Now that Indianapolis has finally had temperatures below 30 degrees F, you might be wondering what will become of your annuals. Many will die with the cold. Tender annuals cannot tolerate frost at all and decline as the weather cools. This includes impatiens, marigolds, flowering tobacco, zinnias, petunias, coleus, and begonias.
Some annuals look good up until frost. These are termed half-hardy annuals. They are killed by frost but their attractive late into fall. They probably look better in fall than they did in the middle of the summer. Half-hardy annuals include cleome, forget-me-nots, mealycup sage, strawflower, and love-in-mist. Half-hardy annuals can be planted outdoors in spring about the time the crabapples finish blooming.
Hardy annuals can tolerate a light frost. Sweet allysum, bachelor’s button (cornflower), annual larkspur, and pot marigold (Calendula) fall into this group. Sweet allysum at White River Gardens is still looking good and much better than it did in the heat of the summer. This is an unusual group of plants. You can plant the seed for these outdoors in fall and tiny plants will overwinter to bloom early in spring, then deteriorate in summer. You can also put out plants in spring when it is still quite cool, about the time Forsythia bloom.
In researching this group of plants, it’s clear there is some disagreement about which plants fall in which category. I used an article from North Carolina State University as my guide - http://www.ces.ncsu.edu/depts/hort/consumer/factsheets/annuals/text/types.html.
