Before planting it is a good idea to find your USDA Zone info to figure out 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 possible to estimate when you can plant ageratum by referring to the USDA zone info for Johnston.

Planting Calendar for Ageratum

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

Ageratum are not cold tolerant which tells us that it is important to wait until it warms up after the last frost has passed before you can plant them.

The earliest that you can plant ageratum in Johnston 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 fully mature. Starting your ageratum indoors is a great way to get them started a few weeks earlier.

Last Frost Date

The average date of last frost is April 15 in Johnston. It might get as low as -20°F during the coldest months of winter.

It's important to remember that the actual date of last frost may not be accurate from year to year because it is based on the USDA zone info for Johnston and it is different every year. Half of the time in Johnston it frosts late in the year after April 15 so make sure that you are prepared to cover your ageratum in the event of a surprise late frost.

USDA Zone Info for Johnston

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 Johnston

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