Gardening with Galligan: Asters and other autumn perennials

CAROL GALLIGAN PHOTO | A very nice aster, Woods Light Blue, blooming in half shade.

Years ago, the genus Aster contained more than 600 species. In the 1990s, however, the North American species began to be treated separately. After this division, there remained roughly 180 species within the genus, most of which were confined to Eurasia. But those available in the United States are more than welcome this time of year when most of our perennials are either fading fast or have already gone to seed.

Asters are relatively easy to grow, prefer full sun but will manage with part sun, and are not fussy about soil or its pH. Some bloom in the summer, but most wait until fall. They come in a range of colors, although there is still not a yellow one. They are mostly shades of pink and purple, a light blue and white. They range in height from 8 inches to very tall and have many uses, both in borders as well as wildflower gardens.

Asters can be grown from seed, but germination is described in the literature as “uneven.” This suggests that buying plants is probably preferable. But if you do want to try germination, refrigerate your seed for at least six weeks before starting them in flats. A better alternative is to take shoots from already existing plants in spring, choosing those that look strong and vigorous to ensure your chances for success.

Because asters prefer climates with cool, moist summers and what we have here on Shelter Island is hot, moist summers, using a good thick mulch, at least 2 inches deep, is advisable. Depending on the type, they should be planted at least 1 foot apart and perhaps more.

You can encourage “bushiness” by pinching, which will also increase your bloom. Depending on the species, they will most likely need to be staked. Like other perennials, they probably should be divided every few years to keep the plant vigorous and the flower quality good.

Asters are not disease-free; they are susceptible to most of the fungi that occur in our humid summers, including powdery mildew, rusts, mites and aphids. If your asters acquire any of these, proceed in the usual fashion, spraying with an antifungal mixture.

Among the varieties available, my favorite is Purple Dome. If you come across it anywhere for sale, don’t hesitate; its flowers are a lovely shade of dark purple, and although I have it planted in a far from ideal position, it has never let me down.

Turning now to the Montauk daisies, we should begin by mentioning that they are not daisies, although they are probably called that because of their bright white petals and yellow centers. Actually, many plants are referred to as daisies, that are really something else, probably for the same reason.

Now that we have said what they aren’t, we can proceed to what they are. Formerly called chrysanthemum, they are now classified as nipponanthemums. (Isn’t that a great word?)

We’ll begin there next week, and perhaps by the time we finish, they will actually be in bloom. They are almost the last of the perennials to flower, followed only, as far as I know, by boltonia, which we will cover last.

Tip of the week: One of our garden sections in front our house, unprotected from the deer, was, unfortunately, discovered by them this week. They ravaged our brand new hydrangea paniculata and chomped all of the New Guinea impatiens. What was interesting was that in one small area where the impatiens were interplanted with begonias — not tuberous begonias but the regular kind — the begonias were left alone. Worth considering.