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Great Gardening: A pruning primer

Pruning is, in my opinion, the landscape job that more people do badly than any other task. (Watering is a close second.) Many homeowners do it poorly – typically flat-topping shrubs that don’t deserve it – and often at the wrong time of year.

Some untrained landscapers might prune poorly as well. The educated landscaper (CNLP) has been trained in correct pruning methods and timing – but even then a homeowner or condo association sometimes insists on a certain look or pruning regimen that isn’t ideal for plant health or preferred technique.

What’s surprising: In spite of all the unfortunate bad clipping out there – often called “whacking back the bushes” – basic pruning is not that difficult. (At another level, some kinds of pruning are an art form.) For everyday purposes, once you acquire the basic theory and timing, pruning is an enjoyable skill. If your landscape has the right plants for the sites, most of you can handle pruning. It may be much less work than you think.

This is a simple primer that I hope encourages you to start looking at the shrubs and trees around you and evaluate which need pruning. Then attend a class or get a book. Practice first with the “think method,” and then prune some shrubs in a field or in back of the yard. Use hand pruners or loppers – this is not chain saw or electric hedge trimmer work.

What needs pruning?

Three situations warrant definite cuts:

1. Cracked or broken branches: Cut them off just above a healthy branch.

2. Diseased or dead branches: In case of disease, get a diagnosis. In general make the cuts several inches beyond the diseased section.

3. Rubbing and crossing: This is where judgment and art enter. Branches that are rubbing together will lead to a wound which leads to damage, poor structure or disease. You must choose the desirable branch and cut out the other.

When a plant is too big: This is the most common reason that most people prune. When the shrub crowds the window or sidewalk, or rubs on the house, that plant was put in the wrong place originally. Now something must be done – thoughtful pruning or replacement with a plant that will not outgrow the location.

If you are routinely “trimming” plants to keep them to a certain size, they weren’t the best choices for the spot. A mature plant, growing naturally in the right place, is a beautiful thing.

Most plants can grow attractively to their mature sizes without yearly pruning. Corrective, selective pruning – of broken or misdirected branches – is all that is required.

Other understandable reasons for pruning:

• Some plants become so crowded with branches in the center that sunlight can’t get in to support foliage, flowers or fruit. If poor pruning (buzz cut) was done in the past, all the growth is on top.

• Some plants are prone to diseases that thrive in crowded conditions; thinning them to increase air flow helps.

• Some plants are intended to be hedges, topiaries, espaliers or Christmas trees, all different topics entirely.

• Some orchard trees are pruned low and flat to facilitate maintenance or harvesting. Some fruit plants or roses are pruned to increase fruit or flower size.

• Some trees are “limbed up” to expose attractive trunks or to remove branches that impede other plants or pedestrian traffic.

Timing of pruning

Late winter is the best time to prune most shrubs and trees, when they are dormant. The plant’s stored energy (food reserve) is in its roots. Once the plant breaks dormancy and leaves form, the food reserves are in the leaves; you lose and waste those carbohydrates when you cut off branches.

Also, in late winter few insects or disease spores are present to invade the wounds, and the wounds seal over quickest with spring coming. (Fall or earlier winter pruning are less desirable because wounds heal more slowly, leaving the plant vulnerable to disease or pest invasions.) Without leaves present, you can also see branching structure and judge where to cut.

Exceptions to late season pruning

• Spring flowering plants: Early pruning cuts off those flowers. Examples: azalea, crab apple, flowering dogwood, forsythia, lilac, rhododendron, wisteria, climbing roses. Late winter pruning does not hurt these plants – all the previously mentioned benefits are valid – but you’ll miss some flowers.

• Conifers: Needled plants such as spruces, firs and pines have different pruning needs and timing.

• Bleeders: Some trees apparently “bleed” when pruned in early spring – the reason we harvest maple sap for syrup then. While this oozing is dramatic (and may drip on cars or sidewalks), most scientists say it does not harm the tree. Wound painting, unless recommended by a certified arborist working to prevent specific diseases, is not recommended. If you want to avoid the bleeding, prune maples, walnuts, birches or elms earlier in winter or in early summer. (For large trees, always consult with an arborist.)

How to choose where to cut

Remember this principle: Your cut signals the plant where to push out new growth. If you flat-top or found off a shrub, it tries to push out new shoots all over – fine, if you want a ball-shaped spiraea. If you want a graceful viburnum, then make varied, selective cuts of crowded branches inside the shrub.

Always cut just above another branch or bud, preferably one that faces outward. After you cut, the energy will go into the bud or branch you left behind. The idea is to let sunlight reach as many tree or shrub branches as possible.

If you are cutting limbs of large shrubs or trees, learn to recognize a “branch bark collar” or ridge – the thick part where the limb attaches to the trees. A proper cut is outside that thick collar, angled slightly inward. Never leave stubs.
You can see there is more to learn, beyond these basic concepts. In classes and articles coming soon, I will address specific pruning examples – vines, conifers, and the all-time most asked question about pruning hydrangeas.

Sally Cunningham is a garden writer, lecturer and consultant.

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