One of the first steps you take when you are getting a good idea your gardening schedule is find your USDA Zone info. The most important data that the zone info tells us is average last frost and the lowest expected temperature for your area.

In Hermiston you can determine when it's the best time to plant cosmos by checking out the USDA zone info.

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 can survive in some cold which tells us that you can plant them just a tiny bit earlier in the year than other plants that might not handle the cold.

The earliest that you can plant cosmos in Hermiston 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 fully mature. If you are starting your cosmos indoors then you might be able to get away with starting them a couple of weeks earlier.

Last Frost Date

In Hermiston the average date of last frost happens on April 15. In the coldest months of winter you should expect an average low temperature of 0°F.

Keep in mind that the actual date of last frost may not be accurate from year to year because it is based on the USDA zone info for Hermiston and it changes from year to year. Half of the time in Hermiston there is a last frost after April 15 so always be ready to protect your cosmos in the event of one of those late frosts.

USDA Zone Info for Hermiston

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 Hermiston

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