When To Plant Sweet Potatoes In Zone 7b

If you’re gardening in zone 7b, 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 bounty of homegrown tubers.

Sweet potatoes are a warm-season crop that love heat. Planting them at the right moment ensures they have a long enough growing season to produce those tasty roots. Getting the timing wrong can lead to disappointing results.

For zone 7b, the optimal time to plant sweet potato slips is in late spring, after all danger of frost has passed and the soil has thoroughly warmed. This typically falls between mid-May and early June.

You must wait until both the air and soil are consistently warm. Sweet potatoes are extremely sensitive to cold. Planting too early into cool soil can stunt their growth or even kill the young slips.

Why Soil Temperature is Crucial

The soil temperature is more important than the calendar date. Your goal is to have soil that is at least 60°F (15.5°C) at a depth of 4 inches. For ideal growth, aim for 65–70°F (18–21°C).

You can use a simple soil thermometer to check. If you don’t have one, a good rule of thumb is to wait until about 2-4 weeks after your last average spring frost date. For many in zone 7b, the last frost is around mid-April.

Using Your Last Frost Date as a Guide

Find your exact last frost date through local extension services. Once you have that date, count forward 3 to 4 weeks. This is your target planting window. Rushing to plant in early May can often backfire if you have a late cold snap.

Preparing for the Planting Window

Don’t wait until May to get ready. Your preparation should begin much earlier. Here’s a timeline to follow:

January–February: Order your sweet potato slips or start your own from organic sweet potatoes.
March–April: Prepare your garden bed. Choose a sunny spot and amend the soil.
Late April–Early May: Harden off your home-started slips if you have them ready.
Mid-May to Early June: Plant your slips when conditions are perfect.

What Are Sweet Potato Slips?

Slips are the small rooted sprouts that grow from a sweet potato. You don’t plant the potato itself in the garden. Instead, you plant these slips, which become the new plants. You can buy them from reputable nurseries or grow your own.

How to Start Your Own Slips

Starting slips is easy and rewarding. Here’s how:

Take a healthy, organic sweet potato (store-bought ones are sometimes treated to prevent sprouting).
Suspend it in a jar of water using toothpicks, so the bottom half is submerged.
Place the jar in a warm, bright windowsill.
In a few weeks, sprouts (slips) will emerge from the top. When they 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.
Once roots are well-formed, they are ready for hardening off and planting.

Choosing the Right Variety for Zone 7b

Selecting a variety with a good days-to-maturity that fits your season is important. Look for varieties that mature in 90-120 days. Some excellent choices for zone 7b include:

Beauregard: The most common, reliable, and fast-maturing (90 days).
Georgia Jet: Known for its quick maturity (90 days) and good yields in shorter seasons.
Centennial: Another reliable, orange-fleshed variety.
O’Henry: A white-fleshed, creamy variety with good yield.

Step-by-Step Planting Guide

When your soil is warm and slips are ready, follow these steps:

Soil Preparation: Sweet potatoes prefer loose, well-draining, slightly sandy soil. Work in several inches of compost to improve texture and fertility. They prefer a slightly acidic pH of 5.8-6.2.
Creating Mounds or Rows: Form raised mounds or ridges about 8-10 inches high. This improves drainage and warms the soil faster, which is a big benefit in zone 7b.
Planting the Slips: Space your slips 12-18 inches apart in the row, with rows 3-4 feet apart. Plant them deep, burying the entire stem up to the first set of leaves. New roots will form along the buried stem.
Watering In: Water thoroughly immediately after planting to settle the soil around the roots.

Caring for Your Sweet Potato Plants

Sweet potatoes are relatively low-maintenance once established.

Watering: Water consistently for the first few weeks. Once established, they are drought-tolerant but produce best with 1 inch of water per week. Reduce watering in the last 3-4 weeks before harvest to prevent splitting.
Weeding: Weed carefully when plants are young. The vines will quickly spread and shade out most weeds on their own.
Fertilizing: Go easy on nitrogen! Too much nitrogen leads to huge vines and tiny tubers. Use a balanced or low-nitrogen fertilizer at planting, if needed.
Do Not Prune: Let the vines run. They are not like regular potatoes; the vines are where the plant stores energy for the roots.

When to Harvest in Zone 7b

Your harvest time will be in late September through October. The most important sign is to harvest before your first fall frost. Frost will damage the vines and can harm the tubers in the ground.

Look for yellowing leaves as a natural sign of maturity. Gently dig a test hill to check tuber size. Use a garden fork, starting far from the main stem to avoid spearing your crop.

Curing and Storing Your Harvest

This step is non-negotiable for good storage. Sweet potatoes need to be cured to heal wounds and convert starches to sugars.

Brush off excess soil gently; do not wash them.
Place them in a warm (80-85°F), humid place for 10-14 days. A greenhouse, sunny porch, or near a heater can work.
After curing, store them in a cool (55-60°F), dark, and well-ventilated place. Properly cured sweet potatoes from zone 7b can last for many months.

Common Problems and Solutions in Zone 7b

Being prepared for pests helps. The main pest is the sweet potato weevil (less common in cooler zones) and voles. Rotate your crop each year to prevent soil-borne diseases. Deer may browse the vines; fencing is the best deterrent if they become a problem.

FAQ: Sweet Potatoes in Zone 7b

Can I plant sweet potatoes in July in zone 7b?

Planting in July is generally too late. The tubers won’t have enough warm days to size up properly before fall frosts arrive. Stick to the late spring window.

What if I have a late frost after planting my slips?

Be prepared to cover your young plants with frost cloth or row covers if an unexpected late frost is forcasted. Having some protection on hand is a smart precaution.

Can I grow sweet potatoes in containers in zone 7b?

Absolutely! Use a large container (20-gallon or bigger) with excellent drainage. This is a great option if your garden soil is heavy clay. Just remember container soil heats up and cools faster.

How do I know my soil is warm enough without a thermometer?

A traditional method is to sit bare-bottomed on the soil—if it’s comfortably warm to the skin, it’s likely ready. A less humorous method is to wait until nighttime temperatures are consistantly above 55°F.

Should I use black plastic mulch?

Black plastic mulch is highly recommended in zone 7b. It warms the soil significantly earlier in the season, suppresses weeds, and conserves moisture. It can let you plant a week or two earlier, which is a valuable advantage.

By following this guide and paying close attention to soil temperature, you can master the timing for planting sweet potatoes in zone 7b. With proper care, you’ll be rewarded with a generous harvest of homegrown sweet potatoes to enjoy all winter long.