One of the best tools that you have as gardeners to help us figure out your gardening schedule is the USDA zone info. The zone info helps tell us things like average date of last frost and lowest expected temperature for your area.

In Sterling you can estimate when it's a good idea to plant primula by reviewing the USDA zone info.

Planting Calendar for Primula

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

Primula are one of those plants that can tolerate quite a bit of cold weather which tells us that you can get them planted much earlier than other plants that might not handle the cold.

The earliest that you can plant primula in Sterling 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 fully mature. You can get started a couple of weeks earlier by starting your primula indoors.

Last Frost Date

The average date of last frost is April 15 in Sterling. You can expect an average low temperature of -20°F in the coldest months of winter.

It's important to remember that the actual date of last frost is an average because it is based on the USDA zone info for Sterling and it will vary from year to year. Half of the time in Sterling you get surprised by a frost after April 15 so make sure that you are prepared to cover your primula in the event of one of those late frosts.

USDA Zone Info for Sterling

Here is the info for USDA Zone 5a.

Average Date of Last Frost (spring)	April 15
Average Date of First Frost (fall)	October 15
Lowest Expected Low	-20°F
Highest Expected Low	-15°F

This means that on a really cold year, the coldest it will get is -20°F. On most years you should be prepared to experience lows near -15°F.

Plants to Grow in Sterling

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