One of the best tools that you have as gardeners to help us determine 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.

The first opportunity to plant calendula in Zone 4a can be estimated by looking at the USDA zone info.

Planting Calendar for Calendula

Frost tolerance for calendula:	Tolerant of some frost.
When to plant:	Up to 5 weeks before last frost.

Since calendula do well in moderate cold you can plant them a little earlier in the year than other plants that might not handle the cold.

The earliest that you can plant calendula in Zone 4a 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 calendula and expect a good harvest is probably August. If you wait any later than that and your calendula may not have a chance to really do well. If you are starting your calendula indoors then you might be able to get away with starting them a little bit earlier.

Last Frost Date

In Zone 4a the average date of last frost happens on May 15. You should expect an average low temperature of -30°F in the coldest months of winter.

It's important to remember that USDA zone info for Zone 4a is an average and the actual date of last frost is different every year. Half of the time in Zone 4a last frost occurs after May 15 so make sure that you are prepared to protect your calendula in the event of a late frost.

USDA Zone Info for Zone 4a

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 Zone 4a

You may be interested in your other planting guides for Zone 4a.