Ask Mr. Smarty Plants

There are two plants in our Native Plant Databas with the common name "Blackeyed Susan."

Rudbeckia hirta var. angustifolia (Blackeyed susan) According to this USDA Plant Profile Map, this plant grows only in southeastern states and Texas, so we conclude that what you are dealing with is Rudbeckia hirta var. pulcherrima (Blackeyed susan), which according to this USDA Plant Profile Map, grows just about everywhere, so we can assume that is the plant you are finding invasive. Mostly the Lady Bird Johnson Wildflower Center, home of Mr. Smarty Plants, is committed to the growth, propagation and protection of plants native not only to North America but to the area in which those plants have evolved. We are totally in favor of preventing the spread of non-native invasives, but obviously sometimes natives can be invasive, too, as you have discovered.

We did learn that the plant has rhizomatous roots, as you probably know. This makes eradication extremely difficult, as you also know. This plant is classified in our database as a biennial which can perennialize if it is happy. You must have a lot of happy plants. The biggest problem with rhizomatous roots is that if you don't eradicate every possible small underground stem, it will rise to grow again. This plant, of course, also propagates itself by seeding, so you have a double whammy. There is a possibility that what you have is a hybrid or species of the rudbeckia genus that is not in our database, but we are assuming that the same principle applies. When you ask about using a broad-spectrum herbicide, we tend to shudder because most gardeners want to apply it in a spray. Doing so means that, yes, you are going to damage other plants, but the poisons will not get down to the root of your problem (excuse the pun) because the spray is airborne.

We are frequently approached for a way to get rid of an invasive plant that seems to just keep coming back. Here is what we suggest: buy a small bottle of an undiluted broad-spectrum herbicide and some small disposable sponge paint brushes. Cut a plant down to the ground, and make sure no seedheads are left on the plant before you put it in the compost pile. Quickly, within five minutes, paint the cut root still in the ground with the herbicide. You must do it quickly because the root will be trying to heal itself over to protect the roots. This requires persistence and determination; learn to recognize the plant as soon as it pops its head up and treat immediately. Of course, you already know not to let any of the plants seed themselves out. You can still enjoy the blooms but they must be trimmed promptly, and Rudbeckia hirta var. pulcherrima (Blackeyed susan) blooms for several months.

Would you consider designating a "Blackeyed Susan Garden" and make lemonade out of your lemons?