Tomatoes are popular in home gardens for a variety of reasons: they are versatile, productive and easy to grow. Pennsylvania's climate varies from one part of the state to another, and demands that tomatoes be planted at the right time if they are to thrive.
Temperature is the most important factor determining when you plant tomatoes outdoors. Sub-freezing temperatures can kill young tomato plants, and hard frosts can occur well into spring in Pennsylvania. Hold off on planting tomatoes until the soil temperature is at least 60 degrees and all danger of frost is well behind you.
Dates of last frost vary across the state. In the warmest, southeastern corner of Pennsylvania, nights are generally frost-free by late April. But high-altitude areas of northwestern Pennsylvania can see frost as late as June 30. Consult Penn State's Freeze Date map to decide when it is safe to plant tomatoes in your backyard.
Tomato plants are ready to be planted in the garden when they are 6 to 8 inches tall. You can buy seedlings from a nursery, or you can grow them yourself from seed. If you choose to grow from seed, plant them in containers indoors about eight weeks before you plan to transplant.