The lovely rose of Sharon (Hibiscus syriacus) is a summer-blooming ornamental shrub that produces showy, colorful flowers from July to September. Its elegant vase-like habit and palmate gray-green leaves make the shrub a beautiful addition to the traditional romantic garden. When young, the rose of Sharon develops as a beautiful compact bush. The shrub grows rapidly, however, and may overpower a foundation garden bed. Before planting this shrub near your home's foundation, consider a few facts.
The rose of Sharon is a rapidly growing shrub, extending to an average height of 8 to 10 feet in a few years. This exceptional height is too tall for a foundation plant, as the shrub will overpower the other plants in the bed and conceal the house windows and architectural details. Rose of Sharon is not too picky about soil quality, but it does prefer the alkaline soil commonly created by the limestone mortars of house foundations. The plant also propagates quickly, rapidly populating the foundation landscaping with numerous suckers.
Damage to Foundation
Technically, any shrub can damage a house's foundation. Curious roots seeking more space, water and nutrients may wheedle their way into tiny weaknesses in the foundation wall. The rose of Sharon is a fast-growing and profligate plant, rapidly stretching out its roots to claim more territory for its own branches and its suckering offspring. Tiny underground ventricles may eventually poke into and permeate the mortar of older stone foundations pocked by years of rain and frost heave. When given the choice, however, the plant is more likely to extend into the adjoining soil than interfere with the foundation wall. For newer concrete or cinder block foundations, damage from rose of Sharon is unlikely.
Water is more hazardous to the foundation than burrowing roots. When fully established in close proximity to the house foundation, the rose of Sharon provides thick overgrowth, shading the foundation and retaining moisture below the ground. Mildew, mold and fungus may latch on to the foundation, eroding the surface and allowing water to seep into small cracks. The water will freeze during the winter season, enlarging the cracks. In severe cases, the cracks may allow water to seep into the depths of the foundation walls, causing more damage. Larger rose of Sharon shrubs may also interfere with rainwater dispersal, clogging gutters and inhibiting proper roof drainage.
While the rose of Sharon in most cases will not damage a house's foundation, the threat of foundational damage remains because of the shrub's speedy root and branch growth, fertile reproduction and towering height. Rose of Sharon is best planted in a shrub border or in a mass planting at least 5 away from the house foundation, where the plant can broaden its branches unhampered. If the shrub is currently growing near a foundation, the dangers are slight, yet you would be wise to control its fast growth with annual pruning. Pruning allows rose of Sharon better air circulation and staves off its wild, suckering habits.