Before planting it is a good idea to find your USDA Zone info to figure out your garden schedule. The most important data that the zone info tells us is average last frost and the lowest expected temperature for your area.

One way of determining when it's a good idea to plant zinnia is to check out the USDA zone info for Philadelphia.

Planting Calendar for Zinnia

Frost tolerance for zinnia:	Not tolerant of frost.
When to plant:	After all chance of frost has passed.

You can not plant zinnia until after the last frost because they require warm weather.

The earliest that you can plant zinnia in Philadelphia is April. However, you really should wait until May if you don't want to take any chances.

The last month that you can plant zinnia and expect a good harvest is probably August. You probably don't want to wait any later than that or else your zinnia may not have a chance to really do well. You can get started a couple of weeks earlier by starting your zinnia indoors.

Last Frost Date

On average the last frost when the weather gets warmer is on April 15 in Philadelphia. You should expect an average low temperature of 0°F in the coldest months of winter.

Remember that USDA zone info for Philadelphia is not always accurate and the actual date of last frost changes from year to year. Since half of the time in Philadelphia you get surprised by a frost after April 15 be ready to protect your zinnia if you have a late frost.

USDA Zone Info for Philadelphia

Here is the info for USDA Zone 7a.

Average Date of Last Frost (spring)	April 15
Average Date of First Frost (fall)	October 15
Lowest Expected Low	0°F
Highest Expected Low	5°F

This means that on a really cold year, the coldest it will get is 0°F. On most years you should be prepared to experience lows near 5°F.

Plants to Grow in Philadelphia

You may be interested in your other planting guides for Philadelphia.