The USDA Zone info is a great tool for gardeners to help us estimate your gardening schedule. The most important data that the zone info tells us is average last frost and the lowest expected temperature for your area.

In Alton you can determine when it's possible to plant catharanthus by reviewing the USDA zone info.

Planting Calendar for Catharanthus

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

It's probably not a good idea to plant catharanthus until after the last frost when the weather gets warmer because they require warm weather.

The earliest that you can plant catharanthus in Alton 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 catharanthus and expect a good harvest is probably August. Any later than that and your catharanthus may not have a chance to fully mature. You can get started a few weeks earlier by starting your catharanthus indoors.

Last Frost Date

On average the last frost has passed is on April 15 in Alton. It might get as low as -10°F during the coldest months of winter.

Since the USDA zone info for Alton may not be accurate from year to year the actual date of last frost changes from year to year. Half of the time in Alton last frost occurs after April 15 so make sure that you are prepared to protect your catharanthus if you have one of those late frosts.

USDA Zone Info for Alton

Here is the info for USDA Zone 6a.

Average Date of Last Frost (spring)	April 15
Average Date of First Frost (fall)	October 15
Lowest Expected Low	-10°F
Highest Expected Low	-5°F

This means that on a really cold year, the coldest it will get is -10°F. On most years you should be prepared to experience lows near -5°F.

Plants to Grow in Alton

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