It can be a challenge to find good information about what plants need and when it’s safe to plant them outside. This printable table provides sunlight and soil depth requirements, along with the earliest dates to start or transplant these vegetables and berries outside. This information applies to gardens in the Philadelphia metro area, which is USDA hardiness zone 7. The soil depth requirements also assume you are growing varieties that are suitable to container growing.
You can start plants anytime after the dates shown. If you choose to start early, make sure you watch the weather, and gently cover your plants if it gets “cold” again. For annual vegetable plants, “cold” generally means mid-thirties or lower. You could also watch weather forecasts for frost or freeze warnings. It’s also important to remember that the conditions that damage tender plants are determined not only by air temperature, but also by soil temperature, moisture, wind, and precipitation.
Determining the “last frost date” is not an exact science. Current estimates of the last frost date for Philadelphia range from April 6 through April 30. At EFTE, we have scheduled seed starting according to a last frost between April 15 and April 22.
If you are a relatively new gardener, it’s safer to err on the side of caution, and plant your garden later rather than sooner. If your plants are in the ground too soon, they might survive the conditions, but they won’t be as productive as they would otherwise.