Many Northern gardeners, myself included, often feel cheated by the limited number of plants we can grow as compared to our southern gardening friends. This is especially evident by our limited palette of hardy broadleaf evergreens. Lustrous dark green hollies and southern magnolias, beautiful large-leafed rhododendrons and fragrant evergreen gardenias -- all a bit of a stretch for us!
There are however, a few nice broadleaf evergreens we can grow quite well. One such plant that is often over-looked is boxwood (Buxus sp.). Boxwood or box as the English call it, is a wonderful small shrub that graces the garden with lustrous green foliage throughout the year. The majority of boxwood species are fairly tender and not hardy in south central Wisconsin, but there are a few suited to our growing conditions with proper siting.
Boxwood, like other woody plants, help make up the "bones" of the garden. They add structure to a mixed border when combined with perennials, annuals and other shrubs and trees and are especially welcome during the winter, bringing a little greenery to an otherwise drab landscape.
Box are also the hedge plant of choice in formal gardens. In fact they have been used for hedging and making topiary forms since ancient times, dating back to 4000 B.C. Since its early cultivation, box has been clipped into every conceivable shape, from triangles and squares, to birds and teddy bears and everything in between! If left unpruned, or lightly pruned, most assume a pleasant feathery globe shape.
The Korean box (Buxus microphylla var. koreana) is the hardiest species of all the boxwood and its' popular cultivar 'Winter Green' is especially tough and attractive. This beauty is clothed in small, but dense, light green foliage. Winter green box, as its name suggests, retains its good green leaf color during the dormant season, unlike the ordinary species which turns light brown.
This selection blooms as early as April in our area, but like all box, the fragrant flowers are rather inconspicuous. ‘Winter Green’ is a compact grower reaching a height and width of 3-5', but is easily sheared to a smaller stature if preferred.
Three more boxwood cultivars that have been proven performers in south central Wisconsin are ‘Green Gem’, 'Green Mound' and 'Green Velvet'. These recent selections are the hardiest members of the "Sheridan Hybrid" series, developed by Sheridan Nurseries in Ontario, Canada. They combine the hardiness and compact habit of the Korean box with the rich, dark green, glossy foliage of the common box (Buxus sempervirens).
Green gem boxwood (Buxus x 'Green Gem') is a slow-growing dwarf plant that forms a tight ball measuring about 2' x 2'. It has very dark green foliage throughout the year. This small cultivar makes an excellent short, formal hedge when planted closely and requires very little shearing to maintain its shape.
Green mound boxwood (Buxus x ‘Green Mound’) is very similar to ‘Green Gem’, but has a bit finer-textured leaf and is slightly bigger in stature reaching an ultimate height and width of 3 to 3 1/2 feet.
Green velvet boxwood (Buxus x 'Green Velvet') is also similar to ‘Green Gem’, but grows up to 3 to 3 1/2 feet tall and wide.
Last, but not least, Chicagoland Greenª boxwood (Buxus x ‘Glencoe’), a recent introduction from northern Illinois, has proved to be an excellent performer as far north as Minneapolis. This broadly mounded cultivar sports medium green foliage year-round and is a rather quick grower. Twelve year old plants at the Chicago Botanic Garden, where the plant was discovered, measure 3’ tall and 5’ wide.
If you decide to give one of these boxwood a try, there are some important cultural considerations to keep in mind. Boxwoods perform best if sheltered from winter sun and wind -- a partly sunny or shady location, possibly in the understory of a large tree or on the east or north side of a building or fence. If you are unsure of your site, you may want to give ‘Wintergreen’ a try first, since it is the hardiest of the group -- if it grows well try one of the other four.
Box are very insect and disease resistant plants and grow well in average soils, neither excessively dry nor wet. They are not particular about pH and do quite well in our alkaline soils at Olbrich. It is important to keep the shallow root system cool and moist, so as with most other landscape plants, boxwood benefit from a few inches of organic mulch.
The first winter is probably the most critical to the health of a newly planted box. Until the plants develop an extensive root system the foliage is subject to winter burn, so it is always a good idea to water the plants well in late fall and again, make sure the roots are mulched to conserve moisture.
Four of the five above mentioned boxwood cultivars can be seen at Olbrich Botanical Gardens. Established plants of ‘Wintergreen’ are growing in the Rock Garden, ‘Green Mound’ and ‘Green Velvet’ are in the Herb Garden and ‘Chicagoland Green’ is planted at the west entrance to the Sunken Garden.
I encourage you to give this excellent landscape plant a try -- you won’t be disappointed!