Tuesday, May 22, 2012

When bad things happen to good plants

Spring's weather fluctuations bring a host of problems in their wake. While barometric shifts and pollen barrages may trigger allergies, headaches, and arthritic flare-ups in humans, plants have problems too. Black spot, powdery mildews, red thread lawn molds and other common disorders can disfigure fresh new foliage and stunt the eager growth of spring.

The usual culprit is excess rain and cold nights. Lawns suffer because clay-based soils stay so damp they become anaerobic. Airless soil favors root rots and mossy growth while discouraging sturdy rooting in turf grasses. To bring a soggy lawn back to life, rake an inch of compost evenly over the grass. Do this now and you'll see an almost immediate improvement in turf quality. Do this each spring and every fall and in a few seasons, the renewed soil will support healthy, deep-rooted turf that resists red thread and molds.

Several studies carried out at have proven that compost does more to improve lawn health than the sadly typical regime of fertilizers and pesticides. That's because chemical treatments only affect symptoms, while regular applications of compost heal both sandy and clay-based soils, promoting turf health from the inside out.

The good news is that by choosing green lawn care, we actively promote a healthier environment on many levels. Instead of adding to landfills, we create a need for recycled green waste, which becomes wholesome compost. By using compost instead of chemicals, we do not add to the toxic chemical burdens that impair soil, air, and water quality. Rain that washes through our property carries away no dangerous residues to harm frogs or fish. Birds, bees, and butterflies that visit our gardens and lawns are not imperiled by toxins.

If the turf is thin and spotty, rake in compost then oversow with a regionally appropriate seed mix. Choose a shade-tolerant blend for any areas that get less than full sun, and try a playground blend for areas that get a lot of foot traffic.

Powdery mildew is widespread when a wet spring causes sudden shifts of warm and cold weather. Affected plants look as if the foliage is dusted with flour. Powdery mildew is usually caused by some combination of dry roots, high humidity, crowding and poor air circulation. It is very common to see it on plants growing too close to a house, especially under eaves.

To avoid powdery mildew, space plants generously and never plant anything where it will touch a structure at maturity. Leave an air space of 2-3 feet between any plants and your home or a wall. Set properly away from walls, plants grow better as air circulation and soil health improve.

Once black spot finds a garden, it is very difficult to eradicate. Personally, I compost any rose that remains susceptible, preferring to grow plants that thrive with natural care. Rugosa hybrids are high on that list, as are many modern shrub roses, including the Canadian-bred Explorer series. Of species roses, among the easiest to please are blue-leaved Rosa glauca, the ever-blooming R. chinensis, and sweetbrier, R. rubiginosa.

Healthy soil helps plants resist many foliage diseases, so give any sufferers a deep mulch of aged manure or compost. To reduce symptoms immediately, spray foliage with baking soda, adding insecticidal soap or horticultural oil as a sticking agent. Here's a recipe.


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