One of the best tools that you have as gardeners to help us estimate 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.

By reviewing the USDA zone info for Spearfish you should be able to estimate when you can plant ageratum.

Planting Calendar for Ageratum

Frost tolerance for ageratum:	Not tolerant of frost.
When to plant:	After the last frost.

Since ageratum require warm weather you have to wait until after the last frost when the weather gets warmer before you can plant them.

The earliest that you can plant ageratum in Spearfish 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 ageratum and expect a good harvest is probably August. You probably don't want to wait any later than that or else your ageratum may not have a chance to really do well. You can get started a little bit earlier by starting your ageratum indoors.

Last Frost Date

On average the last frost when the weather gets warmer is on April 15 in Spearfish. In the coldest months of winter you should expect an average low temperature of -20°F.

Keep in mind that USDA zone info for Spearfish is not always accurate and the actual date of last frost can change quite a bit from year to year. Since half of the time in Spearfish last frost occurs after April 15 be ready to cover your ageratum if you have a late frost.

USDA Zone Info for Spearfish

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 Spearfish

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