If you’re gardening in U.S. Department of Agriculture plant hardiness zones 4 through 8 and scratching your head over those bare shady spaces, consider mapleleaf viburnums (Viburnum acerifolium). One of these deciduous 4- to 6-foot high shrubs spreads 4 feet. In its natural habitat, the forest understory, and in landscapes that mimic this, it quickly spreads by suckers to form a large colony. Mapleleaf viburnum performs best in well-drained soil.
How Does Your Soil Drain?
To save your mapleleaf viburnum unnecessary grief, test your soil drainage in the fall before planting in the spring. After digging and filling a 1-foot deep hole with water and letting it drain, refill and measure and record the water’s depth. After 15 minutes, measure it again and subtract the result from your first measurement. Multiply by 4 to determine how many inches of water drain from the soil in an hour. If the answer is less than 1 or more than 6 inches, your soil needs attention.
Soil Drains Like Molasses
Phytophthora fungi, which thrives in poorly draining soil, may attack your viburnum’s roots, crown or collar. Symptoms of infection include stunted, wilting and prematurely dropping foliage, dying twigs and branches, or oozing, cankered bark. Severely infected viburnums die. Excessive water also squeezes the oxygen out of the soil and slowly suffocates the roots. An affected viburnum has dying twigs with desiccated, wilted yellow leaves and dying twigs. Too much water, in other words, is as likely to kill your viburnum as too little.
Soil Drains Like Your Child's Favorite Drink
A viburnum planted where water drains too quickly for its roots to absorb ends up both thirsty and nutrient-deprived. Its wilting leaves, crisp along the margins, fade to yellow or brown or assume their striking fall color weeks ahead of schedule. This viburnum produces fewer flowers, and in an attempt to conserve energy, it may stop growing completely. Fortunately, the same remedy fixes slowly or rapidly draining soils. Once you've applied it, plant your viburnum with confidence.
Recipe for Perfectly Draining Soil
Improving your soil’s drainage is a simple matter of altering the size of its particles. The desirable 1- to 6-inch-per-hour drainage rate belongs to loam's medium-sized, nutrient-dense particles. To achieve this, amend your dry soil with organic matter, such as compost or peat moss. Then rototill it to a 6- to 8-inch depth, cover it with a 6 to 8-inch layer of your amendment, and mix until the soil and amendment are indistinguishable from one another. This effort yields 12 to 16 inches of a well-drained, half-soil, half-amendment growing medium. With proper care, a viburnum planted in it rewards you with abundant clusters of creamy blooms, bird-attracting berries and maplelike foliage of exceptional pink to purple fall color.
- Manual of Woody Landscape Plants, Fifth Edition; Michael A. Dirr
- Missouri Botanical Garden: Viburnum Acerifloium
- University of California Statewide Integrated Pest Management Program: Viburnum
- University of California Statewide Integrated Pest Management Program: Collar, Foot, Root and Crown Rots -- Phytophthora Spp.
- 2001 Sunset Western Garden Book; Kathleen N. Brenzel, Editor
- Missouri Botanical Garden: Drought and Water Stress
- Utah State University Cooperative Extension: Preparing Garden Soil