Ask Mr. Smarty Plants

Ratibida columnifera (upright prairie coneflower) is a perennial wildflower, native to the area around Kane Co., in the northeastern corner of Illinois. It ranges in size from 1 to 3 ft tall, and the tall, unleaved stem carrying the flowers well above the rest of the plant is one of the features most noticed, especially when the plant grows in fields or along roadsides. 

Plants have their genetic instructions in their seeds. If a plant is supposed to grow 3 ft. tall, there is no good reason besides severe drought or disease for it to do anything else. Plants' prime imperative is to reproduce themselves. In order to do that they must seed, and in order to seed, they must bloom. This principle means that you can sometimes get a plant to bloom more profusely by deadheading, or nipping off the bloom when it starts to wilt. However, this process takes a lot of energy, and there is no way of explaining to the plant that you will allow it to bloom, but it has to do it lower down on the stalk. If you cut the height in two, the plant will probably still try to bloom, but it is going to be trying to grow those longer bloom stalks, and in your climate, it is likely to be freezing weather before the plant manages that. 

We're assuming that you have your prairie coneflowers in a place where you wanted shorter plants, since you asked when you could move it. All the research we did indicated that, while perennial, this plant's recommended propagation is by seed. However, we believe it would be possible to divide the plant and replant it somewhere else. It should be trimmed back after the first freeze, but leave sticks or a marker so you will know where it is when you are ready to transplant. We would recommend you do this transplanting in Spring, after the ground begins to thaw. You appear to be in USDA Hardiness Zone 5a to 5b, which means you have average annual minimum temperatures of -20 to -10 deg. F. It would be harder on newly divided roots to cope with very cold temperatures soon after transplanting than with the gradual warming in the Spring. For more detail on the process, here is a website from About.com:Gardening on How to Divide Perennial Plants. 

From our Native Plant Image Gallery

Ratibida columnifera

Ratibida columnifera

Ratibida columnifera

Ratibida columnifera