One of the first steps you take when you are making a decision about your gardening schedule is find your USDA Zone info. The zone info helps tell us things like average date of last frost and lowest expected temperature for your area.

A way of getting a good idea when it's the best time to plant cosmos is to look at the USDA zone info for Riverdale.

Planting Calendar for Cosmos

Frost tolerance for cosmos:	Tolerant of a very small amount of frost.
When to plant:	Up to 3 weeks before last frost.

Cosmos are one of those plants that can tolerate a tiny bit of cold weather which means that you can start planting them slightly earlier than plants that are more sensitive to the cold.

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

The last month that you can plant cosmos and expect a good harvest is probably August. Any later than that and your cosmos may not have a chance to grow to maturity. If you are starting your cosmos indoors then you might be able to get away with starting them a few weeks earlier.

Last Frost Date

In Riverdale the average date of last frost happens on March 15. In the coldest months of winter you should expect an average low temperature of 10°F.

Since the USDA zone info for Riverdale is an average the actual date of last frost will vary from year to year. Since half of the time in Riverdale you get surprised by a frost after March 15 be ready to protect your cosmos in the event of a late frost.

USDA Zone Info for Riverdale

Here is the info for USDA Zone 8a.

Average Date of Last Frost (spring)	March 15
Average Date of First Frost (fall)	November 15
Lowest Expected Low	10°F
Highest Expected Low	15°F

This means that on a really cold year, the coldest it will get is 10°F. On most years you should be prepared to experience lows near 15°F.

Plants to Grow in Riverdale

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