Rhododendrons are evergreen shrubs used extensively as ornamental or landscape plants in the United States. Once established, they require little care. In the first few years, however, they require winter protection to get through, especially in colder regions. Even older plants need this protection at times if they reside in an unprotected area. Knowledge of how to best harden your plants to the cold will keep them healthy and attractive.
Stop fertilizing in July. Any extra added nutrients after this point will encourage new shoots, which are highly susceptible to frost damage. If these shoots die, it opens the bush up to disease.
Reduce watering in September, allowing the bush to dry into October. This will harden it off for the winter. Rhododendrons, however, as they are evergreens, need a store of water before the cold sets in. Provide this for your plant by giving it a good drink around Thanksgiving.
Place a 2- to 4-inch layer of mulch around the base of the plant after the first hard frost. This will protect the shrub's shallow roots against heavy temperature fluctuations. Keep the mulch from directly touching any stems of the plant.
Cover the bush with a sheet or burlap staked to the ground as the cold weather sets. This will protect it from the sun and harsh winds.