Before planting it is a good idea to find your USDA Zone info to estimate your garden 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 Denver should be used to determine when it's possible to plant helianthemum.

Planting Calendar for Helianthemum

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

Helianthemum can survive in mild cold which tells us that you can plant them just a bit earlier in the year than plants that are more sensitive to the cold.

The earliest that you can plant helianthemum in Denver 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 helianthemum and expect a good harvest is probably September. You probably don't want to wait any later than that or else your helianthemum may not have a chance to fully mature. Starting your helianthemum indoors is a great way to get them started a couple of weeks earlier.

Last Frost Date

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

Just be sure to remember that USDA zone info for Denver is an average and the actual date of last frost is different every year. Since half of the time in Denver last frost occurs after April 15 be ready to cover your helianthemum if you have a late frost.

USDA Zone Info for Denver

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 Denver

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