I am trying to get rid of a patch of daylilies with orange flowers and replace them with an assortment of daylilies with different colors. For the last two years I have dug out the orange-colored daylilies and planted new varieties. Once again only the orange ones come up and bloom. What am I doing wrong?
— Jessica Bennett, Chicago
There are certain weeds that I find incredibly annoying to deal with in my garden. This daylily is one of them as it is very difficult to eradicate. You probably have common daylily (Hemerocallis fulva) in your garden. This plant is considered invasive in the Chicago area and very difficult to eradicate because of its thick, tuberous roots. The plant will start growing again from any roots left in the ground. You are probably leaving enough roots in the ground after you dig the orange daylilies out for them to resprout vigorously and overtake the newly planted daylilies. Gardeners who dig out entire daylily plants and put them in a home compost pile unknowingly spread this invasive plant too. Most home compost piles do not generate enough heat to kill the roots of this plant.
There is a patch of this daylily growing along the back of my garden in a very shady location, so it does not flower. It comes in from the neighbor’s garden. It spreads very slowly, so I monitor it and spray the outer edges once in a while with herbicide to check its growth. From a distance it’s green, so I live with it as the deep shade checks its growth.
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Try digging out all the orange-colored daylilies again. Wait for them to resprout and then dig them out again. Keep at this until there are no orange daylilies resprouting before installing your new plants. The process will probably take six to eight weeks to complete. Keep your new daylilies in their pots in a sunny area of your garden. This should ensure success in growing the new varieties of daylilies and any other perennials you plant. If the new daylilies need to be planted earlier, be sure to mark them, as they will look like the weedy daylily. This way you can easily identify any of the orange daylilies that return. You can also spray the invasive daylilies with a non-selective herbicide such as glyphosate to kill them. Dig out the roots once the tops of the plant have turned brown. The herbicide will take at least two weeks to work. It is best to remain vigilant even after this for any returning orange daylily growth.
For more plant advice, contact the Plant Information Service at the Chicago Botanic Garden at [email protected]. Tim Johnson is senior director of horticulture at the Chicago Botanic Garden.