When To Plant Potatoes In Zone 7b

Knowing when to plant potatoes in zone 7b is the first step to a succesful harvest. Getting the timing right protects your seed potatoes from late frosts and gives them a long, productive growing season.

This guide gives you the specific dates and soil conditions to aim for. We’ll also cover how to choose the right varieties and care for your plants all the way to harvest.

For most of zone 7b, the optimal planting window is from late February through mid-March. The goal is to get potatoes into the ground 2-4 weeks before your last average spring frost date.

You can use your last frost date as a benchmark. If your area’s last frost is around April 15th, target planting between March 15th and April 1st. Soil temperature is a more reliable guide than the calendar alone.

Key Signs Your Soil is Ready

Potatoes need cool, but not frozen, soil to begin growing. Planting in cold, soggy soil can cause seed pieces to rot instead of sprout.

Soil Temperature: Aim for a consistent 45°F (7°C) at a 4-inch depth. Use a soil thermometer for accuracy.
Soil Texture: The soil should be dry enough to crumble in your hand, not clump into a muddy ball. If its too wet, wait a week.
Frost Forecast: While potatoes can handle a light frost after foliage emerges, a hard freeze will damage them. Be prepared to cover new sprouts if a severe cold snap is predicted.

Two-Planting Strategy for Extended Harvest

You’re not limited to just one planting. Many gardeners in zone 7b use a succesive planting method.

Early Spring Planting: Plant your main crop in March. These will be your classic summer harvest potatoes.
Late Summer Planting: Plant a second crop in late July or early August. These are for a fall harvest of tender new potatoes, or a full harvest if you have a long, mild autumn.

Choosing Potato Varieties for Your Season

Potatoes are categorized by how many days they need to mature. This affects your planting and harvest timing.

Early Season (70-90 days): Like ‘Red Norland’ or ‘Yukon Gold’. Great for early harvests and for the late-summer planting window.
Mid-Season (90-110 days): Like ‘Kennebec’ or ‘Purple Majesty’. Reliable main-crop choices for the spring planting.
Late Season (110-135 days): Like ‘Russet Burbank’. Need the full, frost-free season from an early spring planting.

Step-by-Step Planting Guide

Follow these steps to ensure your seed potatoes get the best possible start.

1. Sourcing and Preparing Seed Potatoes

Always use certified disease-free seed potatoes from a garden center or reputable online seller. Grocery store potatoes are often treated to prevent sprouting.

Chitting (Pre-sprouting): Place seed potatoes in a bright, cool (50-60°F) spot for 2-4 weeks before planting. This encourages strong, stubby sprouts.
Cutting: A day before planting, cut larger seed potatoes into pieces. Each piece should be about the size of a golf ball and have at least 2-3 “eyes” (sprout buds).
Curing: Let the cut pieces sit out overnight so the cut surfaces dry and form a callus. This prevents rot when planted.

2. Planting Your Potatoes

Site Selection: Choose a spot with full sun (at least 6 hours) and well-drained soil. Potatoes grown in heavy, wet clay are more prone to disease.
Soil Prep: Loosen the soil deeply. Mix in 2-4 inches of compost or well-rotted manure. Avoid fresh manure or high-nitrogen fertilizers, which promote leafy growth instead of tubers.
Trench Method: Dig a trench 6-8 inches deep. Place seed pieces cut-side down, 12 inches apart, in the trench. Space rows 2-3 feet apart.
Covering: Gently cover the seed pieces with 4 inches of soil. Do not pack it down tightly. Water the area well after planting.

Caring for Your Potato Plants

Proper care after planting is simple but crucial for a good yield.

Hilling: The Most Important Task

Hilling protects developing tubers from sunlight, which turns them green and toxic. It also encourages the plant to produce more potatoes along the buried stem.

When green shoots reach about 6-8 inches tall, use a hoe to mound soil around the base, leaving just the top few leaves exposed.
Repeat this process every few weeks until the plants begin to flower. By then, the hill should be about 6-12 inches high.

Watering and Feeding

Potatoes need consistent moisture, especially once tubers start forming (around flowering time).

Provide 1-2 inches of water per week. Inconsistent watering leads to knobby or cracked potatoes.
Water at the soil level, not overhead, to keep foliage dry and prevent disease.
Side-dress with a balanced, low-nitrogen fertilizer or compost when you begin hilling.

Pest and Disease Watch

Stay vigilant for common issues in zone 7b’s humid climate.

Colorado Potato Beetle: Hand-pick the yellow-and-black striped adults and red larvae. Check leaf undersides for orange egg clusters.
Early/Late Blight: Fungal diseases that cause dark leaf spots. Ensure good air flow, water at the base, and remove affected plants. Rotate your potato crop location each year.
Flea Beetles: These create tiny shot-holes in leaves. Use row covers when plants are young.

Harvesting and Storage

Knowing when and how to harvest ensures your potatoes store well.

When to Harvest

New Potatoes: For tender, thin-skinned potatoes, harvest a few tubers from the side of the hill about 2-3 weeks after plants stop flowering. These do not store long.
Mature Potatoes (for storage): Wait until the plant’s foliage has completely yellowed and died back. This allows the skins to toughen up for long-term storage.

How to Harvest

Use a digging fork on a dry day, inserting it well away from the plant’s center to avoid spearing tubers.
Gently lift the plant and sift through the soil with your hands to find all the potatoes.
Let potatoes cure on the soil surface for 2-3 hours to dry, but don’t let them sit in direct sun for longer, as they can sunscald.

Curing and Storing

For your main storage crop, proper curing is essential.

Brush off excess soil—do not wash them.
Place undamaged potatoes in a single layer in a dark, well-ventilated place with high humidity (about 85-95%) and cool temperatures (50-60°F) for 10-14 days. This helps skins harden and minor nicks to heal.
After curing, store potatoes in complete darkness in a cool (38-40°F), humid place, like a basement or root cellar. Use breathable bags or boxes. Check them periodically and remove any that are spoiling.

Frequently Asked Questions (FAQ)

Can I plant potatoes in the fall in zone 7b?

Yes, a fall planting in late summer is possible. Plant around early August for a late fall harvest. You’ll need to use early-season varieties to ensure they mature before a hard freeze.

What happens if I plant potatoes too early?

Planting in soil that is too cold and wet can cause seed pieces to decay before they sprout. Its better to wait for the soil to warm slightly than to rush.

How do I protect potato plants from a late frost?

If a frost is forecast after your plants have emerged, cover them with row fabric, old blankets, or even a thick layer of loose straw. Remove the coverings once the temperature rises above freezing.

Can I grow potatoes in containers in this zone?

Absolutely. Container growing is a great option. Use a large pot or grow bag, ensure excellent drainage, and follow the same planting and hilling principles, using a quality potting mix.

Why are my potato leaves turning yellow?

Yellowing leaves late in the season is normal as the plant matures. Yellowing early on can signal overwatering, nutrient deficiency, or the onset of disease like early blight. Check your watering habits and inspect for other symptoms.

Following this guide for when to plant potatoes in zone 7b sets you up for a rewarding harvest. By paying attention to soil temperature, choosing suitable varieties, and providing consistent care with hilling and watering, you can enjoy homegrown potatoes from your summer and fall garden. Remember, a little patience at the start of the season pays off with baskets full of fresh potatoes later on.