We have several hardy hibiscus. This is the third summer for them. They begin blooming in July with large (6-8 inch) flowers. But by mid August each of the flower buds dries up and turns brown before opening. The leaves sometimes have holes in them. I have found small green caterpillars, so I usually spray the plants with Diazinine once a week. We live in the Texas Panhandle. The highs each day is 80-90 and the lows are in the 60s. The plants get 6 hours sun. I have tried watering both every other day and every fourth day to see if that helps. We are using a red mulch with Preen weed killer in it. Do you know what is keeping the flowers from opening?
Certified GKH Gardening Expert
They normally drop flowers during hot weather due to lack of water. While you are watering, it may not be penetrating the mulch to the roots below. Mulch can actually repel water sometimes, so check the soil below to make sure that the water did actually get through. Water deeply as well. Fertilizing while they are in bloom can also cause the buds to fall off. So, avoid that as well.