The USDA Zone info is a great tool for gardeners to help us estimate your gardening schedule. The zone info helps tell us things like average date of last frost and lowest expected temperature for your area.

You will be able to figure out when to plant tree onions by using the USDA zone info for Helena.

Planting Calendar for Tree onions

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

You can plant tree onions just a tiny bit earlier in the year because they do ok in moderate cold.

The earliest that you can plant tree onions in Helena 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 tree onions and expect a good harvest is probably August. You probably don't want to wait any later than that or else your tree onions may not have a chance to really do well. You can get started a little bit earlier by starting your tree onions indoors.

Last Frost Date

In Helena 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 Helena is not always accurate the actual date of last frost is different every year. Half of the time in Helena there is a last frost after March 15 so make sure that you are prepared to cover your tree onions if you have a late frost.

USDA Zone Info for Helena

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 Helena

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