Hello. I am noticing some of the leaves on my climbing hydrangea & potted ferns are turning a rust colour.
Not seeing any visible insects and am wondering if you might be able to suggest what is going on.
There are a number of reasons why your hydrangea leaves could be turning brown both abiotic (environmental) and biotic ( fungal).
The first and obious reason that your leaves are turning brown is they are getting too much sun. Hydrangeas prefer to be grown in a spot where they receive morning / evening sun but are protected from the intense rays of the afternoon sun. You do not mention where your climbing hydrangea is positioned in your garden. As well as being scorched, hydrangea leaves will turn brown if they’re left to wilt too often in the hot weather. We have had significantly less rainfall this spring than in the previous summer. Have you been supplementing with regular watering? To avoid frequent wilting make sure to give your hydrangea a good drink of water every few days during periods of extrenme heat. A couple inches of mulch around the base of the plant (making sure to keep the mulch 3″away from the trunk) will help with moisture retention.
Time of day when you water could also lead to leaf scorch. Water which has been left on the leaves of your plants and has not been allowed to evaporate can cause leaf sorch and lead to fungal problems. Take care when watering your hydrangea, making sure to water the soil and roots only rather than spraying all over the foliage as well. If you need to spray your leaves do so in the early morning so that the water has time to evaporate.
Another factor could be fungal damage. If this is the case telltale blemishes start to show up: brown pockmarks and a general appearance of bruising and damage to the leaf. Fungal damage can cause browning but you may also see yellows and purples. The best way to avoid fungal damage is to remove debris and dead plant material rom beneath the plant and if possible to improve air circulation around your plant.
from your photograph, I do not believe that the browning of your leaves is caused by fungal infection. Instead I believe it is a result of leaf scorch: too mich sun and too little watering .
We have numerous posts dealing with climbing hydrangeas which you cand here.
Good Luck with your