If you’re a Michigan gardener, knowing when to plant sweet potatoes is the key to a successful harvest. This guide will walk you through the optimal planting time and all the steps you need for a bountiful crop.
Sweet potatoes are a warm-season crop that love heat. Planting them at the right moment in Michigan’s sometimes unpredictable climate is crucial. Getting the timing wrong can lead to slow growth or even loss of your plants to cold soil.
When to Plant Sweet Potatoes in Michigan
The single most important factor is soil temperature. Sweet potatoes need warm soil to thrive and establish their roots quickly.
Understanding Your Michigan Planting Window
The optimal time to plant sweet potatoes in Michigan is from late May to mid-June. You should never rush to get them in the ground early. A late spring frost can be devastating.
Here’s how to pinpoint your best date:
- Target Soil Temperature: Wait until the soil is consistently at least 65°F (70°F is even better). Use a soil thermometer to check at a 4-inch depth in the morning.
- Frost Danger is Past: Plant 2-4 weeks after your area’s average last frost date. For southern Lower Michigan, this is often late May. For northern Michigan and the Upper Peninsula, aim for early to mid-June.
- Weather Watch: Watch the long-range forecast. A week of warm, sunny weather after planting is ideal for getting your slips established.
Preparing Your Sweet Potato Slips
You don’t plant seeds, you plant “slips,” which are small rooted sprouts. You can buy these online or from local nurseries, or grow your own from a sweet potato.
If you’re starting your own, begin about 6-8 weeks before your planned outdoor planting date. That means starting in mid-April for most Michigan gardeners.
- Take a healthy, organic sweet potato and suspend it in a jar of water (pointed end down).
- Place it in a warm, sunny window. Roots will from in the water, and slips will sprout from the top.
- Once slips are 6-8 inches tall with a few leaves, gently twist them off.
- Place these slips in their own shallow water to grow roots, which takes about a week.
Hardening Off Your Plants
This is a critical step! Your tender slips have been growing indoors. They need to slowly adjust to outdoor conditions like sun, wind, and cooler nights.
- Begin 7-10 days before planting.
- Place slips outside in a shaded, sheltered spot for a few hours each day.
- Gradually increase their time outside and exposure to direct sunlight.
- Bring them in at night if temperatures are forecasted to drop below 50°F.
Choosing and Preparing the Garden Site
Sweet potatoes demand loose, well-drained soil. They grow long roots, and heavy Michigan clay will stunt them.
- Sunlight: Choose the sunniest spot in your garden—at least 6-8 hours of direct sun daily.
- Soil: Amend clay soil with lots of compost or aged manure. Consider planting in raised beds or mounds, which warm up faster in spring and improve drainage.
- Fertilizer: Go easy on nitrogen. Too much leads to leafy vines and small tubers. Use a balanced or low-nitrogen fertilizer at planting, or mix in compost.
The Planting Process Step-by-Step
When your soil is warm and your slips are hardened, it’s time to plant.
- On planting day, water your slips thoroughly.
- Dig holes or a trench about 4-6 inches deep and 12-18 inches apart. Rows should be about 3 feet apart.
- Remove the lower leaves from each slip, leaving only the top few.
- Place the slip in the hole, burying the leafless stem right up to the remaining leaves. Roots will form all along the buried stem.
- Gently firm the soil around the plant.
- Water deeply after planting to settle the soil.
Using Black Plastic Mulch
This is a fantastic trick for Michigan gardeners. Covering your prepared bed with black plastic mulch 1-2 weeks before planting warms the soil significantly. It also suppresses weeds and retains moisture.
When it’s time to plant, simply cut an X in the plastic, dig your hole, and plant the slip through it. This method can give you a crucial head start.
Caring for Your Growing Sweet Potatoes
Once established, sweet potatoes are relatively low-maintenance.
- Watering: Water regularly for the first few weeks. Once established, they are drought-tolerant, but consistent moisture (about 1 inch per week) is best for good tuber development. Reduce watering in the last 3-4 weeks before harvest to help the potatoes cure.
- Weeding: Weed carefully early on. The vines will soon spread and shade out most weeds themselves.
- What Not to Do: Avoid heavy fertilizing during growth. Also, there’s no need to hill the soil around the plants like you do with regular potatoes.
When and How to Harvest in Michigan
Your sweet potatoes are ready to harvest in late September through October, but before the first hard frost. A light frost will damage the vines, but you should dig the tubers up immediately if a hard freeze is coming.
Signs of readiness include yellowing vines. Use a garden fork to carefully loosen the soil about 18 inches from the main plant to avoid spearing the tubers. Let them dry on the soil for a few hours.
Curing and Storage
This step is essential for sweetness and long storage. Michigan’s fall humidity is actually good for this.
- Gently brush off excess soil—do not wash them.
- Place them in a warm (80-85°F), humid place for 10-14 days. A small space with a heater and a pan of water can work.
- After curing, store them in a cool (55-60°F), dark, and well-ventilated place. Properly cured sweet potatoes can last for months.
FAQ: Sweet Potato Planting in Michigan
Can I plant sweet potatoes from the grocery store?
You can try, but it’s not always reliable. Store-bought potatoes are often treated with sprout inhibitors. For best results, buy certified disease-free slips or seed potatoes from a garden supplier.
What are the best sweet potato varieties for Michigan?
Choose short-season varieties that mature in around 90-110 days. Good options include ‘Beauregard’ (reliable, orange flesh), ‘Georgia Jet’ (fast-maturing, red skin), and ‘Covington’ (great flavor, disease resistant).
My leaves are being eaten. What’s wrong?
Several pests enjoy sweet potato vines, like flea beetles or sweet potato weevils (though the latter are rare in MI). Row covers early in the season can help. Mostly, the plants are vigorous and can handle some leaf damage without affecting the tuber yield.
Why did I get lots of vines but no big potatoes?
This usually points to three issues: planting too early in cold soil, too much nitrogen fertilizer, or not enough sunlight. Ensure you follow the soil temperature guide and choose a sunny spot.
With the right timing and a little preparation, growing sweet potatoes in Michigan is very rewarding. By waiting for warm soil in late spring and choosing a good site, you’ll be set for a fantastic fall harvest of homegrown sweetness.