My hydrangea plants get black spots on the leaves. Some are in full sun and others in the shade. What can I do to prevent this?
The Gardener’s Answer
Hi, Charlie in Kentucky: Black spot on hydrangeas is caused from a fungus. There are a couple of different possibilities and without seeing your plants I can’t say for certain which one you are dealing with, but the good news is that it rarely kills the plant. It certainly does not look pretty and if left alone can spread throughout the plant so sanitation is important in terms of control. You will want to watch new growth as it emerges this spring and take a sample to your county Extension service or a local garden center to have the fungus identified for control purposes. Be sure to clean up all plant debris around your hydrangeas as the spores can spread if left alone. Avoid overhead watering since moisture left on plant foliage can lead to disease issues. If you do need to water it is always best to do so in the morning. This way if moisture does get on the foliage it will have time to dry before nightfall. Good sanitation practices usually keep fungus problems in check but if your hydrangeas are suffering from a severe outbreak then a fungicide may be applied. Removing all infected foliage and keeping the space around your shrubs clean will help prevent future spread. Make sure your plants have enough nitrogen to maintain steady growth, and a layer of mulch helps keep the moisture in, the weeds down, and in your case will help prevent spores from bouncing back up onto your plant when it rains.