One of the best tools that you have as gardeners to help us estimate your gardening schedule is the 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.

One way of figuring out when to plant onions is to refer to the USDA zone info for Casper.

Planting Calendar for Onions

Frost tolerance for onions:	Very tolerant of frost.
When to plant:	Up to 7 weeks before last frost.

Onions do ok in cold weather which means that you can plant them quite a bit earlier in the year than more sensitive plants.

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

The last month that you can plant onions and expect a good harvest is probably September. Any later than that and your onions may not have a chance to really do well. Starting your onions indoors is a great way to get them started a few weeks earlier.

Last Frost Date

In Casper the average date of last frost happens on April 15. You should expect an average low temperature of -20°F in the coldest months of winter.

Keep in mind that the actual date of last frost is not always accurate because it is based on the USDA zone info for Casper and it is different every year. Half of the time in Casper last frost occurs after April 15 so be sure to be ready to cover your onions in the event of a late frost.

USDA Zone Info for Casper

Here is the info for USDA Zone 5a.

Average Date of Last Frost (spring)	April 15
Average Date of First Frost (fall)	October 15
Lowest Expected Low	-20°F
Highest Expected Low	-15°F

This means that on a really cold year, the coldest it will get is -20°F. On most years you should be prepared to experience lows near -15°F.

Plants to Grow in Casper

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