Browning in the interior of leaves on houseplants can be caused by several situations including sunburn, fertilizer burn, salt or fluoride build-up, contact from cleaning products, or diseases such as powdery mildew. Sometimes without culturing in a lab it’s hard to pin it down. For leaves such as yours that show browning in between the veins on the leaves it can be narrowed down a bit since sunburn would present over the entire leaf surface, fertilizer burn would be likely to show along all edges, and contact from cleaning products would cover the entire surface of the leaf. So that narrows it down for your plant to sunburn (unlikely at this point on Cape Cod!), salt/fluoride build-up, or disease.
Of these three, we’re wondering about powdery mildew first because of the faint, grey appearance we see on the bottom and bottom right of the leaf. If you see this continuing to develop on the leaf, that may be the clue to the cause. Look under the leaf for signs of grey powder as well.
No matter what is the cause, remove all the leaves that look like this and throw them away. This will make the situation easier to monitor as well. Next, be sure that the health of the plant is supported by watering deeply less often (don’t just give a “lick and a promise – water the plant deeply when you water, soaking the entire root ball and letting the water drain into a saucer below. After a couple of hours empty that saucer so that the plant isn’t kept too wet.) Be sure the plant has good air circulation and the room that it’s in doesn’t go much below 60 degrees.
If it seems like powdery mildew isn’t the issue, perhaps this plant has been in the same pot for some time and there has been a build up of something that is causing the leaf issue. If this is the case, repot the plant and remove as much of the old soil as possible without harming the roots, and replace that with clean, new potting soil. Don’t start to fertilize for a month until the plant gets resettled. Consider using an organic fertilizer in the future.
If you see that powdery mildew could be the problem, get a fungicide that’s labeled for powdery mildew at your garden center and use it according to directions.
If we haven’t hit on the answer yet, take some more shots including underneath of the leaves and give us some more information about the history of the plant and we’ll take it from there!
Leave A Comment