One of the most common symptoms that I see during this type of weather is a reddening of the foliage, especially on petunias and other annuals.
This reddening is caused by a phosphorus deficiency. Don’t fertilize. Chances are that there is plenty of phosphorus in your soil, but it’s not in a form that is available to plants.
When soil temperatures are cold, phosphorus is not available to the plants. The symptoms usually show up as a reddening of the older foliage.
It’s usually not a big deal or problem because as soon as the weather warms up and soil temperatures go up again, the phosphorus becomes available to the plant and the foliage greens up again.
The other issue that you might find on annual with our recent cool damp weather is botrytis or gray mold.
This disease affects a wide array of perennials and annuals and some vegetables and fruits and thrives in cool, rainy weather.
It’s not usually damaging if you are paying attention to it. If you let it go or if we have rain for a long period of time, it can cause some problems.
I am guessing that you all have experienced this at some point in time but weren’t familiar with the disease.
Watch for brown spots on herbaceous (green) tissue and look for silver-gray spores on the dead or dying tissue. It looks like it sounds — a gray mold.
It affects all parts of the plant except for the root system. I usually see it on the flowers and buds and sometimes on the leaves.
The good news about botrytis is that when the weather changes. In the meantime, hand-pick flowers, leaves and other plant parts that are affected as they will continue to spread the spores through splashing rain and the wind.
Avoid doing this when the plants are wet as the problem spreads faster.
Rapid drying of plants and good air circulation helps to prevent this disease, and it’s not one that I recommend using fungicides.
Good sanitation practices in the fall also help to prevent major outbreaks of this disease when weather conditions are right. Like now unfortunately.
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