Garden Q&A: Geraniums don't like our hot, humid summers

My geraniums have developed black spots on their leaves. Can you tell me what's wrong with them?

Geraniums are among the most loved plants around the world because they flower for a long period of time and have beautiful foliage. Here in Florida, they face a real challenge surviving the hot, wet, humid weather of summer.

Because they have many small hairs on their leaves, water drops get trapped on the leaves. The wet spots on the leaves provide an avenue for fungi and bacteria to invade the plant and infect it.

Some homeowners deal with this by cutting the plants back to a few inches tall, and allow it grow out. This removes the entry point for the disease and by the time the plant has flushed out sufficiently, hopefully the weather will have shifted to our cooler, drier fall weather.

Whether your plant is suffering from a bacterial blight (xanthomonas x pelargonii) or a fungal infection (most likely alternaria), some basic safeguards will help.

Remove all diseased or damaged leaves and discard them to prevent spores or other reproductive items from spreading the disease. Water the soil in the pot, not the foliage, to reduce the amount of moisture on the leaves. Since your plants are in pots, move them to a place where sprinklers and rainfall do not wet the leaves. Make sure there is good air movement around the plant to help dry the leaves.

It's really important to remove the flowers after they finish, otherwise they serve as hosts for bacteria and fungi.

Fertilizer will be helpful in stimulating the plant to grow new leaves and stems. Geraniums need regular fertilization to grow well anyway. You can also apply a copper-based fungicide to help bring the disease under control.

I often park under a maple tree and am finding globs of sap on my car. Should the tree be leaking sap? Can I stop it?

The causes of sap leakage are many, and several different families of trees are frequent offenders. If the point of leakage is on the trunk of the tree or major limbs, it will usually show up as a dark streak down the tree.

Borers make holes that allow sap to leak out. So do sapsuckers, the birds that eat both sap from the trees and the insects that get stuck in the sap.

If the tree has wounds on the branches, these will also leak sap. Poorly made cuts on the tips of the branches will cause sap leakage from the branch tips.

Remember that sap is made up of water, minerals and other nutrients and sugars that the leaves have produced. We use saps for many products, and squirrels also find them equally tasty and nutritious. If you have a large population of squirrels, they may well be the culprits.

None of these are things you can prevent. But a couple of things will make the sap easier to remove from your car.

Keep a good coat of wax on the car surfaces, which will prevent the sap from sticking tightly to the car. And wash the car often. As the sap dries out the surface of hot car, it becomes thicker and more difficult to remove. Persistence and a bug and sap removing product will remove it.

How much water do my citrus trees need? It's been awful hot out there.

This is a critical time for citrus trees. The developing fruit requires a lot of water to finish growing well. If you skimp on water, the peel will become thicker to conserve water. Then, when fall rains come, the fruit will expand rapidly without the peel being able to expand. The fruit will crack. It usually happens several weeks before the fruit is ripe, so the blemished fruits aren't even harvestable.

Protect yourself now. Once a week, lay a hose down at the base of the plant and let it run for 10 minutes. Don't let it run for longer periods or you run the risk of developing one of the rot diseases that can kill citrus trees. If you can keep your trees well watered now, you will have better fruit in a couple of months.

Becky Wern is a master gardener with the Duval County Extension Service and the University of Florida/IFAS.