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.

It's a good idea to figure out when it's the best time to plant zinnia by looking at the USDA zone info for Castle Rock.

Planting Calendar for Zinnia

Frost tolerance for zinnia:	Not tolerant of frost.
When to plant:	After all chance of frost has passed.

It's probably not a good idea to plant zinnia until after the last frost when the weather gets warmer because they are not cold tolerant.

The earliest that you can plant zinnia in Castle Rock is April. However, you really should wait until May if you don't want to take any chances.

The last month that you can plant zinnia and expect a good harvest is probably August. You probably don't want to wait any later than that or else your zinnia may not have a chance to grow to maturity. You can get started a couple of weeks earlier by starting your zinnia indoors.

Last Frost Date

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

Always keep in mind that USDA zone info for Castle Rock is not always accurate and the actual date of last frost is different every year. Half of the time in Castle Rock you get surprised by a frost after April 15 so make sure that you are ready to cover your zinnia if you have a surprise late frost.

USDA Zone Info for Castle Rock

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 Castle Rock

You may be interested in your other planting guides for Castle Rock.