
| Celebrity Plus | 78 | Determinate | 79 days |
The early group, Sakura, Edox, Valentine, and Glacier, all carry over 100 days of margin before frost, which is enough buffer to survive a delayed transplant or a run of cool weather without losing the harvest. The 78-day varieties, San Marzano II and Celebrity Plus, run closer to 79 days of margin, tight enough that a cold, wet spring pushing transplanting back by two weeks eats into that buffer noticeably. Disease resistance is worth weighing alongside days to maturity in Wisconsin’s humid summers: Sakura, Edox, and Valentine all resist Fusarium Wilt races 1 and 2, Big Beef Plus and Celebrity Plus resist Gray Leaf Spot, and Amalfi carries intermediate resistance to both early and late blight.
Getting transplants ready
To hit a late-April to mid-May transplant date, start tomato and pepper seed indoors six to eight weeks earlier. Counting back from that transplant window puts indoor sowing at roughly late February through late March, with the earlier end of that range suiting gardeners aiming for the earlier end of the transplant window. Peppers size up more slowly outdoors than tomatoes, so give them, if anything, the later end of the sowing range rather than the earlier one.
Beans, squash, and corn are direct-seeded, not transplanted, and should wait until soil has warmed and the frost date has firmly passed, typically a week or two after the last-frost window closes, since their seed rots quickly in cold, wet ground rather than sitting dormant until conditions improve.
The fall planting window
Fall crops get planted by working backward from the first freeze instead of forward from the last one. Milwaukee’s first fall frost falls between October 17 and October 29, per NOAA’s 1991-2020 normals, and the earlier date, October 17, is the safer one to plan around if you garden away from the lake’s moderating effect.
Counting back from frost
Take the days-to-maturity figure on the seed packet, add 10 to 14 days to account for the slower growth and shorter daylight of late summer and early fall, and count back from October 17. A crop that needs 40 days to mature, for example, needs roughly 54 days of growing time worked backward from that date, landing the sowing date in late August. A 60-day crop needs about 74 days, pushing the sowing date into early August. It’s the same arithmetic used for the spring transplant dates above, just run in the opposite direction.
Fast-maturing crops fit this window comfortably: spinach, leaf lettuce, radishes, and turnips can all be sown in mid to late summer for a fall harvest. Slower crops like storage carrots or full-size cabbage need to go in earlier, often close to the peak of summer heat, which means starting them in soil that’s too warm for ideal germination unless you shade the row or water it in well.
Some crops actually improve after a light frost. Kale, Brussels sprouts, parsnips, and spinach convert starch to sugar when temperatures drop, and plenty of Wisconsin gardeners deliberately leave these in the ground past the first light freeze for a sweeter harvest. A hard freeze, not a light one, is what ends the season for good, so don’t rush to pull frost-tolerant crops the moment the thermometer dips.
Tomatoes, peppers, beans, and squash have no such second act. Once a fall frost is forecast, pick everything that’s ripe or close to it, since a single hard freeze ends their production outright regardless of how much of the season is technically left. Row cover or a cold frame can push the harvest window later for the frost-tolerant crops, buying another week or two beyond that first light freeze without much added cost or effort. Louisiana gardeners work with a dramatically longer fall window, as our Louisiana planting calendar lays out, since frost arrives so much later in the Gulf South.
Reading a planting calendar properly
A state-wide planting calendar, including the dates in this one, is built from a single weather station and averaged over thirty years. It is a starting point, not an instruction, and treating it as an exact schedule is the most common mistake new Wisconsin gardeners make.
What actually shifts the dates
Elevation matters: a garden on a ridge or in the state’s higher northern counties sits in colder air than a lakeside plot at the same latitude. Lake effect matters too, and it cuts both ways. Lake Michigan delays the first fall freeze along the shoreline but can also produce cool, damp spring air that keeps soil temperatures down longer than a few miles inland. Urban heat from pavement and buildings can push a city garden’s effective frost dates a few days earlier in fall and later in spring than the surrounding countryside, and a low-lying spot that collects cold air overnight can freeze on a night when a garden a quarter mile away does not.
The 30-70% probability band NOAA uses for these dates also means exactly what it says: even at the safest end of the window, there’s still a real chance of a freeze. A late cold snap after the average last-frost date has passed is not rare, and it happens often enough that experienced Wisconsin gardeners keep frost cloth on hand well into May.
The fix is to watch your own garden rather than the calendar alone. Keep a cheap soil thermometer and check it before transplanting warm-season crops. Note which corners of your yard frost first and last over a couple of seasons, and you’ll build a more accurate personal calendar than any state-wide figure can give you.
Local help
Frost dates and soil conditions vary by county across Wisconsin, and the Wisconsin Extension service publishes county-level planting guidance and offers a soil test that a state-wide calendar can’t replace. Actual nutrient levels and pH in your own plot matter more to yield than shaving a few days off a planting date. For anyone building out a broader garden plan for the state, our Wisconsin guides cover the rest of the state’s growing conditions in more detail.
Common questions
Does the Milwaukee frost date apply to my town too?
Not exactly. These figures come from one NOAA weather station near Milwaukee, and towns north, inland, or at higher elevation than that station will see later spring frosts and earlier fall frosts, sometimes by weeks rather than days. Use the Milwaukee dates as a reference point and adjust based on how your area compares, or check with the Wisconsin Extension service for county-level guidance.
I already put my tomatoes out and a frost is forecast. What do I do?
Cover them before nightfall with a bedsheet, row cover, or overturned buckets, making sure the material reaches the ground to trap soil heat. A light frost near 32°F can still kill unprotected tomato and pepper foliage even though the plant itself might survive at the roots, so don’t assume a mild-sounding forecast is harmless to exposed leaves.
How do I know if my soil is warm enough for beans and squash?
Push a soil thermometer a couple of inches into the row and check it in the morning, since soil holds the previous day’s cold overnight. Bean and squash seed sits and rots in cold, wet soil rather than germinating, so a short delay after the last frost date is often cheaper than a failed first planting that has to be reseeded anyway.
Can I get a second harvest of lettuce or spinach in the same season?
Yes, sow a second round in mid to late summer for a fall harvest, timed by counting back from the first fall frost rather than planting on a fixed date. Lettuce and spinach both bolt in the heat of a Wisconsin summer, so a mid-season sowing often does better in partial shade or with the row started once the worst of the heat has started to ease.
What’s the real difference between a light frost and a hard freeze?
A light frost sits right around 32°F and damages tender leaf tissue without necessarily killing the whole plant, while a hard freeze drops well into the 20s and kills roots and stems outright. The NOAA frost dates in this calendar mark the light-frost threshold, which is why frost-tolerant crops like kale and carrots can keep growing for weeks after that date has technically passed.
Related guides
- Michigan Planting Calendar: When to Sow and Plant, Frost Dates Included
- Minnesota Planting Calendar: When to Sow and Plant, Frost Dates Included
- Connecticut Planting Calendar: When to Sow and Plant, Frost Dates Included