I used to think that asters were weedy plants that were too wild for a garden. I always thought they looked great mixed in with a field of goldenrod, though.
Then I got a job at a greenhouse, potting up bare-root plants. After the aster roots were potted, I picked through the leavings and got some root bits. That fall, much to my surprise, every root bit that had a bud on it came up with a vengeance, and what a pretty vengeance it was.
I have New England asters, a native species that is widely distributed. They have daisy-like flowers with lavender petals, and they bloom like mad through fall, much to the delight of the insects that frequent the flowers for nectar.
Asters are known for spreading. In fact, one of my aster clumps has been busy growing up a little slope near the back of my garden. Some varieties of asters tend to get a little wild, which is why they are often seen as weeds.
Asters spread through underground runners, and the native species, such as the New England and New York varieties, will reseed. Gardeners should keep that in mind when planting them.
The New England and New York varieties will grow true to seed if a gardener wants more plants. However, if using the hybrid aster varieties, such as Harrington's Pink, Alma Potschke, Marie Ballard or Crimson Brocade, gardeners should pull up the seedlings. This should be done because the plants that grow from these seedlings won't look as nice as the original.
If asters begin taking over the garden, keep them within a boundary. To do this, pull or dig out the new shoots, or divide the plants. Some gardeners divide asters each year to keep them within bounds, and other gardeners divide them every few years.
It is important, however, not to divide asters in the fall, when they are flowering and setting seed. Divide them in the spring, during root and leaf development.
Some people consider asters to be weeds. But even the regal calla lily is considered a weed in Africa, because the plant clogs up waterways.
I guess it just depends on how one looks at it.