When To Plant Sweet Potatoes In Zone 8b

If you’re gardening in zone 8b, knowing when to plant sweet potatoes is the key to a big harvest. This guide will walk you through the optimal planting season and all the steps you need for success.

Getting the timing right is everything. Sweet potatoes are a warm-season crop that love heat and hate cold soil. Planting at the correct time ensures your plants have a long, warm growing season to produce those tasty tubers.

Understanding Your Zone 8b Climate

Zone 8b has mild winters and long, hot summers. The average minimum winter temperature is between 15 to 20°F. Your last spring frost typically falls in late March or early April. The first fall frost usually arrives in mid to late November.

This gives you a very long growing season of over 200 days. That’s perfect for sweet potatoes, which need 90 to 120 frost-free days to mature. The long season allows for a great harvest even if you get a slightly later start.

The Optimal Planting Window

The best time to plant sweet potatoes in zone 8b is from mid-April through mid-June. You should not plant them until the soil is thoroughly warm.

Early to Mid-April: This is often the earliest safe date, but only if the soil temperature has reached at least 65°F. Use a soil thermometer to check. Cold soil will stunt the plants.
May to Early June: This is the prime planting window. The soil is reliably warm, and air temperatures are consistant. Plants established now will grow vigorously.
Mid-June: This is your last call for planting. Slips planted by mid-June will still have enough time to produce a decent harvest before the first fall frost.

A good rule of thumb is to plant your slips about 2 to 4 weeks after your last average frost date. Waiting for warm soil is more important than the calendar date.

How to Check Soil Temperature Correctly

Don’t guess—measure. Soil temperature is the most reliable indicator for planting.

Buy an inexpensive soil thermometer from a garden center.
Check the temperature at a depth of 4 inches in the morning, when the soil is at its coolest.
Take readings for several days in a row. The soil should be consistently at 65°F or higher before you plant.

If you don’t have a thermometer, a folk method is to sit on the bare soil. If it feels comfortably warm (not cool) to your skin, it’s probably ready.

What Happens if You Plant Too Early?

Planting in cold soil is the most common mistake. Sweet potato slips are very sensitive to chill. If the soil is below 60°F, the plants will just sit there and not grow. They become vulnerable to rot and disease. You’ll lose valuable growing time and may end up with weak plants that produce little.

Preparing Your Garden Bed

Sweet potatoes thrive in loose, well-drained soil. They don’t need rich soil, but they do need room for their roots to expand easily.

Location: Choose the sunniest spot in your garden. They need full sun—at least 6 to 8 hours of direct sunlight daily.
Soil Type: Sandy loam is ideal. If you have heavy clay soil, you must amend it. Raised beds or mounded rows work exceptionally well in zone 8b to improve drainage and warm the soil faster.
Soil pH: Aim for a slightly acidic pH of 5.8 to 6.2. You can get a simple test kit to check your levels.
Fertilizer: Go easy on nitrogen. Too much nitrogen gives you huge vines but small tubers. Use a balanced or low-nitrogen fertilizer at planting, or mix in compost.

Prepare your beds a week or two before planting. Turn the soil and remove any rocks or hard clumps that could misshape the potatoes.

Choosing and Planting Your Slips

You grow sweet potatoes from “slips,” which are small rooted sprouts. You can buy them online or from local nurseries, or grow your own from a store-bought sweet potato.

Acclimate Your Slips: If your slips arrive in the mail or have been indoors, harden them off for a week. Set them outside in a shady, protected spot for a few hours each day, gradually increasing their sun exposure.
Planting Depth and Spacing: Plant slips deep to encourage good root development. Bury them up to the bottom leaves. Space slips 12 to 18 inches apart in rows that are 3 to 4 feet apart.
Watering In: Water the slips thoroughly right after planting to settle the soil around the roots.

Some gardeners prefer to lay black plastic mulch over the bed before planting. This warms the soil even more, suppresses weeds, and conserves moisture. Just cut holes to plant the slips through.

Caring for Your Growing Sweet Potatoes

Sweet potatoes are relatively low-maintenance once established.

Watering: Water regularly for the first few weeks. Once established, they are drought-tolerant but produce best with consistent moisture. Water deeply once a week if there’s no rain. Reduce watering in the last 3-4 weeks before harvest to help the tubers cure and develop their sweetness.
Weeding: Weed carefully early on. Once the vines spread and cover the ground, they will shade out most weeds.
No Heavy Fertilizing: Avoid adding more nitrogen fertilizer during the growing season. A side dressing of potash (potassium) in mid-summer can be beneficial for tuber development.
Pest Control: Watch for deer, rabbits, and voles. Insect pests are usually minimal, but keep an eye out for sweet potato weevils (a serious pest in the South). Rotate your crop each year to help prevent disease.

The Harvest Timeline in Zone 8b

Your planting date determines your harvest date. Most varieties need 90 to 120 days from planting to harvest.

If you planted in mid-April, you can start checking for harvest in mid-August.
A May planting leads to a September harvest.
A June planting will be ready in October.

You must harvest before your first fall frost. Frost will damage the vines and can harm the tubers in the ground. If frost is forecasted, harvest immediately.

Signs Your Sweet Potatoes Are Ready

The tubers are ready when they are a usable size. You can actually harvest a few early as “new” potatoes if you want. For your main harvest, look for these signs:

The leaves and vines start to yellow slightly.
The days to maturity for your variety have passed.
Cooler fall weather has arrived.

To check, gently dig around the base of a plant with your fingers to feel the size of a tuber or two. If they look a good size, it’s time.

Step-by-Step Harvest and Curing

Use a digging fork, not a shovel, to carefully loosen the soil about 18 inches away from the main stem.
Lift the plant and gently shake off the soil. Handle the tubers carefully, as their skin is very thin and easily bruised at harvest.
Brush off excess soil; do not wash them.
Sort them, discarding any that are cut or badly damaged.
Curing: This critical step heals wounds and converts starches to sugars. Place undamaged tubers in a warm (80-85°F), humid place for 10 to 14 days. A shaded porch or a warm room works.
After curing, store them in a cool (55-60°F), dark, and well-ventilated place. Properly cured and stored sweet potatoes can last for many months.

FAQ: Sweet Potatoes in Zone 8b

Can I plant sweet potatoes in July in zone 8b?

It’s not recommended. Planting in July gives the tubers too little time to develop before fall coolness arrives. You might get a few small potatoes, but the yield will be disappointing.

What are the best sweet potato varieties for my zone?

Zone 8b can grow almost any variety well. Popular choices include Beauregard (reliable, fast-maturing), Georgia Jet (good for heavier soils), and Covington (great flavor and storage). For something different, try a white or purple variety.

Can I grow sweet potatoes in containers?

Yes! Use a large container (at least 20 gallons) with excellent drainage. Fill it with a light, sandy potting mix. This is a great option if your garden soil is heavy clay.

How do I save my own slips for next year?

Save a few healthy, medium-sized tubers from your harvest. In late winter (February/March), place them in a jar with water or half-buried in moist potting soil in a warm spot. They will sprout slips that you can twist off and root in water once they have leaves.

Why did my plants grow lots of vines but no potatoes?

This is usually caused by too much nitrogen fertilizer, planting too early in cold soil, or getting a late start that didn’t allow enough growing days. Also, overwatering late in the season can sometimes cause this issue.

By following this guide and hitting that optimal planting window from mid-April to mid-June, you’ll set your sweet potato crop up for maximum success. Paying attention to soil warmth, providing loose soil and full sun, and giving them time to cure after harvest will reward you with a plentiful, homegrown supply to enjoy all winter long.