Before planting it is a good idea to find your USDA Zone info to determine 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.

In Iron Mountain you can determine when to plant onions by reviewing the USDA zone info.

Planting Calendar for Onions

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

Since onions do well in cold you can plant them much earlier in the year than more sensitive plants.

The earliest that you can plant onions in Iron Mountain 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 onions and expect a good harvest is probably August. You probably don't want to wait any later than that or else your onions may not have a chance to really do well. If you are starting your onions indoors then you might be able to get away with starting them a few weeks earlier.

Last Frost Date

In Iron Mountain the average date of last frost happens on May 15. You can expect an average low temperature of -30°F in the coldest months of winter.

Since the USDA zone info for Iron Mountain is an average the actual date of last frost is different every year. Half of the time in Iron Mountain you get a frost after May 15 so always be ready to cover your onions if you have one of those late frosts.

USDA Zone Info for Iron Mountain

Here is the info for USDA Zone 4a.

Average Date of Last Frost (spring)	May 15
Average Date of First Frost (fall)	September 15
Lowest Expected Low	-30°F
Highest Expected Low	-25°F

This means that on a really cold year, the coldest it will get is -30°F. On most years you should be prepared to experience lows near -25°F.

Plants to Grow in Iron Mountain

You may be interested in your other planting guides for Iron Mountain.