Background:

During the holidays, holly branches add a bright, dramatic touch to wreaths. Hollies can add that same drama to the landscape. Hollies (genus Ilex) with their beautiful evergreen foliage and bright berries make good accent plants, hedges and also add great winter color. They are fairly easy to grow and have few pests or other problems. Hollies do have a reputation for slow growth, but new hybrids have increased the speed of growth; Ilex meserveae can become a good-size shrub in just a few years.

All members of the Ilex family are not evergreen shrubs. The American Holly (Ilex opaca) grows to 50 feet. There are dwarf forms that can be used as low maintenance hedges as well as deciduous forms such as Ilex verticillata

Cultural Conditions:

•  For the fullest, most compact growth and best berry production, hollies need full sun, although they will tolerate shade. They thrive in slightly acidic soil with lots of organic matter. The soil needs to be well-drained, as hollies do not like overly moist soil. Regular watering, however, is needed to keep the plants looking their best. Several inches of mulch will help preserve moisture in the soil.

• A dose of acid-based fertilizer in late fall will give the plant a good start on the growing season. Adding a good layer of compost helps fertilize the plant and adds organic matter to the soil.

• Hollies respond well to pruning. Greens can be cut for the holidays without harming the plant. Holly can be pinched back to promote branching and new leaf production for a fuller plant.

Problems:

•  Chlorosis, a yellowing of the leaves, can be a problem if the soil pH is too high or if the plant is not receiving enough nitrogen. If the leaves begin to yellow in the summer, an application of a 10-5-5 fertilizer should help. If the problem is persistent, check the pH of the soil.

• Holly foliage can be damaged by wind and dry conditions, especially if the plant is in an exposed site. Drying out can be a significant problem for young plants.

•  Insects which can infest Ilex include scales, bud moths, red mites and leaf miners. Damage inflicted by these insects is usually minor. A careful spray with an insecticidal soap should be sufficient to control any insect infestation; a routine spraying regimen is not recommended.

Holly varieties for the landscape:

The English holly, Ilex aquifolium, is the "typical" holly plant. I. aquifolium is very sensitive to drying out and needs to have its roots mulched to keep them moist. There are several variegated forms which make excellent specimen plants or backgrounds for a perennial border.

The hybrid 'Nellie R. Stevens' is similar in appearance to the English holly but has fewer problems. 'Nellie' is a fast-growing cross between the English and Chinese holly. This cultivar has excellent dark green foliage and large, red berries and will grow into a beautiful specimen tree.

The Meserve hollies, commonly referred to as the blue hollies, are some of the easiest to grow. Very hardy and reliable for setting berries, they make a dramatic addition to the landscape. The foliage is very dark green with a blue cast. 'Blue Stallion' and 'Blue Princess' make an excellent hedge. Other Meserve hybrids are 'China Boy' and 'China Girl'. The foliage of these hybrids is a lighter green and has excellent berry production.

Different forms of hollies:

The Japanese holly, Ilex crenata, is a good substitute for boxwood. Very similar in appearance to boxwood, the Japenese holly is very hardy and grows more quickly than boxwood. The leaves are evergreen, but not stiff like traditional hollies, and have a soft gray cast. The berries are blue and not highly conspicuous. Dwarf varieties such as 'Helleri' will produce a nicely shaped hedge with little pruning.

Ilex glabra, a native holly, is now being used in roadside plantings and makes an excellent evergreen hedge. This holly is extremely hardy--it grows in any soil, in full sun or partial shade and is pest and disease resistant. The foliage is persistent during the winter and has a rich blue-green cast. Ilex glabra's blue berries attract birds.

Deciduous hollies can thrive in the landscape as well. Winterberry (Ilex verticillata) is a native deciduous holly. The summer foliage of winterberry is not as dramatic as the evergreen, but the berries that persist during the winter are very attractive. 'Sparkleberry' is an attractive hybrid of winterberry with sparkling red berries highlighted in the winter landscape. While the dwarf form 'Sprite' is a much smaller bush, its large red berries cover the bush in the winter. Both of these hybrid forms are compact and work well in smaller yards.

For best berry production:

• Hollies are dioecious, having separate male and female plants. If you want berries you need to plant one male for every 5-10 females.

• Your plants also need to be compatible. It is important to choose the same variety of male and female holly so that they bloom at the same time, which allows for the exchange of pollen.

• Don't over fertilize! Flowering and therefore berry production is inhibited, if the nitrogen level in the soil is too high.

Note: Holly leaves and berries are toxic and should not be ingested

By Cheryl Cadwell, URI Master Gardener