Michigan · zones 4b–6b
When to plant sweet potatoes in Michigan.
Sow or transplant between Jun 11 to Jul 26 in a typical year, keyed to Michigan's median last frost around May 5. Dates below are state medians; your ZIP code shifts them by days to weeks.
Season checkSweet Potato needs about 110 days and your first frost comes too early for that. Even the earliest date shown will not ripen outdoors here, grow it in a container you can move, or treat it as a short-season variety.
The 2026 windows
Sweet Potatoes dates for a typical Michigan season.
1 · Start indoors
Apr 30 to Jun 14
About 6 weeks before set-out. Warm spot, real light.
2 · Set out
Jun 11 to Jul 26
Keyed to the ~May 5 last frost. Sow 3" deep, 14" apart.
Harvest
~110 days later
~2.5 lb per plant over ~1 weeks.
Michigan spans more than one climate: Zone 6 is the most common zone, but the state runs 4b to 6b. That's why the planner works from your ZIP code's frost dates, not your zone: mountain and coastal gardens in the same state can be three weeks apart.
Michigan growing notes
A hundred and ten days is Michigan's tightest sweet potato math.
Banking heat before the clock runs out
Sweet potato is grown from a rooted slip, not seed, so there is no germination line to hit; the plant simply sulks in cold dirt and takes off once the ground has caught up to it. Wait until frost danger has fully passed and the soil holds around 65 degrees before slips go in. Michigan's statewide season of around 156 frost-free days leaves little room to spare once that slow start is factored in against a crop needing 110 days to finish, and with only a spring planting window and no fall option to fall back on if the first round stalls, getting slips into genuinely warm ground on the first try matters more for this crop than for almost anything else grown here.
Black plastic mulch laid over ridged rows a week or two before setting slips is close to standard practice this far north for exactly that reason: it runs the top several inches of soil noticeably warmer than bare ground and holds that heat into the evening, which speeds the slips rooting in and keeps vines growing through cooler stretches later in the season that would otherwise stall them.
Digging before frost matters more than digging on schedule
Sweet potato roots are damaged by exposure to temperatures near freezing even before the vines themselves show frost injury, so waiting for a visible frost to signal harvest time risks chilling injury to the roots still underground, injury that will not show up until well into storage as soft, sunken spots. Watching the forecast and digging ahead of a predicted frost, rather than reacting to one that has already happened, protects a crop that took the whole season to grow.
Curing right after digging is what turns a fresh, starchy root into the sweet, storable one people expect: 85 degrees with the air held at 90 to 95 percent relative humidity for a run of about 4 to 7 days heals over any digging wounds and converts a share of the root's starch to sugar, after which the crop stores best around 55 to 60 degrees. A Michigan gardener without a dedicated curing space can improvise one in a warm closet with a humidifier or a covered tub with a damp towel, and this is the one step growers skip most often, which is exactly why so many homegrown sweet potatoes disappoint at the table months later.
Deer, not Colorado potato beetle, are the vine you have to watch
Colorado potato beetle does plenty of damage a few rows over in a true potato bed, but it cannot touch a sweet potato vine. The beetle only completes its life cycle on nightshade leaves, potato, tomato, pepper, eggplant, and sweet potato belongs to the morning glory family instead, a plant the beetle has no use for at any stage. A gardener who spots the black-and-cream striped adult in the garden should look at the potato hills for where it is actually feeding, not the sweet potato ridge.
Deer are the animal actually worth fencing this crop against here, since the broad leaves draw them in and one overnight visit near a wood's edge can strip a young planting back to bare vine before the roots underneath have sized up. Check the row each morning once vines start spreading, looking for ragged, torn leaf edges rather than the clean cut a rabbit leaves; two mornings of fresh browsing inside a single week is worth stringing a temporary fence line around the bed. Michigan's short slip season already leaves this crop little room to recover a setback, so protecting the leaf canopy matters more here than it would on a crop with a longer runway left to regrow.
In Michigan: watch for
The pests that find sweet potatoes here.
A middle-length season, about 156 frost-free days, means sweet potato overlaps wireworms & white grubs for a stretch each summer. Check plants every week or two and treat early.
Wireworms & white grubs
Shallow holes and grooves chewed into the roots, found only at digging time.
Organic fix: Avoid planting into ground that was in sod last year; rotate away from grassy beds.
Clusters on the tender growing tips of new vines.
Organic fix: Hose them off in the morning, or use insecticidal soap.
Black rot
Dry, firm dark patches on the roots, usually found at harvest or in storage, with a sweet fruity smell.
Organic fix: Start from clean slips cut well above the soil line, never save roots from a bad crop, and rotate 3 years.
Your season math: Michigan gives sweet potatoes about 156 frost-free days, and it needs roughly 110 days to a first harvest. It's a one-planting crop, so time that single sowing well.
Planting sweet potatoes in Michigan: questions
When should I plant sweet potatoes in Michigan?+
In a typical Michigan year, sow sweet potatoes or set out transplants between Jun 11 to Jul 26, keyed to the state's median last frost around May 5. Your exact dates shift with your ZIP code and microclimate.
When do I start sweet potatoes seeds indoors in Michigan?+
Start seeds inside about 6 weeks before set-out: roughly Apr 30 to Jun 14 for a typical Michigan season.
What USDA zone is Michigan?+
Michigan spans zones 4b–6b, mostly zone 6. But frost dates, not zones, set planting time. The free planner uses your ZIP code's actual frost dates.
How many sweet potatoes plants do I need?+
Depends who you're feeding. The crop page has exact counts per household size, or the free planner does the math for your family in about 60 seconds.