Regional Gardening Reports :: National Gardening Association

In the Garden:
May, 2011
Regional Report

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Ephemeral lesser celandine is sweetly heart-shaped, but it's really a brute crowding out beauties like this primrose.

Lessening Lesser Celandine

Most of us gardeners like a challenge. We'll turn that gravel slope into an awesome alpine rock garden or a muddy hole into an environmentally beneficial rain garden.

Removing invasive, tuberous plants such as lesser celandine, goutweed, and Japanese knotweed poses a difficult quandary. These exotic plants overrun native ephemeral beauties such as Dutchman's breeches, trillium, trout lily,and Virginia bluebells. Unfortunately, these invasives are ecological threats not effectively managed by hand removal or with organic, least toxic products.

Last week a potential client invited me to see her garden and offer suggestions. Her back yard had such potential -- a spacious brick patio and two brick-edged beds reminiscent of a colonial garden -- as well as a huge obstacle! Lesser celandine, also called fig buttercup (Ranunculus ficaria), ran rampant. Shiny, heart-shaped leaves completely covered flower beds front and rear. They poked from between patio and pathway bricks. The property owner proudly noted a struggling rose and a couple perennials pushing their way through the dense blanket.

"What should we plant and when can we start?" she asked eagerly. I took some deep breaths. "Not any time soon," I answered. "The lesser celandine must go before I plant anything. That will involve herbicide applications for two, maybe three springs. In the meantime, how about planting in containers?" I suggested.

She said several years ago she paid someone $300 to pull out the weed. I bent, yanked a sample and showed her the bulblets along the above-ground stem and the tenacious tuberous root. The more you pull, the more it spreads. Tubers and bulblets scatter with each tug.

Hand weeding (aka manual control) may be effective for small areas if EVERY bulblet and tuber are removed, reads the Pennsylvania Department of Conservation and Natural Resources (DCNR) Exotic Plant Tutorial for Natural Land Managers. Mechanical removal requires the same technique but minimal soil disturbance; that's not recommended. "No biological control agents are currently available for lesser celandine," according to the DCNR.

The DCNR notes that lesser celandine is very difficult to control but can be managed with persistence over time using site-appropriate methods. "While manual methods are possible for some (small) infestations, the use of systemic herbicide kills the entire plant tip to root and minimizes soil disturbance."

Successfully eliminating lesser celandine involves specifically timed herbicide applications on green leaves for several successive springs. The DCNR instructs: "The window of opportunity for controlling lesser celandine is very short, due to its life cycle." To kill celandine and not kill native wildflower species, "herbicide should be applied in late winter-early spring (March through May). Apply a 1.5% rate of a 39 to 41% glyphosate isopropylamine salt mixed with water and a non-ionic surfactant to foliage." Glyphosate is a systemic herbicide. The plant absorbs the active ingredient, which moves to the roots, killing the plant in one to two weeks.

Yes, next spring you'll see leaves from bulblets missed this year. Treat those and any leaves in springs to follow. With time and treatment, you will have less lesser celandine.

NGA urges readers to follow state requirements and read and follow label directions and precautions carefully when using any pesticide or herbicide. Consult your local Cooperative Extension Service for information on specific product recommendations.

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