Pennsylvania’s diverse geography means the optimal time to plant varies dramatically across the state. Establishing a successful garden requires pinpointing location-specific timing rather than relying on general guidelines. This guide provides specific planting windows tailored to Pennsylvania’s microclimates. This precision is necessary because a planting date that works in the mild southeast could mean a crop failure in the colder northern tier.
Understanding Pennsylvania’s Climate and Zones
Pennsylvania spans USDA Plant Hardiness Zones 5a (colder, higher elevations) to 7b (warmest, southeastern corners). This zoning system indicates the average annual minimum winter temperature, determining which plants survive winter outdoors. Hardiness zones are not the most precise tool for spring planting timing.
The more reliable metric is the average last frost date in spring and the average first frost date in fall. Last frost dates vary by over six weeks across Pennsylvania, occurring from mid-April near Philadelphia to mid-May or early June in northern regions. Gardeners must determine their local average to establish a safe baseline for planting tender crops.
Timing for Cool-Season Spring Crops
Cool-season crops thrive in early spring and can be planted before the danger of a hard freeze has passed, as they tolerate light frost. These hardy vegetables include peas, spinach, kale, radishes, and members of the cabbage family. The planting window typically opens in mid-March, four to six weeks before the average last frost date.
Soil temperature is a more accurate gauge than air temperature for these early plantings. Seeds for peas and spinach germinate when the soil reaches a minimum of 40°F, and transplants for broccoli and cabbage can be set out once the soil hits this threshold.
Direct sowing of root crops like carrots and beets should begin around late March to early April. Planting early allows these crops to mature before summer heat causes them to bolt, which degrades their flavor and texture.
Timing for Warm-Season Summer Crops
Warm-season crops are highly sensitive to frost and require both warm air and warm soil to flourish. These tender plants, which include tomatoes, peppers, eggplant, squash, and beans, must not be planted outdoors until after the average last frost date. This often means waiting until mid-May or early June in Pennsylvania.
The safest measure is waiting for the soil temperature to consistently reach 60°F at a depth of four inches before setting out transplants for peppers and eggplant. Tomatoes are slightly more tolerant and can be planted when the soil warms to 50°F. Seeds for these plants should be started indoors six to eight weeks before the target outdoor transplant date to develop robust seedlings.
Direct-sowing large-seeded vegetables like corn, bush beans, and cucumbers must also wait until the soil is reliably warm. This generally falls in the mid-May window for Zone 6 and late May to mid-June for colder Zone 5 areas. Prioritizing soil warmth over the calendar date ensures the best start, as planting into cold, wet soil can lead to poor germination and rot.
Extending the Season with Late and Fall Planting
The garden season extends beyond the summer harvest, allowing a second wave of planting in mid-summer for a fall yield. This practice, known as succession planting, focuses on replanting cool-season crops that perform well in the shorter, cooler days of autumn. Fall garden timing is calculated backward from the average first expected frost date, typically mid-October to early November.
To determine the correct date, consult the “days to maturity” on the seed packet and add a two-week buffer to account for reduced daylight and cooler temperatures. For example, a crop needing 60 days to mature should be planted 74 days before the first frost.
This mid-summer window, often July or early August, is suitable for restarting crops like kale, lettuce, spinach, and broccoli. Late fall is the correct time to plant crops intended to overwinter for a spring harvest, such as garlic and perennial onions, which are set into the ground in October or November before the soil freezes solid.