Plant tomatoes in Pennsylvania after the last spring frost, which falls between mid-May and early June depending on your location in the state

Pennsylvania's frost dates divide the state into zones. The southern counties around Philadelphia and Pittsburgh have their last frost around mid-May; central Pennsylvania around State College reaches that date by late May; and the northern tier doesn't clear frost until early June. Tomatoes planted before the soil and air warm up will sit in cold ground and rot rather than grow. Waiting until after that frost date—and until nighttime temperatures stay above 50°F—gives seedlings the warmth they need to establish roots and begin growing.

You can also plant tomatoes in late summer for a fall harvest, typically starting in mid-July through early August. Fall tomatoes mature as temperatures drop, so they grow more slowly than spring plantings, but they often taste sweeter because the plant concentrates sugars as it ripens in cooler weather.

Key Takeaways

  • In southern Pennsylvania (Philadelphia, Pittsburgh areas), plant tomatoes after mid-May; in central Pennsylvania, wait until late May; in northern Pennsylvania, wait until early June.
  • Soil temperature should reach at least 60°F before planting, and nighttime air temperature should stay above 50°F consistently.
  • You can plant a second crop in mid-July through early August for a fall harvest that ripens as temperatures cool.
  • Starting seeds indoors 6 to 8 weeks before your planting date gives you larger transplants ready to go into the ground on time.

How to find your exact frost date in your Pennsylvania county

The National Weather Service publishes frost date maps by county. Search "National Weather Service frost dates Pennsylvania" and select your county to see the average date of the last spring frost and the first fall frost. These are historical averages, not guarantees—frost can arrive early or late in any given year—but they give you a reliable target window.

Your local Penn State Extension office also publishes frost dates for your area and can answer questions about your specific location. Extension offices are free and exist in every Pennsylvania county; you can find yours by searching "Penn State Extension [your county name]."

Soil temperature matters as much as air temperature

Tomato seeds and transplants need warm soil to germinate and grow. Soil temperature should reach at least 60°F, ideally 65°F or warmer. A soil thermometer (available at any garden center for under $10) tells you the actual temperature in your garden bed. Measure it in the morning in the spot where you plan to plant.

In Pennsylvania, soil typically reaches 60°F around the same time as the last frost date, but not always. A cold, wet spring can delay soil warming by a week or two. If you plant too early into cold soil, the roots sit dormant and the plant becomes stressed and vulnerable to disease. It is better to wait a week and plant into warm soil than to rush and lose the plant.

Starting seeds indoors gives you a head start

If you want larger plants ready to transplant on your planting date, start seeds indoors 6 to 8 weeks before. For mid-May planting in southern Pennsylvania, that means starting seeds in late March or early April. For early June planting in northern Pennsylvania, start seeds in mid-April.

Seedlings need bright light (a south-facing window or grow lights) and warmth (around 70°F) to grow stocky and strong. About a week before your planting date, move them outdoors for a few hours each day in a sheltered spot to harden them off—this acclimates them to outdoor sun and wind so they don't wilt when planted.

Hardening off transplants prevents transplant shock

Whether you grew seedlings yourself or bought transplants from a nursery, they need a gradual transition to outdoor conditions. Start by placing them outside in shade for 2 to 3 hours on a mild day. Each day, increase the time outdoors and gradually move them into more sun. After 7 to 10 days, they can stay outside overnight if temperatures stay above 50°F.

Hardening off takes time but prevents the wilting and leaf damage that happens when a tender plant suddenly faces full sun and wind. Skipping this step often kills transplants or stunts their growth for weeks.

Fall planting extends your harvest into autumn

Plant a second crop of tomatoes in mid-July through early August for harvest in September and October. Fall tomatoes grow more slowly because daylight hours are shrinking and temperatures are dropping, but they often develop deeper flavor because the plant ripens fruit in cooler weather.

Choose determinate (bush) varieties for fall planting rather than indeterminate (vining) types, because bush tomatoes mature faster and will finish before the first frost. Check the seed packet or plant label for "days to maturity"—look for varieties that mature in 60 to 75 days. The first fall frost in Pennsylvania typically arrives between mid-October (southern counties) and late September (northern counties), so you need varieties that can finish before then.

Protect young plants from late spring frost if weather turns cold

Even after you plant, a surprise frost can arrive. If the forecast calls for frost within a week of planting, cover plants with a frost cloth, row cover, or even old bed sheets draped over stakes. Leave the cover on until the temperature rises above freezing the next morning, then remove it so the plant gets sunlight.

Established plants that have been in the ground for several weeks are more resilient than newly planted seedlings. A single frost night usually won't kill a plant that has had time to develop roots, but young transplants can be killed by even a light frost.

Frequently Asked Questions

Can I plant tomatoes in early May in Pennsylvania?

In southern Pennsylvania, early May is too early—soil is usually still cold and frost risk is high. In central and northern Pennsylvania, it is definitely too early. Wait until soil reaches 60°F and nighttime temperatures stay above 50°F. Planting too early results in stunted growth or root rot, not an earlier harvest.

What if I plant tomatoes and then frost comes?

Cover plants with frost cloth or sheets if frost is forecast within a week of planting. If plants are already in the ground and frost arrives, water them thoroughly the morning after—this helps them recover. Established plants usually survive a light frost, but newly planted seedlings may be killed.

Do I need to start seeds indoors, or can I direct-seed tomatoes in the garden?

Tomato seeds need warm soil and a long growing season. Direct seeding in the garden usually results in plants that are too small to produce fruit before the first fall frost. Starting seeds indoors 6 to 8 weeks early gives you mature plants that can flower and set fruit on schedule.

What is the difference between spring and fall tomato planting?

Spring tomatoes have the whole warm season to grow and produce. Fall tomatoes mature as temperatures cool, so they grow more slowly but often taste sweeter. Fall crops must finish before the first frost, so choose fast-maturing varieties (60 to 75 days) and plant by early August at the latest.

How do I know if my soil is warm enough?

Use a soil thermometer pushed 4 inches into the ground in the morning. Tomatoes need soil at least 60°F, ideally 65°F or warmer. In Pennsylvania, this usually coincides with the last frost date, but a cold, wet spring can delay soil warming by a week or two.