Hydrangea yellowing leaves follow up

Asked July 17, 2018, 9:18 AM EDT

I am following up on my previous question about yellowing hydrangea leaves, with pictures attached. The lighter picture is the underside of an Annabelle hydrangea. The darker one is the underside of a little lime. My biggest challenge is that I can’t tell if I am over or under watering. I have read that in clay soils, water builds up around the roots and can cause disease, but it has also been extremely dry. I have tried frequent (twice a day) but also less frequent watering (longer, every other day). I amended my soil quite a lot with leafgro and some pine bark when I planted the hydrangeas, so I hope it is not an issue with the soil but perhaps it is.

Prince George's County Maryland

1 Response

We viewed your photos. We see leaves that are shaded and leaf senescence (deteriorating with age) which can be normal. The new growth looks okay and do not see signs of insects or disease issues.

Hydrangeas like a moist well drained soil amended with some organic matter. Make sure mulch is no thicker than several inches and away from the base of the plant. If planted in full sun, they will require more moisture. Check the soil moisture of newly planted shrubs at least once a week and maybe more. You may need to probe with a screwdriver and water at least 4-6 inches deep. Let the soil dry out slightly before watering again.

If the plants were just planted this season and the roots were confined within the container, they may have trouble spreading into the surrounding soil. It can be hard to keep the plant watered. If so, the roots should be spread out into the native soil.
Also, if the soil is clay and you added topsoil and a lot of organic matter to the planting hole only this can create a 'bathtub effect'. Water sits in the planting hole and drowns the plant. The surrounding clay (which doesn't drain well) won't let the rain out. The organic material should be incorporated into the eventual root zone of the plant not just the planting hole.
Here is our website on the planting process and after care https://extension.umd.edu/hgic/trees-and-shrubs/selection-purchasing-planting-and-care