Leaves of Hoya are Wrinkling

The leaves of my Hindu rope plant (Hoya carnosa ‘Crispa') are wrinkling.

Over or under watering can cause the symptoms you describe. Most gardeners tend to over water their plants. Hoyas are succulent plants that do best in full sun and dry soil with warm summer and cool winter temperatures. Water the soil thoroughly. Pour off the excess so the plant does not sit in a saucer full of water. Allow the soil to dry slightly between watering. Water just before the potting mix dries. Excessively dry potting mix forms a hard block that is difficult to rewet. You may need to water your plants as seldom as once a month. The more light and warmer the temperature the more frequently you need to water. Adjust the watering schedule to fit the growing conditions and you should see an improvement.