When To Plant Sweet Potatoes In Pa

If you’re a gardener in Pennsylvania, knowing when to plant sweet potatoes is the key to a successful harvest. This guide will walk you through the optimal planting season and all the steps you need for a bountiful crop.

Sweet potatoes are a warm-season crop that love heat and hate frost. Getting the timing right in Pennsylvania’s varied climate is crucial. Planting too early can lead to rot in cold soil, while planting too late shortens the growing season.

The single most important factor for planting sweet potatoes is soil temperature. Your goal is warm soil and no threat of frost.

The Golden Rule: Soil Temperature & Frost Dates

You must wait until the soil is consistently at least 60°F (65°F is even better). This usually happens 2-4 weeks after your last spring frost date. You can use a simple soil thermometer to check.

Last Frost Dates in PA: These vary widely. In southeastern PA (Philadelphia area), the average last frost is around April 15-25. In central PA (State College), it’s May 1-10. In northwestern PA (Erie), it can be as late as May 15-25.
Optimal Planting Window: For most of Pennsylvania, the safe, optimal planting time for sweet potato slips is late May through mid-June. In warmer southeastern areas, you might plant in mid-May. In cooler northern zones, early June is safer.

Understanding Your Growing Zone

Pennsylvania spans USDA Hardiness Zones 5b to 7a. Your zone helps refine your timing.

Zone 6 & 7 (Southeastern PA, parts of South Central): You have a longer season. Aim for mid to late May, after soil warms.
Zone 5 & 6 (Most of Central, Northern, & Western PA): Be more patient. Early to mid-June is often the best bet to ensure warm enough conditions.

Preparing for Planting: Slips vs. Seeds

Sweet potatoes are grown from “slips,” which are small rooted sprouts. You rarely grow them from seeds. You have two options:

Buy Slips: Order from a reputable nursery. They’ll ship them at the correct time for your area.
Grow Your Own Slips: Start a sweet potato in water or soil about 6-8 weeks before your planned planting date. This gives you full control.

How to Harden Off Your Slips

If your slips were grown indoors or mailed to you, they need to adjust to outdoor life. This process is called hardening off.

Start 7-10 days before planting.
Place slips outside in a shaded, protected spot for a few hours each day.
Gradually increase their time outside and exposure to sunlight.
Bring them in at night if temperatures drop below 50°F.

Step-by-Step Planting Guide

Once your soil is warm and slips are hardened, you’re ready to plant.

Choose a Sunny Site: Pick the sunniest spot in your garden—at least 6-8 hours of direct sun daily.
Prepare the Soil: Sweet potatoes prefer loose, well-drained, slightly sandy soil. Heavy clay soil can be ammended with compost. They like a slightly acidic pH (5.8-6.2). Avoid high-nitrogen fertilizers, which promote leaves, not roots.
Create Mounds or Rows: Form raised mounds or ridges about 8-10 inches high. This improves drainage and soil warmth. Space mounds 12-18 inches apart in rows 3 feet apart.
Plant the Slips: Plant slips deeply, burying the stem up to the first set of leaves. This encourages more root development along the stem. Water them in well.
Mulch Heavily: After planting, apply a thick layer of black plastic mulch or straw. Black plastic is excellent for PA as it warms the soil further and suppresses weeds.

Caring for Your Sweet Potato Plants

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 1 inch of water per week. Reduce watering in the last 3-4 weeks before harvest to improve flavor.
Weeding: Be careful when weeding, as roots are shallow and spreading. Mulch heavily to minimize weeds.
No Heavy Fertilizing: If needed, use a low-nitrogen, potassium-rich fertilizer (like a 5-10-10 blend) early in the season.
Vine Management: The vines will sprawl everywhere. You can gently redirect them if needed, but avoid turning or lifting them, as this can damage the roots.

When and How to Harvest in PA

Your harvest time depends on your planting date. Sweet potatoes need 90-120 frost-free days to mature.

Timing: Harvest before the first fall frost. Frost damages the roots and leaves. In PA, this is typically late September through October. You’ll know they’re ready when the leaves start to yellow.
Method: Use a garden fork to carefully loosen the soil several inches away from the main stem. Lift the cluster of roots gently to avoid bruising.
Curing is Critical: This step is non-negotiable for good flavor and storage. Brush off excess soil (don’t wash). Cure them in a warm (80-85°F), humid place (about 85% humidity) for 10-14 days. A small space heater and humidifier in a bathroom or basement corner can work.
Storage: After curing, store your sweet potatoes in a cool (55-60°F), dark, and well-ventilated place. Properly cured and stored, they can last for months.

Common Challenges in Pennsylvania

Being prepared for these issues will help you succeed.

Cool, Wet Springs: This is the biggest hurdle. Be patient and wait for warm soil. Using black plastic mulch is a huge help.
Short Growing Season: In cooler zones, choose faster-maturing varieties like ‘Georgia Jet’ or ‘Beauregard’.
Pests: Watch for voles, deer, and flea beetles. Row covers can protect young plants.
Diseases: Rot is caused by cold, wet soil. Proper planting timing and good drainage prevent most issues.

Recommended Varieties for PA Gardens

Choosing a variety suited to a shorter, cooler season is smart.

Beauregard: Reliable, fast-maturing, with good yields. A great all-around choice.
Georgia Jet: Known for its fast growth, making it excellent for northern areas like PA.
Covington: Similar to Beauregard, with a consistent shape and good disease resistance.
O’Henry: A white-fleshed variety with a creamy texture that performs well in various conditions.

FAQ: Sweet Potato Planting in Pennsylvania

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 from a garden center.

What’s the latest I can plant sweet potatoes in Pennsylvania?

To ensure enough growing days, try to get slips in the ground by late June. Early July plantings are risky unless you use a very fast-maturing variety and have a long fall forecast.

Can I grow sweet potatoes in containers?

Yes! Use a large container (20-gallon fabric pots work well) with excellent drainage. Fill with a light, sandy potting mix. This is a great option if your garden soil is heavy clay.

Why are my sweet potato leaves turning yellow?

Late in the season, it’s a sign of maturity. If it happens early, it could be overwatering, a nutrient deficiency, or a disease. Check your soil moisture first.

By following this guide and paying close attention to soil temperature, you can enjoy a successful harvest of homegrown sweet potatoes. The wait for warm soil is worth it for those sweet, homegrown roots in the fall.