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Fielding Questions: Mystery plant ID, growing sweet stevia plant, killing daylilies

In this week's Fielding Questions, Don Kinzler identifies a mystery vine, offers tips on harvesting stevia and give guidance on removing unwanted daylilies.

110522.F.FF.FIELDINGQUESTIONS
A reader asks gardening columnist Don Kinzler to identify this vine growing in his dogwood plant.
Contributed / Dale G.
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Q: There’s a vine growing in our dogwoods and it’s spreading. Can you identify it? – Dale G.

A: The vine is wild grapevine, sometimes called riverbank grape. These woody vines can become very tall, using nearby trees and shrubs as support, and have been known to smother plants over which they’re climbing.

If sunlight is sufficient, wild grapevines produce clusters of small, dark, bluish-black grapes that are normally very sour, but edible. Birds eating grapes and dropping the seed elsewhere is why these grape vines pop up in unexpected places.

Because wild grapevine can be invasive, most opt to remove it, if found growing in the home landscape. The best month for control is September, with May and June being next best. Herbicides containing the active ingredient triclopyr or glyphosate can be effective.

When treating the grapevines with herbicide, care must be taken not to contact desirable plants. Instead of spraying, mix the herbicide in a bucket and dip as many vines as possible into the solution. Or, locate the base of the vine, cut at ground level and treat the cut surface immediately with herbicide.

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If herbicide use isn’t possible or desirable, digging is an option.

Q: I grew a stevia plant. Can I dry the green leaves and use them crushed as an alternative sweetener? – Audrey P.

A: Stevia is an herb used as a sweetener for thousands of years by native Central and South American people, although it’s only gained popularity in the United States in the past several decades and was approved by the Food and Drug Administration in 2008.

Stevia leaves are many times sweeter than white sugar, yet have no calories or carbohydrates. To be used in baking or cooking, leaves are dried and finely ground. Leaves can be used as sweeteners for drinks, either fresh or dried, especially in hot drinks, as the sweetening effect is intensified.

Stevia can be grown either in containers or in-ground gardens. The plants will become larger if stevia seeds are started in early March indoors, and transplanted outdoors in late May. Plants can become two feet high.

Harvest stevia when a few flower buds have appeared but before they’ve opened. If most flowers have blossomed, the plants and leaves develop a bitter aftertaste. Harvest in the morning when the sugar content is highest.

Q: Do you have any suggestions how to kill daylilies? Mine have spread through my flower garden and are taking over. I’d like to get rid of all of them. – Esther O.

A: Some older varieties of daylilies were recommended for planting where little else would grow. They had small flowers, spread tenaciously and I’m not surprised they’ve invaded the rest of the flower garden.

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Newer varieties of daylilies have much larger flowers, more vibrant colors and remain in clumps, increasing only gently, without invading their surroundings.

Unfortunately, there are no products that will selectively kill the invasive daylilies without killing other perennials that might be intermingled. In areas that are exclusively daylilies, herbicides containing the active ingredient triclopyr would be effective. Glyphosate, the active ingredient in original Roundup and other brands, could be tried, but I’ve heard reports of some older daylilies being resistant.

For an herbicide-free method, smother the daylilies with black plastic or cardboard covered with shredded bark. The material will need to remain in place for at least one growing season, possibly more, until the roots expend the life supply of stored energy.

If the daylilies have spread into the centers of other desirable perennials, herbicide use is too risky. You might need to dig up the perennials, separate out any daylily roots, and replant the desirable perennials, after first raking the soil clean of any daylily remnants.

More gardening columns from Don Kinzler

If you have a gardening or lawn care question, email Don Kinzler, NDSU Extension-Cass County, at donald.kinzler@ndsu.edu . Questions with broad appeal may be published, so please include your name, city and state for appropriate advice.

Don Kinzler, a lifelong gardener, is the horticulturist with North Dakota State University Extension for Cass County. Readers can reach him at donald.kinzler@ndsu.edu.
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