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Too much rain stresses Indiana garden plants

Leaf spot on oakleaf hydrangea. (C) Jo Ellen Meyers Sharp

Leaf spot on oakleaf hydrangea. (C) Jo Ellen Meyers Sharp

With all of the rain and cool temperatures we’ve had, the plants are ripe for a couple of problems gardeners should be on the look out for.

Rot, leaf spots and other types of disease may appear on vegetables, shrubs, perennials and some annuals. Many fungus diseases are soil borne and are splashed onto plants with the rain or overhead watering. Rot may develop where the stem of the plant meets the soil.

Some perennials, such as garden phlox (Phlox paniculata), bee balm (Monarda) and Coreopsis are more susceptible to powdery mildew or other fungus problems than others.

Shrubs, such as Hydrangea, lilac (Syringa), ninebark (Physocarpus) and roses (Rosa) also can be affected by leaf spots and mildew.

In the annual category, million bells petunias (Calibrachoa), snapdragons (Antirrhinum majus), Begonia and succulents may be subject to rot with too much rain. Tomato (Solanum lycopersicum), basil (Ocimum basilicum), rosemary (Rosmarinus officinalis) also may get diseased with all of the rain.

Too much rain rotted million bells (Calibrachoa). (C) Jo Ellen Meyers Sharp

Too much rain rotted million bells (Calibrachoa). (C) Jo Ellen Meyers Sharp

What to do? Fungicides do not get rid of the disease on leaves but may prevent the disease from taking hold on new growth. There natural fungicides on the market, including copper or sulfur fungicide or neem oil.

To help prevent rot, make sure plants have good drainage, but once it’s on a plant, it is usually fatal.

The rain also has encouraged a lot of growth on all kinds of plant. That fresh new growth is an invitation for certain insects, such as aphids, which can distort or stunt leaves and flower buds. Spray affected plants with a strong stream from the hose to knock off the insects. A treatment of insecticidal soap may be necessary if aphids or other soft-bodied insects return in great numbers.

Too much rain also can drown plants, decrease the number of flowers and slow fruit and vegetable development. If needed, apply an all-purpose fertilizer according to label directions to replenish nutrients being washed away by the rain.

Tour gardens July 9 to see native plants in the landscape

July 9, 2011
Butterfly weed (Asclepias tuberosa). Photo courtesy Wildflower.org

Butterfly weed (Asclepias tuberosa) is a garden-worthy native plant. Photo courtesy Wildflower.org

The Indiana Native Plant and Wildflower Society annual garden tour will be July 9, 2011 in the Indianapolis and Lafayette area. The tour is a great way to see what native plants look like in a residential landscape. The tour is free, but registration is required to get the locations.