You have probably noticed, or have, Cotoneaster hedges that have large dead patches or are dead altogether. It is the work of the oyster shell scale insect. The tell tale sign are the small raised squiggly blisters that are all over the branches, below.
These tiny insects live under their hard scale most of the year so are difficult to control. In late May and early June the eggs hatch and the insect becomes a "crawler" this is when Insecticidal Soap can be used on the plants. Insecticidal Soap is the least toxic option for the environment and for humans and washes off with rain or water, follow the package directions. The only other option is to cut the hedge down, if not too damaged, and it will grow back up again from the roots. The other bad news is that I have noticed this pest on Dogwood, Apple, and Crab apple in our area, the literature lists 130 trees and shrubs that are vulnerable so stay on guard and inspect regularly! If caught early plants can be rescued but if left alone can completely kill specimens.
This got me thinking about other shrubs we could use as hedging, there is always danger in monoculture that a disease or pest could wipe out one species, it's important to have biological diversity in our environment so we aren't left devastated later on. Below are some candidates for hedging that I gathered just from walking my neighbourhood, I haven't necessarily seen these as hedges but they are worth a try.
Barberry, were banned on the prairies since the early 1900's for giving a disease to wheat, in the early 2000's this problem was overcome and Barberry is welcome once again. This plant was once called Postmans Hedge because it would block even the postman from crossing your lawn because of the numerous thorns. There are several varieties available Rose Glow is probably the tallest. These plants are drought tolerant and have attractive red/burgundy leaves. I think they have great potential as hedge material except watch out for the very prickly stems, they really hurt!
Honeysuckle, the variety I'm thinking of is Lonicera tatarica, which may be hard to find as it's pretty old fashioned now. These shrubs grow wild in my local dog park and were used extensively in my mid century neighbourhood. They take easily to hard pruning and don't grow continually through the season like many shrubs. Honeysuckle blooms in pink, white, and yellow and has thin skinned red berries. They can grow almost 20 feet tall but could be controlled into a hedge very easily, also very hardy hailing from Siberia, drought tolerant and early to leaf out in the spring.
Mock Orange, Philadelphus, Blizzard is the taller variety, up to 7 feet. With it's small leaves and compact growth habit this would be perfect for a hedge with the bonus of orange smelling white flowers. Hardy drought tolerant, easy to grow, a longtime prairie favourite.
Saskatoon, these berry bushes grow wild almost everywhere there is a ravine in Calgary. Also available as nursery stock. The compact habit would easily lend itself to hedging just make sure you get the height you want. The bonuses would be completely hardy, spring flowers, summer berries and attractive fall colour.
Snowberry, Symphoricarpos albus, also grows wild in our area and has attractive leaves and white berries in the fall, also available in retail, these shrubs grow about 3 feet tall. These plants sucker easily and can fill in a small area quickly. The only real drawback is the berries turn black after freezing weather. I think they would make a low and informal hedge.
Upright Juniper, probably the best candidates for hedging would be the varieties, Medora, Moonglow and Wichita Blue which can all grow over 20 feet tall. I would think with light trimming these shrubs would make a dense and evergreen barrier. Hardy and drought tolerant Juniper is easily grown in Calgary. The only drawback for making a hedge would be the cost, individual junipers usually sell for over $100.
False Spirea, Sorbaria sorbifolia, is an attractive plant that grows to about 6 feet tall and wide, these plants also have a large white feathery flower head resembling astilbe. These plants spread aggressively and this should be considered wisely. I have seen this as a sort of informal hedge across the prairies and would be great for a large area or space that is bordered by cement.
Dwarf Korean Lilacs, many lilacs are available and many would make excellent hedges, however, as hedging goes I would pick this variety. They can be purchased quite small and will quickly grow into a compact mound. A few close together like the ones above would easily make a dense hedge that also blooms profusely in the spring. I would think a very light trim would be all that's needed to form these into a nice hedge. These plants excel in our area and are very undemanding.
Gooseberry, grows easily, has a pretty leaf and bonus berries! This one down my street grows into a large open shrub but I'll bet if you pruned it it would grow into a nice dense shrub. Alpine Current a close relative is also available and can make a nice hedge in our climate.
Burning Bush, Euonymus elatus, Winged Burning Bush, is a very attractive shrub that turns brilliant red in the fall thus the name. They take easily to trimming and pruning and can grow at least 10 feet tall. These shrubs should be planted in full sun for best fall colour. The only drawback in our area is that Jackrabbits love to eat these shrubs when young and will need winter protection.
Siberian Elm, Ulmus pumila, used as hedge material in Eastern Canada takes extremely well to hard pruning and clipping. This tree may not be available for sale as it is considered invasive. Unchecked this will grow into a large tree, over 50 feet, very quickly. The one I have was a volunteer that I have bonsai'd into 3 balls over only 10 or so years, it is now over 10 feet tall. Drawbacks are it must be trimmed several times a year and leafminer leave the leaves exhausted looking in the summer. Pluses are extremely fast growth about 5' a year, this would make a tall hedge quickly, the trimmed plants get very dense and if you make a mistake will quickly grow back. With all the trimming I have never had this plant bear seeds . Being native to semi-arid regions of Asia this tree became popular as a shelter belt tree across the prairies and is still a common sight, there are many wild specimens around the city.
