How Do You Treat Yellow Leaves On Hydrangeas.
With careful observation of the leaves, a person can often diagnose health problems in hydrangeas.In a home landscape, brown spots on the leaves are usually caused by a fungus or bacteria.In most cases, the fungus or bacteria does not threaten the life of the plant, but the spots can be unattractive.These spots usually appear annually toward the end of the summer and fall.The following spring, the leaves emerge unaffected, and the spots from the previous year do not affect the plant’s ability to bloom.There are two types of fungal diseases can infect hydrangeas - cercospora leaf spot and anthracnose.Spots on the hydrangea macrophylla will sometimes have tan or gray centers with brown or purple border halos.In most cases, fungus growing on hydrangea leaves will not kill the plant.Leaf spots on hydrangeas caused by bacteria are from the pathogen Xanthomonas campestris.Similar to cercospora, this will typically start at the base of the plant on the lower leaves, and will be either purple or red in color.This type of bacteria primarily impact Hydrangea quercifolia, arborescens and macrophylla.You can help control brown spot by keeping the ground under the hydrangea free from leaf debris and by occasionally cutting off the old stems to allow air to circulate through the plant.We also recommend removing all diseased and dead leaves off of the plants, to help prevent the spread of the leaf spot.During the growing season (the spring or the summer) if hydrangea leaves unexpectedly turn yellow and then brown and begin to fall off, a problem with the roots is usually the cause.In addition to these symptoms, keeping the plant too wet can lead to root rot and even death.If a plant has been allowed to dry out, the first step to recovery is to thoroughly water the entire root ball.If it is still in a pot, try setting the plant in a tub of water up to the rim until the dry roots have been completely soaked.So, allow time between each watering for the soil to dry out slightly and for the roots to regenerate.Hydrangeas growing in a pot or newly planted in the ground have roots that are especially vulnerable to strong applications of fertilizer.Aluminum sulfate, which is sometimes added to the soil to change the color of hydrangea blooms, also can cause root damage if applied too liberally.After root-burn, do not fertilize again until the plant appears healthy, suggesting that it has developed a well-established root system.Also, water in the morning so the leaves can dry out during the day and before the temperature drops at night.But this is natural and normal and, unless the freeze occurs after abnormally high temperatures, it should not harm the hydrangea at all.So, unless one lives in a very cold climate, hydrangeas do not need to be covered when normal winter temperatures are experienced.Once the sap starts rising in the stems of a hydrangea, the plant’s ability to withstand cold temperatures is greatly reduced.Tennessee State University College of Agriculture, Human & Natural Sciences - Foliar Diseases of Hydrangeas, Dr.
