One of the first steps you take when you are estimating your gardening schedule is find your USDA Zone info. 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 Thornton should be used to estimate when it's possible to plant hollyhocks.

Planting Calendar for Hollyhocks

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

Since hollyhocks are moderately cold tolerant you can plant them a little bit earlier in the year than other plants that might not handle the cold.

The earliest that you can plant hollyhocks 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 hollyhocks and expect a good harvest is probably September. Any later than that and your hollyhocks may not have a chance to really do well. If you are starting your hollyhocks indoors then you might be able to get away with starting them a couple of weeks earlier.

Last Frost Date

On average all chance of frost has passed is on April 15 in Thornton. In the coldest months of winter you can expect an average low temperature of -15°F.

Keep in mind that USDA zone info for Thornton is just an average and the actual date of last frost can change quite a bit from year to year. Half of the time in Thornton you get surprised by a frost after April 15 so be sure to be ready to cover your hollyhocks 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.