Pruning: Why, When, How and Where?
Pruning: Why, When, How and Where?
When a plant grows too large for its space or is blocking the view from a window, it’s time to remove or restrict unwanted growth.
- Pruning dead, injured, or diseased wood is an ongoing activity. Trimming also needs to be done regularly when you need to maintain a specific form such as a hedge or topiary evergreen.
- For shaping hedges, leave the bottom wider than the top so the top growth doesn’t shade the lower.
- For older shrubs like Forsythia and Lilac which can become very dense and tend to bloom less with each year, they need serious rejuvenation. Cut out about 1/3 of the stems right down to ground level to allow light into the centre of the plant, thereby encouraging new branches to grow that will flower.
- Dogwoods are loved for their yellow or red twigs in winter but when the old wood loses colour it will need to be removed completely. This process stimulates new growth and these thinner twigs will have the brightest colour.
- Fruit Trees are pruned to allow as much light as possible onto each branch. More light increases flower and fruit production.
When to Prune
- Fruit Trees and some Shade Trees – these trees can be pruned in February/March before growth begins and you can clearly see the bare framework. At this time, cut close comparatively quickly.
- Birch, Honey-locust, Magnolia, Mulberry, Maple, and Linden – these trees bleed profusely in spring and should only be pruned in July.
- Spruce and Fir – these evergreens do not usually require trimming but if you need to promote density you can cut the new growth back by half in June before it hardens off.
- Mugo and Austrian Pines – to keep the growth of these evergreens thick and compact, prune a 1/2 to 3/4 of their soft, creamy-white candles in mid to late June.
- Junipers, Cedars, Euonymus, and Boxwood – these Evergreens and Broadleaf Evergreens put on all their growth in May and June. You may find it easier to shape them once in summer rather than trim them in spring and then again in July/August.
- Clematis – has two flowering times depending on variety. May/June flowering Clematis like Nelly Moser, The President, and Bee’s Jubilee blossom on the previous year’s wood. Therefore, like shrubs, they can be pruned lightly after flowering. They will produce a second, smaller flush of blooms in September on the young wood. Summer-flowering varieties like Comtesse de Bouchard, Ernest Markham, Jackmanii, and Ville de Lyon flower on new wood grown since spring and can be pruned back to 50 cm (20″) in April. This is done to promote blooming and foliage as far down the vine as possible.
Flowering deciduous shrubs fall into two pruning categories.
- All shrubs that bloom before the end of June form their flowers the previous season on last year’s growth. They include Magnolia, Forsythia, Lilac, Flowering Quince, Bridalwreath Spirea, Deutzia, Mock-orange, Flowering Almond, and Purpleleaf Sand Cherry. If you trim them in spring you’re cutting off this year’s flowers. So, prune them immediately after they finish flowering.
- Summer-flowering shrubs like Tamarisk, Butterflybush, Rose of Sharon, Weigela, Hydrangea, Kerria, Caryopteris, Potentilla, and pink-flowering Spirea can all be pruned in April because they set their flowers on this year’s growth. Fall pruning is not recommended for them because the new growth, stimulated by the trimming process, may not have enough time to harden off by winter. This soft tissue often dies back with cold temperature and needs to be pruned in spring.
How to Prune
Handheld pruning shears, called secateurs, come in two forms.
Scissor Secateurs – known as a bypass pruner and makes close, precise cuts.
Anvil Secateurs – must be kept sharp at all times so the bark isn’t crushed against the bottom platform.
- Any handheld pruner will cut stems up to 2 cm (0.75″) in diameter.
- For larger branches up to 4 cm (1.6″) thick and roses use long handled lopping shears. Again, they come in a Bypass or Anvil action with long handles for better leverage.
- To cut even thicker branches a Pruning Saw is perfect. The folding type is very practical as you can safely close the sharp toothed blade for storage.
- To make cuts higher up use a Pole Pruner which has a handle that is extendable. In this case you pull a rope attached to a head that cuts branches up to 2.5 cm (1″) in diameter. This cutting head can be placed with a curved pruning saw for thicker branches.
- Lastly, Electric Trimmers make quick work of shaping hedges and pyramidal evergreens
- Manual Hedge Shears are better for small jobs when you need precise control.
*Keep all your tools sharp and disinfect them often to prevent the spread of disease.
Where to Prune
- For shrubs, roses, and vines cut about 1 cm (0.4″) above a bud or leaf at a 45° angle.
- Roses are pruned above outfacing buds so the centre of the plant maintains good air circulation thereby lessening the chance for disease.
- Plants that are bare in the middle can be pruned above an inward facing bud to direct the growth there.
- Tree limbs are completely removed back to the main trunk when they cross each other, cause friction or are just too close together. Branches that form a narrow angled crotch with the trunk should also be removed while branches forming wide angles with the trunk should be retained.
- When establishing a young tree, be aware of the height of the first set of branches from the ground so someone walking under isn’t injured.
- Pruning paint or paste is applied to fresh cuts on branches that are 2.5 cm – 5 cm (1″ – 2″) thick or more. It prevents penetration by insects or disease while the tree heals itself naturally over a longer period of time.
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