Gardening -- A reader wonders about lack of apples on her trees

  • Article by: NANCY ROSE , Contributing Writer
  • Updated: February 13, 2002 - 10:00 PM

QThere is very little fruit on neighborhood crab-apple trees that usually have fruit on them all winter. Has this happened in other areas? If so, what is the cause?

AFrom observing the many crab-apple trees at the Minnesota Landscape Arboretum, I'd have to agree that this has not been an outstanding winter for colorful crab-apple fruit. A number of crab-apple cultivars tend to be alternate-year bearers; that is, they produce heavy crops of fruit one year, then a sparse crop the next. Although this could explain lack of fruit on a few crab-apple trees, I think the main reason has been the extraordinarily warm weather we've had this winter.

The normally persistent fruit of some crab-apple varieties continued to ripen and soften in the warm November and December temperatures, instead of being frozen. As a comparison, imagine the difference between a fresh cranberry left out on the kitchen counter and a fresh one put into a freezer. The frozen one would stay red and firm longer.

Birds are another factor. I don't ever remember seeing cedar waxwings and robins, and lots of them, staying here into January as they did this year. These birds love small crab-apple fruits and often come through in early spring to gobble up all the softening crab-apple fruit. This year the fruit softened earlier, and it was warm enough for the birds to stay around, leading to lots of fruit-stuffed birds and bare crab-apple tree branches.

QI have heard about buckthorn being an invasive weed, and I have to pull buckthorn seedlings out of my garden all the time. Recently I heard about garlic mustard and creeping bellflower becoming weed problems. Are these weeds already in Minnesota, and how would I get rid of them?

AWhile invasive plants have been around for centuries, the issue has really gained prominence in the past few years. While invasive plants can be an irritation to gardeners, these plants can have a more severe impact in natural areas. The most aggressive invasive plants take over natural habitats and push out native plant species. The loss of native species can negatively affect birds and other wildlife.

In Minnesota, two plants that have proven particularly invasive are buckthorn and purple loosestrife. Buckthorn, including common buckthorn (Rhamnus cathartica) and glossy buckthorn (Rhamnus frangula), has invaded native woodlands, forming a dense understory layer. It is also quite adaptable to urban areas and sprouts in gardens, fence rows and alleys. As anyone who has ever tried to pull up a buckthorn seedling knows, this woody plant develops a large and tenacious root system, and even small seedlings vigorously resist being pulled up. Nurseries no longer sell it because of its invasive nature.

Purple loosestrife (Lythrum salicaria) is an herbaceous perennial that has invaded wetlands and lake edges inthe state. This invasive plant is most noticeable in summer when its bright pinkish-purple flower spikes bloom. Purple loosestrife is particularly difficult to eradicate because of where it grows; it's hard to completely dig the plants out of wetland soils, and many herbicides cannot be used near water because of the possibility of pollution. Research is underway to see whether an imported weevil that feeds on purple loosestrife can reduce its spread.

Garlic mustard (Alliaria petiolata) is an aggressive weed that has been moving north and is becoming a problem around the Twin Cities. It is an herbaceous plant that produces small white flowers early in the spring. Because it gets an early start, garlic mustard's many seeds grow before other plants have a chance to compete. Garlic mustard can form dense stands, crowding out native plants. A combination of hand pulling and careful herbicide use should control it.

Creeping bellflower (Campanula rapunculoides) is a less aggressive weed, but it can be a problem in some areas. A U.S. Forest Service listing of invasive plants puts this plant in the category of widespread nonnative plants that are not aggressive invaders of undisturbed natural areas but can invade already disturbed areas. I have not heard that creeping bellflower is a big problem in Minnesota, but it is hardy to zone 3 so it has the potential to survive in most of the state.

Your question brings up an important issue in the whole invasive plants debate. Invasiveness of any plant species can vary greatly in different regions. Purple loosestrife is a particular problem in this state because we have so much ideal growing habitat for this species. In some parts of the country, commonly used landscape plants such as Norway maple (Acer platanoides), Japanese barberry (Berberis thunbergii), Tatarian honeysuckle (Lonicera tatarica) and burning bush (Euonymus alatus) have become invasive. English ivy (Hedera helix), a widely used ground cover, is an invasive pest in the Pacific Northwest, but severe winter temperatures in our area make English ivy marginally hardy and therefore noninvasive.

What should gardeners do about invasive plants? This is a difficult question, because landscape plants may become invasive slowly over a number of years, and the degree of invasiveness of any plant is often open for debate. Clearly, a plant such as garlic mustard has no ornamental value and should be removed to prevent its spread. Other plants may need to be evaluated case by case.

QI planted malva in a front-yard flower bed and it has taken over. It's even growing into the grass. Is there a way to contain it?

AThe mallows (Malva) comprise a diverse group of plants, ranging from pernicious garden weeds such as common mallow (Malva neglecta) to attractive perennials such as hollyhock mallow (Malva alcea 'Fastigiata').

You didn't mention which mallow you have, but I'll guess that it is either hollyhock mallow, which grows about 2 feet tall and bears many light-pink flowers, or Malva sylvestris 'Zebrina', which grows about 2 to 2 1/2 feet tall and has white to light-lavender flowers with distinct purple streaks radiating out toward the petal edges.

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