American holly is normally planted from potted nursery specimens in the spring or early fall. It has a medium growth rate, adding 12 to 24 inches per year until reaching its mature size of 30 feet or more. If planting for a screen or in groups, space the plants about 5 feet apart in a prepared hole two or three times larger than the container root ball. Backfill the hole with soil blended with organic material plus an acidifying amendment, if needed. Keep the plant moist until established.
Light
American holly will grow nicely in most full sun to part shade locations. In hot climates, plants will do best if they get some afternoon shade.
Soil
Give this plant a well-drained, acidic soil. If necessary, amend the soil to acidify it, or be prepared to feed it regularly with an acidifying fertilizer.
Water
American holly needs to be kept moist while it getting established, but after the first year or so, watering once a week (about 1 inch) is sufficient. This plant has a good tolerance for occasional drought.
Temperature and Humidity
American holly generally does well throughout the temperature range of its hardiness zone, 5 to 9.
Fertilizer
Early each spring, American holly will appreciate an application of an acidifying fertilizer.
American Holly Varieties
There are hundreds of different cultivars of American holly; the pure species plant is almost never planted. Holly cultivars are normally sold as either female (berry-producing) or male plants (necessary to pollinate the females). These are some popular varieties:
‘Cobalt’ is a male cultivar with good cold hardiness (down to minus 25 degrees Fahrenheit).‘Jersey Knight’ is one of the most popular male cultivars, growing to 7 to 10 feet over 10 years.‘Miss Courtney’ is by some standards considered the best female cultivar. It grows 20 to 30 feet and is cold hardy down to minus 20 degrees Fahrenheit.‘Morgan Gold’ is a yellow-berried female cultivar growing to 25 feet.‘Maryland Dwarf’ is a diminutive, 2-foot-tall plant with few berries.‘Cardinal Hedge’ is a dwarf cultivar, growing to only about 4 feet, excellent for foundations and small hedges.
In order to produce berries, female hollies will require a male plant within 30 to 40 feet. It is fine to plant a single male to pollinate all your female hollies.
Landscape Uses
In landscaping, American holly can be used as a specimen plant, in groups, or in foundation plantings, where they add good winter color and attract birds with their colorful berries. Holly is perhaps most commonly used to add visual interest to color-starved landscapes in winter. And, of course, holly is prized for Christmas decorations, both indoors and outdoors. Several bird species are attracted to holly shrubs, including thrushes and blackbirds. According to the USDA Forest Service, holly berries are also eaten in winter by wild turkeys, cedar waxwings, mourning doves, goldfinches, bobwhites, and cardinals.
Pruning
American holly does not require pruning, though you can do so to improve its shape or to remove dead or diseased branches. Pruning is best done in winter, while the plant is dormant. Prune in a manner to work with the natural shape of the tree, rather than to force it into an artificial shape. The leaves are sharp, so wear long sleeves when trimming. Start by pruning any dead or damaged branches down to a point several inches below the damage. Next, prune away some of the remaining branches to open the plant up and improve its shape. Make sure to keep the bottom of the plant rather full so lower foliage is not shaded by upper branches. A holly plant can be pruned severely all the way to the ground if it gets overgrown, but this should be done over the course of three years or so to avoid serious shock to the plant. Remove about one-third of the full-length branches each year. Such a plant then responds with lots of vigorous new growth.
Propagating American Holly
Creating new holly plants by rooting some stem cuttings is fairly easy to do, but it takes quite a lot of time. In late summer, cut 6-inch pieces of stem from the tips of new growth branches. Strip away all but the top three or four leaves. Plant the cuttings in a container filled with a mixture of sand and peat moss. Thoroughly moisten the potting mix, then place it in a sealed plastic bag. Set the pot in a warm location (60 to 70 degrees Fahrenheit) and check it weekly, watering when necessary. In four to six weeks you should see some new growth beginning, and at this time you can remove the plastic bag and set the pot in a sunny window. After a few months, you can transplant each growing holly sapling into a large container filled with ordinary peat-based potting mix. Continue to grow the plant in a sunny window until spring, when you can move the potted saplings outdoor to continue growing—or plant them in the landscape if they are big enough.
Common Pests and Diseases
Holly plants can be susceptible to many insect problems, such as leaf miners, spider mites, whitefly, and scale. Horticultural oils will generally help with most pests, but systemic insecticide may be necessary if leaf miners become too disfiguring. These plants are also prone to fungal rots, which will usually require that the plant be removed. These are more likely to occur in dense, boggy planting locations. The fungus can persist in the soil for many years, so it’s usually best to change to another plant altogether when fungal disease appears. Holly plants can also be victims of leaf drop and sun scorch in very hot conditions. If the leaves turn yellow, it may be due to soil that is too alkaline.
