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.

By checking out the USDA zone info for Thornton you will be able to determine when it's possible to plant primula.

Planting Calendar for Primula

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

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

The earliest that you can plant primula in Thornton 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 primula and expect a good harvest is probably September. Any later than that and your primula may not have a chance to really do well. You can get started a few weeks earlier by starting your primula indoors.

Last Frost Date

The average date of last frost is April 15 in Thornton. It might get as low as -15°F during the coldest months of winter.

Just be sure to remember that the actual date of last frost is an average because it is based on the USDA zone info for Thornton and it will vary from year to year. Half of the time in Thornton you get surprised by a frost after April 15 so just be sure to be ready to protect your primula if you have one of those late frosts.

USDA Zone Info for Thornton

Here is the info for USDA Zone 5b.

Average Date of Last Frost (spring)	April 15
Average Date of First Frost (fall)	October 15
Lowest Expected Low	-15°F
Highest Expected Low	-10°F

This means that on a really cold year, the coldest it will get is -15°F. On most years you should be prepared to experience lows near -10°F.

Plants to Grow in Thornton

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