A "hedge" is a wall composed of plants. Some are purely decorative, while others serve primarily a practical function. Hedge plants used decoratively are often trimmed to precise sizes and shapes and include evergreen and deciduous shrubs. Such shrubs may also serve the practical function of affording a property some security. Here are some resources to get you started if you are interested in creating a "living wall":
Almost any row of densely growing hedge plants will enhance security to some degree. If you need a higher level of security, but still wish to stick to hedge plants rather than fences, select shrubs or small trees that have thorns (e.g., hawthorns), or at least prickly leaves (e.g., holly; see below).
But security is not the only practical function that hedges can serve. Hedges may also be used to create privacy screens or windbreaks, in which cases small trees are often employed (either exclusively or mixed with shrubs). The plants in such privacy screens or windbreaks are commonly allowed to grow naturally, rather than trimmed to a particular size and shape, unless the grower wishes to combine decorative and practical functions.
Below I discuss examples of hedge plants, with links to more detailed information about each. I'll begin with hedge shrubs. Note that not all hedge shrubs should be meticulously trimmed so as to form sculpted, even surfaces with straight lines.
Only three of the shrubs discussed below are typically trimmed in this fashion (forming the "classic" hedge, if you will):
Examples of Evergreen Hedge Shrubs
Japanese holly (Ilex crenata) looks more like a boxwood shrub than holly shrub, bearing small, oval leaves. Many cultivars of this broadleaf evergreen are available; for hedge plants, most people select those that reach 3'-4' in height, with a similar spread.
Japanese holly is hardy to zone 6. But English holly (Ilex aquifolium), with its prickly leaves, makes a better hedge plant if you wish to combine security with aesthetic considerations. Some hollies grow tall enough to serve as privacy screens. You can learn more about the hollies in this article:
Boxwoods are the classic hedge plants. These broadleaf evergreens were adored by aristocratic Europeans for centuries as defining elements in formal garden design. To learn more about boxwood, please consult the following article:
Other broadleaf evergreens suitable as hedge plants include the mountain laurels. A bonus with mountain laurels is that they bloom in late spring-early summer. Don't try to trim laurels as you would boxwoods. For more on these hedge plants, please see the following article:
Among needle-bearing evergreens, yew bushes are perhaps the classic hedge plants. They are popular, partly because they tolerate shade. Some yews grow tall enough to serve as privacy screens. However, yews are slow growers. You can learn more about the yews in this article:
Examples of Deciduous Hedge Shrubs
Deciduous hedge shrubs look great while they're in bloom, but just so-so during the winter.
Also, because they drop their leaves and stand naked for part of the year, deciduous shrubs make for less than ideal privacy screens. Three of the deciduous shrubs most commonly found in hedges are rose of sharon, forsythia bushes, and lilac bushes. But you probably won't want to prune any of these as meticulously as you would, say, boxwood. Most people agree that forsythia, in particular, looks best when it is allowed to "have a bad hair day." To form a hedge with such a shrub, simply plant several of them in a line. Don't fuss with making them conform to precise, predetermined dimensions.
Examples of Other Hedge Shrubs
Like mountain laurels, azaleas and privets are broadleaf shrubs that put out flowers (the former much more impressively). However, not all varieties of azaleas and privets are evergreen; and those that are will not necessarily grow well in your zone.
Check with your local county extension to see if you can grow evergreen azaleas or privets in your area. If not, you can treat azaleas and privets as you would the other hedge shrubs in the prior category (deciduous).
If you my recommendations for hedge shrubs and you feel that such a "living wall" could enhance your landscaping, but you know nothing about pruning hedges? No problem. Below, I tell you about the basics involved in the operation. And in case you wish to take your education on the subject to the next level, I also provide a link that will bring you to a full tutorial (with pictures), showing you how to shear your masterpiece with precision.
How to Prune Hedges
Do not prune hedge plants so as to form a wall straight-up-and-down. Rather, prune hedges so that the base is wider than the top (a shape sometimes referred to as an "inverted keystone"). This will allow sufficient sunlight to reach the growth at the bottom, keeping it healthy. To aid you in the task of pruning hedge plants, you'll probably want to invest in a hedge trimmer. And as I relate below, you'll also need a tape measure.
How do you prune hedges so that they come out straight? And how do you get the tops level? The key is to lay out a foolproof network of guides before cutting, using stakes and string. Pruning hedges is truly a case of, "You get what you put into it." If you measure carefully with a tape measure and place your guides exactly where they should be, then you'll get a precisely trimmed hedge. But if you just try to "eyeball it," then the end-result will reflect your haste. It's that simple. Hedges are not for homeowners who desire low-maintenance landscaping.
Thus to prune hedges with precision, there's a lot of preparation involved. Essentially, the preparatory work entails framing the area (the "inverted keystone" shape mentioned above) that you want the finished product to occupy. This preparation will probably take you longer than the trimming itself. That's the bad news. But the good news is that, with the guide strings in place, you can proceed to prune hedges with total confidence that your cuts will be unerring.
I show you how to set up those guide-strings, step by step, in my tutorial on trimming hedges, replete with pictures.
A word is in order concerning trees that are used in hedges or as windbreak trees. No, not all hedge plants are shrubs, such as those discussed earlier.
Arborvitae trees have a dense growth habit that makes them popular privacy screens or windbreak trees (arborvitaes are also found in shrub-form if you're seeking a shorter hedge). There are many types of arborvitae; they come in various sizes, shapes, and colors.
In Europe, European Beech Trees have been used for centuries as privacy screens and windbreak trees. Windbreak trees are commonly allowed to grow naturally, rather than trimmed to a particular size and shape, unless you wish to combine decorative and practical functions.
Canadian hemlocks (Tsuga canadensis) are among the easiest trees to prune into hedges. MacPhailWoods.org states, "Prune hemlock lightly but often during the first few growing seasons (two to three times from late June to late August for two to three years). After three years prune once, in late June, as with white spruce." The site cautions against cutting the leaders until the hemlock hedge or windbreak has attained the height you envisioned for it.
There is even a tree known as the "hedge maple." I introduce you to it at the end of my article on the different types of maples.