Question of the Week
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Thanks, Lisa Maddox, for this great question! This happens to a lot of gardeners, so we appreciate your pictures to help us all out.
So, here's the deal: Lisa's having problems with her annual Vinca, commonly called periwinkle. This is a great summer annual that likes the sun and gives us easy-care joyous color until frost.
But, if you plant them too early, like in March or April, they can simply rot on you. Yes, the garden centers push them at you then, but these are heat-lovers. Even if we get scalding hot days in April, the soil is way too cool. And the nights are still cool and moist, which leads to disease.
Lisa's symptoms: the plants turn brown and start to wilt. The disease here is either Pythium or Phytopthora. Those are both soil-borne diseases known as water-molds. These diseases have spores that are motile in water, and in the spring rain or by watering your plants from above, you can actually splash those spores onto your plant from the soil.
Those spores are pretty much ubiquitous and so the disease will remain in your soil, but you can prevent the problem in the future.
First, don't plant periwinkle or other heat-loving annuals (like caladiums) until our days are reliably in the 80s, and that's usually about mid- to-late May. Next, make sure you mulch around your plants. That separates them from the soil surface, and thus, from those disease spores. And be careful to water only the ground so that water doesn't splash from your soil onto your plant.