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

The USDA zone info for Thief River Falls can be looked at to estimate when you can plant primula.

Planting Calendar for Primula

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

Primula tend to make it in cold weather which tells us that you can plant them quite a bit earlier in the year than other plants that might not handle the cold.

The earliest that you can plant primula in Thief River Falls 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 primula and expect a good harvest is probably August. If you wait any later than that and your primula may not have a chance to fully mature. You can get started a little bit earlier by starting your primula indoors.

Last Frost Date

On average the last frost when the weather gets warmer is on May 15 in Thief River Falls. It might get as low as -35°F during the coldest months of winter.

Since the USDA zone info for Thief River Falls is not always accurate the actual date of last frost can change quite a bit from year to year. Half of the time in Thief River Falls it frosts late in the year after May 15 so make sure that you are prepared to cover your primula if you have one of those late frosts.

USDA Zone Info for Thief River Falls

Here is the info for USDA Zone 3b.

Average Date of Last Frost (spring)	May 15
Average Date of First Frost (fall)	September 15
Lowest Expected Low	-35°F
Highest Expected Low	-30°F

This means that on a really cold year, the coldest it will get is -35°F. On most years you should be prepared to experience lows near -30°F.

Plants to Grow in Thief River Falls

You may be interested in your other planting guides for Thief River Falls.