American holly (Ilex opaca) is a small to medium-size tree with a dense, pyramidal growth habit. Plants are prized for their glossy, evergreen foliage and bright red fruit. Sprigs of American holly are often used in wreaths, centerpieces, and other Christmas decorations. Unfortunately, American holly doesn't perform well in Iowa. However, winterberry and several Meserve hybrid hollies can be successfully grown in the state.
The flowers of all holly species are small and inconspicuous. Hollies are dioecious. Dioecious plant species produce male and female flowers on separate plants. Only female holly plants produce attractive fruit. However, a male holly plant is required for pollination and fruit set.
Winterberry (Ilex verticillata) is native to much of the eastern United States, including parts of northeast Iowa. While most holly species are evergreen, winterberry loses its leaves in the fall. Plants commonly grow 6 to 10 feet tall. The fruit on female plants turn bright red in fall and persist into winter. (The fruit are eventually devoured by birds.)
Gardeners can choose from several female varieties noted for their excellent fruit display. Red-fruited varieties include 'Sparkleberry,' 'Winter Red,' 'Shaver,' 'Afterglow,' and 'Red Sprite.' Other attractive varieties include 'Aurantiaca' (orange fruit) and 'Winter Gold' (pinkish orange fruit).
When planting hollies, a male variety must be planted in the same general area as the female hollies for pollination and fruit set. One male plant is adequate for several female plants. 'Jim Dandy' is a suitable male pollinator for 'Shaver,' 'Afterglow,' 'Red Sprite,' and 'Aurantiaca.' Southern Gentleman' is a good pollinator for 'Winter Red,' 'Winter Gold,' and 'Sparkleberry.'
Winterberry performs best in moist, acidic soils with a soil pH of 5.0 to 6.0. Plants can be grown in partial shade to full sun. Best fruiting occurs in those areas that receive at least 6 hours of direct sun. In alkaline soils, winterberry leaves may be yellow-green. This condition is referred to as chlorosis and is due to a lack of chlorophyll in the leaf tissue. Chlorosis can be prevented by adding large amounts of Canadian sphagnum peat to the soil when planting. Incorporating Canadian sphagnum peat into the soil helps lower the soil pH.
Several hybrid evergreen hollies, collectively known as Meserve hybrid hollies (Ilex x meserveae), can also be grown in Iowa. 'Blue Prince,' 'Blue Princess,' 'Blue Boy,' and 'Blue Girl' have dark, bluish green foliage and are often referred to as blue hollies. The female varieties produce attractive red fruit. Other Meserve hybrids include China Boy®, China Girl®, Castle Spire™ (female), and Castle Wall™ (male).
Meserve hollies are variable in height. Most varieties grow 5 to 10 feet tall. They are hardy to -20 degrees Fahrenheit (USDA Hardiness Zone 5). In Iowa, Meserve hollies perform best in the southern half of the state. Meserve hollies are susceptible to desiccation injury from the sun and dry winds in winter. When selecting a planting site, choose a protected site, such as on the east side of a building.