Inkberrry – A Native Evergreen Shrub

Ilex glabra, commonly called inkberry or gallberry holly, is an evergreen shrub native to the eastern and south-central U.S., including the coastal region of Virginia and its southeastern counties. It is not native to the Piedmont Virginia region. It is a member of the botanical family Aquifoliaceae (holly). Inkberry is often used as a native evergreen alternative to boxwood and to other nonnative evergreens, such as Chinese, Japanese, and European hollies, and the more compact cultivars of Chinese juniper. A 1991 article in Arnoldia by Dirr and Alexander describes the appeal of Ilex glabra:

As part of the native plant movement, and with its superior adaptability, Ilex glabra is a natural for increased landscape use. Recent emphasis on wetland mitigation is another plus for the species.

ADAPTABILITY

Although commonly found in moist to wet soils, this highly adaptable shrub does well in home landscapes. It can thrive in conditions ranging from full sun to moderate shade; from wet to dry sites; and from sandy soils to clay. It likes an acid to neutral soil with a pH range of 3.5-6.0; it has good salt tolerance. When the earth is too alkaline, inkberry is prone to chlorosis, or a yellowing of the foliage. The straight species is generally hardy in USDA Hardiness Zones 5-10.

CHARACTERISTICS

Inkberry has an upright, rounded habitat developing multiple trunks. Stems arise from heavy, tuberous rhizomes which often produce suckering. Oval, alternate leaves are a shiny dark green on top, with undersides that are duller and lighter. Leaves have a smooth edge except near the top where there are several teeth. The shrub tends to become more open and leggier as it grows to a mature height of 5-10’ and a width of 5-8’. Many consider this legginess to be one of the species’ drawbacks, and cultivars have been developed to improve fullness. These cultivars will be discussed in a later section. Inkberry may be propagated from stem and root cuttings, or from suckers.

BERRY PRODUCTION

Flowers are dioecious, meaning that individual flowers are either male or female, and only one sex is found on each bush. Both male and female hollies are required if berries are desired. The flowers are not self-fertile and are pollinated by bees. If pollination occurs between male and female plants, flowers are followed by pea-sized, jet black, berry-like drupes which mature in early fall. Female shrubs are common in nurseries, but it is difficult to find male cultivars, or male inkberry straight species.

Kim Eierman of EcoBeneficial discussed the problem of finding male inkberry cultivars in the nursery trade:

Named cultivars, like ‘Shamrock,’ ‘Nordic,’ ‘Nigra,’ ‘Densa’, ‘Compacta,’ ‘Cape Cod,’ etc., are one sex – and all of those cultivars are female.  The only confirmed male cultivar that I and the Holly Society of America are aware of is ‘Pretty Boy.’  I have seen that cultivar offered for sale during one season at one nursery (which is no longer selling it).  ‘Nordic’, often listed as a male, is actually a female. 

In her article, “Looking For Mr. Goodbar—The Quest to Find Male Native Plants,” Eierman points out that this is a problem for many native species, and provides a list of other dioecious shrubs and trees.

ECO BENEFITS

Although the berries are not considered ornamentally impressive, they are a good food source for wildlife. Birds that are attracted to the berries include bobwhite quail, wild turkey, and many songbirds such as bluebirds, brown thrashers, and hermit thrashers. Opossums, racoons, and coyotes will also eat the berries when food is scarce. Deer sometime feed on the foliage; it is not attractive to rabbits. Inkberry also provides good winter cover for wildlife.

Inkberry is a larval host plant for the Henry’s elfin butterfly (Callophrys henrici) which appears from February to May and has one flight. The adult Henry’s elfin butterfly feeds on the nectar from inkberry flowers. Inkberry is also larval host to Celastrina idella, the holly azure butterfly. Other adult butterflies and bees are attracted to the blossoms as well. The specialized native bee, Colletes banksi, forages solely on holly flowers.

Gallberry honey is a highly rated honey produced from bees feeding on inkberry flowers. This honey is locally produced in certain parts of the southeastern U.S. Beekeepers release bees from late April to early June to coincide with inkberry flowering time.

PRUNING

Most evergreen pruning, which includes inkberry, is done for corrective reasons, so seasonal timing is usually not as important as it is for deciduous species. Pruning during dormancy, i.e., late winter/early spring (February-March) is the most common practice and will result in a vigorous burst of spring growth. If you don’t have male inkberries, or you are not concerned about berry production, this is a good pruning schedule.

If you are interested in berry production, however, there are other pruning options to consider. Inkberry blooms on old wood, meaning flower buds for next year’s blooms form during the current growing season. The buds are carried over through winter on last year’s growth, the old wood. If you prune male shrubs in late winter/early spring, you’ll cut off at least some of the flowers needed for pollination. In this case, you may want to prune male shrubs right after flower bloom. For female shrubs, as flowers finish blooming, those that were pollinated set fruit; pruning in midsummer will sacrifice some berry production. If you prune in late winter/early spring, you’ll cut off flower buds. Choose your schedule knowing that pruning in either period will reduce berry production. It is likely that at some point pruning will be beneficial, and you’ll need to make a choice.

Maintenance pruning is usually needed to address legginess in the species. As the plant matures and becomes thin, remove up to one-third of the branches to their points of origin in early spring. Deep pruning means taking a mature shrub down to crown level for a total makeover. If an inkberry needs rejuvenation, i.e., it’s spindly and has lost lower stems and foliage, cut it down to 1-1.5’ high in early spring when it is poised to push out new growth. This will give time for a strong flush of growth to harden off before winter.

CULTIVARS

The following is a list of inkberry cultivars, along with brief information on how the original cultivar stock was developed. The information on cultivar origins is from a 1991 article by Michael Dirr and John H. Alexander III published in Arnoldia. It is interesting to note how long these cultivars have been in the trade. Although they haven’t “solved” the legginess characteristic of the species, some offer a denser form, a somewhat improved retention of lower branches and foliage, and more compact forms better suited to small spaces. Two white-berried forms are native to the Coastal Region of the eastern U.S.: Ilex glabra forma leucocarpa, and Ilex glabra f. leucocarpa ‘Ivory Queen’. Although interesting, they don’t seem to be commonly available in the trade.

‘Compacta’

Selected in 1937 from a block of seedlings planted from seed collected in the New Jersey pine barrens. This compact plant grows 3-4’ tall and 4-6’ wide in a tight oval to rounded habit. As noted by Dirr and Alexander: “Like the species, it becomes leggy at the base and loses a portion of the lower foliage, but if pruned in a timely and artistic manner, it will remain a handsome plant.” Thick dark green leaves fade to olive green in winter. Hardy in USDA zones 4-9.

‘Densa’

This cultivar was selected from a batch of 500 seedlings in 1938 for its oval to round, uniform outline with upright branches and leathery dark-green leaves. This mid-sized shrub grows 4-6’ tall and wide.  Its leaves are described as wider and rounder than those of ‘Shamrock’. Hardy in USDA zones 4-9.

‘Nigra’

This larger cultivar grows 6-10’ tall and wide. Foliage color is a dark green. Older plants may be renewed by heavy pruning as lower branches lose foliage with time. Hardy in USDA zones 5-9.

 

 

 

 

Ilex glabra ‘Chamzin’ NORDIC

Selected out of 2,000 inkberry seedlings growing in a nursery field, it was noticed for its distinct broad pyramidal growth habit and dark green foliage. Its leaves are somewhat larger than the species. It grows 3-4’ tall and wide and is less likely to sucker. Hardy in USDA zones 3-9.

‘Shamrock’

This cultivar was selected in 1977 from a block of approximately five hundred seedlings for its compact habit and bright, glistening new green foliage that overlays the previous year’s mature dark green foliage. It grows to 3-5’ tall and wide, with upright branches. Its rounded, compact habit may become leggy with age. Hardy in USDA zones 4-9.

DWARF CULTIVARS

GEM BOX® is about 2-3’ tall and wide with a round habit and petite foliage. New growth in spring has a reddish tip. Hardy in USDA zones 5-9.

STRONG BOX® is about 2-3’ tall and wide with leaves that are a little bit broader than GEM BOX®. Hardy in USDA zones 5-9.

PLANT VIRGINIA NATIVES CAMPAIGN

This campaign is an effort to help Virginia gardeners identify plants native to their area. Refer to the article in this month’s newsletter, “Coming to a Garden Center Near You,” for more information. For inclusion on the list of recommended plants, cultivars of straight species have been vetted to ensure they are ecologically viable, meaning their leaves and flowers contribute to the food web and do not negatively alter insect behavior. The inkberry cultivars native to southeastern counties of Virginia are on the list of recommended plants: ‘Shamrock’, ‘Compacta’, ‘Densa’, and ‘Nigra’.

PESTS AND DISEASES

In general, inkberry is a disease- and pest-resistant plant. It is susceptible to chlorosis (yellowing of leaves) in high pH (alkaline) soils. Leaf spot is an occasional problem. Spider mites may appear, especially in dry conditions. This shrub may also be prone to Phytophthora root rot; look for resistant alternative species if this disease is in your area. Branches are prone to breakage under snow or ice load. It has a high flammability rating.

HOW TO USE IN THE LANDSCAPE

In foundation plantings, inkberry is often used as an evergreen substitute for boxwood, especially in areas where boxwood blight is prevalent, or for other nonnative evergreen shrubs. Remove suckers from inkberry if spreading is not desired. Plant groundcovers or low perennials in front of inkberry to add fullness and to hide sparsely leaved lower stems. When used as a hedge, inkberry’s suckering tendency can be used to advantage. You can also trim the hedge to a desired height. Inkberry is a good addition to native pollinator corridors, wet areas of the landscape, and naturalized areas. Dwarf varieties, such as GEM BOX® and STRONG BOX®, can be used in containers if they are given sufficient water.

SUMMARY

Although naturally found in moist to wet areas, inkberry is known for its adaptability to different levels of moisture and sunlight, and soil type. Although current native plant enthusiasts may view inkberry as a “new” native plant choice, it has been in the trade for a considerable amount of time. Inkberry is a good native plant alternative to boxwood, especially in areas where boxwood blight is prevalent, and to other nonnative evergreen species. Cultivars have been developed to address the tendency of the species to thin out and become leggier as it matures. Many of these cultivars will still benefit from maintenance pruning to promote fullness. For fruiting, male inkberries are required; unfortunately finding them in the trade is a challenge. Inkberry is an attractive, adaptable, eco beneficial native choice that deserves strong consideration as a landscape addition.

 

SOURCES

Feature Photo: Ilex glabra ‘Shamrock’, Courtesy of Missouri Botanical Garden

“Ilex glabra – The Inkberry Holly,” Dirr and Alexander, Arnoldia (1991)

“How Do I Find a Mate for My Inkberry?” Kim Eierman, EcoBeneficial!

“Looking for Mr. Goodbar – The Quest to Find Male Native Plants,” Kim Eierman, EcoBeneficial!

“Native Plant Profile: Ilex glabra,” Maryland Department of Natural Resources

“Ilex glabra,” Floridata

“Ilex glabra,” NC State Extension

“Ilex glabra,” Missouri Botanical Garden Plant Finder

“Ilex glabra ‘Compacta’, Missouri Botanical Garden Plant Finder

“Ilex glabra ‘Chamzin’ NORDIC,” Missouri Botanical Garden Plant Finder

“Ilex glabra ‘Shamrock’, Missouri Botanical Garden Plant Finder

“Ilex glabra f. leucocarpa,” The Dawes Arboretum

“Ilex glabra f. leucocarpa ‘Ivory Queen’, The Dawes Arboretum

“Native Bees: These Bees Plastic-Wrap Their Brood Cells,” Dickinson County Conservation Board, IA

“Celastrina idella,” Butterflies and Moths of North America

“Callophrys henrici,” Butterflies and Moths of North America

“American Holly- More Than Just a Holiday Decoration,” The Garden Shed

“What do var., ssp., subsp., forma, and f. mean?  Capturing California Flowers

“Phytophthora Root Rot of Trees and Shrubs,” Missouri Botanical Garden

“Boxwood Blight Alert,” The Garden Shed