'Summer Snow' Gardenia Browning Leaves
I just purchased 3 summer snow gardenia shrubs (Gardenia jasminoides 'BAB 1183') for the front of my homes garden bed. The two on the edges are doing just fine, but the middle one leaves have started to turn brown towards the back side of the plant. The leaves feel soft, not dried out. They have only been planted for about 4-5 days. We have had rain and I have watered them. They were planted with total compost mixed with the soil that was already there. The spot gets a lot of morning sun until about 1:00-2:00 and then they are in partial shade. I have not seen evidence of any bugs or anything chewing on the leaves. There is some slight yellowing on a few leaves, as well.
This looks like sunscald damage. Your plants may not have been acclimated and they are reacting to the new conditions they are in. We notice more of the browning near the wall -- possibly from radiated heat (stress). This does not look like a symptom of a disease or pest problem.
Since your plants were put in just a week ago, give them time to get acclimated. Some new plants can experience a period of transplant shock. The plants need time to establish their root system. All you can do is remove the affected leaves. Keep the plant watered during dry periods. Make sure there is not too much mulch -- it should be only 2-3" deep and avoid touching the plant stems. New growth will be a sign that the plants are establishing successfully.