Mountain Laurel leaves turning yellow and brown in the fall
Hi, I bought two mountain laurels last spring, and they looked OK all the summer, but at the end of September I noticed that some of the leaves are turning yellow or brown, and drop. I did not find any insects except for a couple of leafhopper assassin bugs, and some leaves are being eaten, but most of the leaves are solid, - just turning yellow or brown, and there are, maybe, a dozen of them on the ground around the plant. Maybe it's natural for mountain laurel to lose some of the leaves in the fall? There are some leaves that have brown patches (bot not spots), - like they are burnt, - but, on the whole, the plans look healthy. The plants are in partial shade, and the soil is a mixture of clay soil with some compost and peat moss, and I water them regularly, and there's a layer of mulch underneath. It doesn't look like leaf spots. Thank you.
There are a couple of possible reasons for the discoloration and leaf drop on your mountain laurel (Kalmia latifolia). First, check the planting depth. the top of the crown should be at, or just slightly higher than soil level, but no deeper. If the plants have settled you may need to lift them to correct the depth.
Next, get a soil test to check your soil pH. Mountain laurels prefer well-drained acidic soil (below pH 6.5). Often times the plants become chlorotic in alkaline soils because they cannot absorb enough iron. Your local extension office can direct you on getting a soil sample.
Two other issues are summer drought and winter wind. Mountain laurels do best in a partly shaded area with some protection from drought and wind. Be sure to mulch around the plants to keep the soil evenly moist. If wind becomes a problem, you may need to provide a windbreak or try a different location.
Here is an answer to a previous question that may be useful: