I planted a new limelight hydrangea late Spring in my backyard in north east Scarborough, I have been looking forward to it blooming and it has finally started to do so. I though noticed yellow and brown leaves as of a few days ago. They are falling of the tree. Is the tree getting too much sun, too much water or not enough water?
Your question is well-worded … any of these could be the problem.
Although hydrangeas can grow in full sun or semi-shade happily, in the intense heat and high UV ratings we have been experiencing this summer, some leaves may be burned.
If the leaves have spots on them, that may indicate a fungal disease.
However, the picture seems to show that the soil at the base of the plant is muddy, while the surrounding area is dry. Overwatering can lead to root rot and shallow watering also puts the plant at risk.
Early morning is the best time to water. Watering thoroughly and infrequently will force the roots deep below the soil surface, and this helps protect them during hot, dry weather. Shallow watering will force the roots to the surface in search of water, and this will result in plants under stress. An application of 5-8 cm of mulch to the area will conserve moisture and cool the soil temperature.
And there may not be a problem at all … if the leaves that are turning yellow and falling off are primarily on the inside of the plant, that is not unusual. Your young plant is blooming very well and it may just be dropping some leaves to devote its energy to the flowers.