Unlike deciduous trees, evergreen plants don’t shed their leaves at the same time—when the cold season arrives—but replace them gradually over several years, depending on the plant. Generally they are trees and shrubs, but they can also be climbing plants. You can make use of evergreens to plant a hedge.
In the garden evergreens make up a permanent plant structure that stays green all year round, even when other plants lose their leaves before becoming dormant. Nature has given them leathery leaves, cold-tolerant tissues and the ability to maintain minimal photosynthesis through the winter. There are also evergreen invasive plants—such as hypericum or periwinkle—but today we will focus on evergreen garden trees (particularly conifers), shrubs and climbers.
Which evergreens should you choose for your garden?
According to the shape of the leaves, evergreen garden trees can be divided into needle-leaf and broad-leaf trees. Many conifers have needles or scales instead of leaves, hence they are also called needle-leaf trees, and all are evergreens with the exception of the larch. Here are some examples of conifers for your garden: firs, cypresses, false cypress, pines, yew and thuja. By contrast, broad-leaved evergreens, like the olive tree and the laurel, have wide and flat leaves and are a common feature of Mediterranean scrub.
Evergreens are not just trees—plants with a trunk from which branches develop at some distance from the ground—but also shrubs, which have no distinct trunk and develop branches nearer to the ground. The difference isn't always apparent: some shrubs can be grown as trees and vice versa.
Various varieties of evergreen garden shrubs can be used as hedges: barberry, boxwood, camellia, silverberry, photinia, juniper, cherry laurel, lavender, privet, Mahonia, pyracantha, cheesewood, rhododendron, yew and viburnum.
Another sizeable group of evergreens are climbers, which are plants that develop quickly by climbing walls, supports or other vegetation using various modes of attachment (tendrils, hooks, etc.). Common evergreen climbers include chocolate vine, Bignonia, Bougainvillea, some varieties of honeysuckle, clematis, jasmine, false jasmine, creeping fig, ivy, passionflower and leadwort.
How to prune evergreens
Generally speaking, pruning evergreens is not demanding. For conifers, you should limit pruning to the removal of dead, broken, diseased, weak and badly oriented branches. The best time of year to prune firs and other conifers is at the end of winter. Get the lowdown on pruning pines and firs in our article on pruning the Christmas pine tree.
To maintain their structure and smooth surface, conifers typically used as formal hedges (i.e. with a regular, box shape), such as the yew and thuja, need to be trimmed back a couple of centimetres every 10-15 cm of growth. The cutting frequency depends on the rate at which the plants grow.
As for evergreen shrubs, in addition to removing dead, diseased or broken branches (here in Italy we call this “rimonda”, or “cleaning”) in late winter, thicken the foliage in late spring and late summer (May/September) by cutting off the tips of the branches. In principle, this applies to evergreen shrubs used both for formal hedges and for more elaborate figures and shapes (we are talking about topiary).
Even free-form evergreen shrubs (i.e. those with a non-geometric shape) don’t require extensive pruning: in addition to “cleaning” at the end of winter, in late spring and late summer do some containment pruning to keep the plants at their current size. You can prune them between late winter and early spring to strengthen their branches, but not in the case of fast-growing, vigorous plants like the cherry laurel.
As a general rule, evergreen climbers also require light pruning to eliminate dead, broken, diseased, old, weak, excess or misplaced branches. The ideal period for pruning these evergreens is late winter/early spring (this is a general rule of thumb, with exceptions: for example, false jasmine should be pruned in spring/late summer).
Speaking of jasmine: there are several varieties including evergreen and semi-evergreen (which only lose part of their foliage). They are all sensitive to cold temperatures, so they should be grown in a sheltered spot: here are our suggestions for protecting plants from the cold.
Depending on the size of the branches you need to cut, the type of evergreen and the workload, you can use manual pruning tools—such as pruning shears, a pruning saw and a lopper—or alternatively a hedgetrimmer, chainsaw or telescopic pruner. Even more importantly than for other jobs, when pruning you should wear appropriate protective clothing: check out our article on personal protective equipment for different gardening tools.
Hedgetrimmers and chainsaws are essential cutting tools in the garden maintenance toolkit for anyone with a passion for gardening (not just professional gardeners): we talk about them in our articles on DIY gardening, choosing the most suitable pruning chainsaw and electric, battery or petrol-engine hedgetrimmers.
Other tips on caring for evergreen plants
Evergreen garden hedges, shrubs and trees should be fertilised periodically in their young and adult stages. Fertilise hedges, as well as other evergreens, in autumn/winter (between October and December, avoiding frosty spells) to restore soil fertility, by replenishing nutrients that have been extracted by the plants to grow and bloom during the year. Fertilisation is especially important for hedges because they are concentrated into a confined space, where the soil is more likely to become more depleted.
Use organic fertiliser such as manure, or mature or pelletised compost (on the subject of compost, here's how to make your own). In spring, you can fertilise evergreens using nitrogen, phosphorus, and potassium (NPK) based mineral fertilisers, to help them develop foliage.
Organic fertilisation is a great remedy for soil exhaustion (loss of fertility): in this article you can find out how to prevent it and how to improve soil conditions.
While it is common for conifers to dry out inside the canopy because new vegetation grows on the outside, this could also be the result of an ongoing disease. Why do pines or firs dry out and what countermeasures are there?
Desiccation of leaf tips and drying and dropping of foliage inside the canopy can be caused by lack of water, other environmental stresses or fungal disease. In the latter case, the plant canopy should be treated with copper salts.
What about when hedges dry out? Again the reason may be fungal disease: the remedy for a diseased hedge (more often a conifer than a broad-leaf variety) is Bordeaux mixture, which you can apply both as a preventive and curative treatment.
Evergreen hedges can be attacked by insects such as aphids and scale insects. Cosmetic damage can also be due to white patinas such as powdery mildew—which is common in the cherry laurel, caused by fungi and treatable using sulphur-based products—or honeydew produced by flatid planthoppers. In addition, honeydew, together with aphids, scale insects and so on—which can be treated using mineral oil or natural products—attract fungal species that cause sooty mould (a black patina that inhibits photosynthesis in affected plants).