Answer: Some daylilies such as the orange flowered tawny daylily (Hemerocallis fulva) can become invasive, especially in rich and/or moist soil. They spread by underground roots. To prevent it from spreading further you need to maintain a cut edge and dig them out along the border periodically. To control it more permanently you need to dig it out by the roots as well as prevent it from setting seeds by cutting off the spent blooms. Or, you would use an herbicide. If you opt for that, use one containing glyphosate and carefully read and follow all of the label directions. They may reappear requiring a second treatment. Good luck!
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