What to Prune and When to Do it
Knowing what to prune and when to do it can be very daunting. The main aim of pruning is to remove dead or diseased branches and stems on your plant to maintain its health. Pruning can also be undertaken for aesthetic reasons, especially if you have unruly vines or canes that are taking over your garden!
Remove dead, damaged or diseased stems on your plant as soon as you spot them – these stems invite diseases to develop. It’s also a good idea to remove branches that cross over each other as this allows for better air circulation, which again decreases the incidence of fungus or diseases.
Many varieties of hydrangeas, such as mopheads, lacecaps or oakleaf, bloom on old wood. You will often find a raft of different advice on when to prune your hydrangeas. Some gardeners like to prune in Autumn, usually those in warmer areas, to tidy their plants after flowering. Gardeners in cooler areas should wait until Spring when all danger of frost has passed. Leave the spent flower heads on the plant too, if you can bear it, because the flower heads act as insulation and protect the plants and young buds from cold weather.
The important thing to remember with macrophyllas is that they flower on the previous year’s stems, so if you trim them right down to the ground you won’t get any flowers the next season. Trim off straggly growth, leaving behind as many of the fatter buds as possible. On established bushes, cut a few of the older stems down to the ground to reduce overcrowding.
Lacecaps are the same, except in warmer areas it’s best to snip off the flower heads once they’ve faded to stop plants putting their energy into producing seeds. In cooler areas, lacecaps are less inclined to produce seeds.
Spring Flowering Trees and Shrubs
Early Spring bloomers like lilac and rhododendrons produce their flowers on old wood. Prune in late Spring as soon as they finish flowering. Don’t prune too late in the growing season or during Winter as you may remove flower buds, decreasing the amount of flowers for the next Spring.
Summer Flowering Trees and Shrubs
Plants that bloom in summer such as crepe myrtle, produce flowers on new growth from the current season. Prune in Winter while they’re dormant, or in early Spring before they push out their new growth.
The best time to prune a camellia is immediately after it has stopped blooming, which will most likely be in mid winter depending on the variety. Pruning at other times will not harm the plant, but it may remove some of the blossom buds for next year.
Branches can be cut back at almost anytime of the year. Try avoid late Autumn pruning as new growth that starts after late season pruning won’t get a chance to harden off before Winter starts. If you want to do major pruning, it’s best to do this in Winter when the shrub is dormant.
To maintain a solid wall of green, shear the new growth frequently during the early part of the growing season (late Winter to early Spring or mid- to late Summer are some of the best times to prune hedges). Keep the top narrower than the base so that the upper branches don’t shade the lower ones. Stop shearing the hedge about six weeks before your areas average first frost.
In most parts of NZ, rose pruning is carried out in July through to mid-August. Prune established plants to remove dead and diseased wood and any branches that may be crossing over each other. Opening up the centre of your plant and improves air circulation which lets in more light and prevents disease. Angle cuts at a 45 degree angle outward (away from the centre of the plant), cut back canes to the healthy green wood.
Snipping off spent flowers throughout the growing season prompts more blooms. Let the last roses of Summer wither on the canes. This allows plants to prepare for Winter by developing hips.
Roses such as floribundas, hybrid tea and miniatures, bloom on new wood and benefit from removing half to two thirds of the plant’s height, and all but 3 to five canes.
Climbers bloom on old wood, so wait until after the flowers fade before you cut back canes older than a few years. Prune for a balance of old and new canes.
Shrub and old garden roses need only a light prune to remove old or weak stems or to maintain shape.
Deciduous Shade Trees
Trees like oak should be pruned in Winter when they are dormant. It’s easiest to see the branch structure at this time of year too, and you’re less likely to spread diseases through pruning wounds. Avoid pruning in late Summer.
Trees such as maple and birch produce a heavy sap flower when pruned in Winter, although this may be unsightly it does not harm the tree. To avoid the bleeding, you can wait until the leaves have expanded in Summer and prune then.
Deciduous Fruit Trees
Apples, peaches, pears and plums should be pruned in mid-Winter. Although winter pruning removes some of their flower buds, the goal in pruning fruit trees is to open up the tree to allow in more light for a better crop of fruit, rather than to get maximum bloom.
Citrus don’t necessarily need to be pruned unless you’re trying to maintain shape or remove any diseased or damaged wood. Harvest fruit prior to pruning. The best time to prune your citrus is after fruiting in Spring. In frost free regions, pruning can be done at any time of year. In frost prone regions, avoid pruning in Winter because this will push soft new growth that hasn’t had time to harden off, and it will be damaged by frost.
We would suggest if you are growing your feijoa as a tree then prune it so ‘a bird can fly through it’. This will give air circulation to the fruit and create a nice feature looking tree. If you are keeping your tree as a hedge then prune the shrub back by 1/3 once a year after fruiting has finished.
There are no set rules when it comes to pruning avocado trees. You should aim to maximise the amount of light the tree gets and also manage tree size and shape. Dead wood removal at any time is encouraged. Major structural pruning in Summer should be avoided to prevent sunburn.
Perennial flowers look best if you remove faded blooms – this is called deadheading. Most perennials will push out another cycle of blooms after deadheading.
Deadhead annual flowers regularly to keep them blooming well. Removing old flowers prevents them from setting seed and allows them to put more energy into blooming.
The parts of blueberry bushes that produce the most are often a few years old. To maintain a continual supply of productive wood, prune out about a third of the oldest stems on these shrubs each Winter.
Raspberries and blackberries grow on long stems called canes. On most types, the cane doesn’t fruit until its second year of growth. After bearing fruit, the cane dies. Remove two-year-old canes soon after they finish bearing. They won’t fruit again, and they can spread disease if left to grow
Grapes are vigorous growers and need to be extensively pruned to keep them productive. Grapes fruit on lateral shoots from the current season’s woody growth. Prune all grapes close to the lateral arms each year during the dormant season to produce the best fruit.