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Poplar problems, purslane control, pea planting pointers

"Fielding Questions" columnist Don Kinzler replies to a reader concerned his cottonwood is dying prematurely.

Poplar July 16, 2022.jpg
A reader is concerned his cottonwood is prematurely dying.
Contributed / Don Kinzler
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Q: We have a cottonwood in our yard, and we noticed last week that a few branches are dying. The tree is approximately 25-30 years old so I can’t imagine that the tree is dying. We were wondering if this was a common thing or could it be some sort of disease? – Mark P.

A: The poplar genus of plants is a large tree group that includes the native cottonwood, quaking aspen, and many hybrid types. All are fast growing.

A rule of nature seems to dictate that fast-growing trees generally have shorter life spans, and slow-growing trees, like oaks, have long lives. Although the native cottonwood can be long-lived, many of the other fast-growing poplars have relatively short lives.

Most poplars planted in urban or windbreak sites are hybrid poplars, nicknamed “cottonless cottonwoods” which were selected to be free from the cottony seed that can inundate yards and window screens with the fluffy material.

These hybrid poplars have a definite lifespan, which seems to be 30 to 40 years, before they succumb to problems resulting in dead branches, which become common throughout the tree, resulting in eventual death. The tree in the photo you sent, Mark, is most likely following the common lifespan trend of these poplars.

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There’s really nothing that can be done to fight what seems to be predetermined. You could prune out dead branches as they appear to improve the appearance. My wife and two sons recently removed five of these 40-year-old poplars at our own home.

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Q: I have a lot of purslane in my flower bed. I pull them out and have for several years as soon as I see them, but I’m losing the battle. Is there something I can use to control it? I remember years ago hearing about a new product to control weeds that came from seed. It had treflan in it. Is that still on the market? Al S.

A: Purslane is a plague, and many of us spend a great deal of time attempting to eradicate it from our gardens and flowerbeds. Any of these ground-hugging plants that escapes our efforts can spread hundreds of thousands of seed that can persist in the soil for another 40 years.

Luckily, the pre-emergent herbicide Preen, which contains the active ingredient you mentioned, is quite effective. It doesn't have any effect on purslane that's already growing, but it kills purslane seed as it’s germinating.

For flowerbeds, Preen is best applied in the spring after transplanting flower plants into flowerbed soil that’s been tilled, or otherwise free of weed growth. Apply the granules following label directions.

Exposure to sunlight can cause Preen to loose it’s effectiveness, so immediately after applying, the granules should either be incorporated very shallowly into the soil surface, or watered in.

Preen can break the purslane’s cycle, but since there's usually a plentiful bank of seeds in the soil, it takes a number of years before the seeds totally become extinct in one's yard.

Q: I was prevented from planting peas in April, and from my experience any peas planted after May are difficult to get to grow. Do you have any tips for successful planting now? Lincoln peas are our go-to variety without exception. - Mike D.

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A: As you know, peas like cool soil, so planting in mid-summer can be a challenge, but there are a few key recommendations that can yield great success. In the row or area you intend to plant, work some peat moss into the top several inches. Peat not only helps hold moisture, and makes the soil more mellow, but it also keeps the soil cooler.

Next, dig a trench about three inches deep, and plant the seeds in the bottom at the proper one-inch depth. When the seeds sprout and the plants grow, gradually fill in the trench, which keeps the roots in a soil zone that’s a little cooler and moister.

Mulch the soil surface after the peas emerge. The mulch can be straw, grass clippings from a non-herbicide lawn, or peatmoss wetted down so it doesn't blow. Two to three inches of mulch will keep the soil moist and moderates the heat.

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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