Pruning citrus gets almost as many hits on social media as pruning roses. Unlike roses, citrus doesn't need annual pruning to produce good quality fruit in quantity.
So, why prune a citrus tree?
To shape a new tree
To make harvesting ladder-free
To rejuvenate an old unthrifty tree
To reduce pest and disease problems for existing trees
The most important time to trim your tree is straight after planting, the next most significant is one year later. This is all about setting the shape of the young tree and keeping the canopy within picking distance. Essentially this results from my ladder phobia. Ladders feature in more serious garden injuries and even deaths than any other tool so keeping your citrus tree compact and within easy picking reach from the ground is the healthy alternative.
The best tool for this early shaping is a pair of hedge trimmers. Expect to make one cut with your shears in year one and about three cuts in year two. This treatment will set the tree up for heavy cropping in subsequent years, as the effect is to promote fresh shoot growth. Young shoots are where flowers and subsequently fruit, come from.
Taking the top off the canopy of a tall existing tree is an effective way of getting access to your fruit.
Suitable tools can include a chainsaw, hand pruning saw, long-handled loppers and Powergear tree pruners.
The best time is immediately after cropping before the onset of hot weather. One hint when exposing branches to direct sunlight you can unwittingly open up the bark to sunburn, as the trees are quite susceptible. Paint the newly exposed stems with a white acrylic outdoor paint. This reflects heat and prevents burning which also has the effect of encouraging disease and insect attack.
Old lemon trees are the usual suspects here and the treatment is brutal. Fortunately, the tree can be completely reinvigorated and brought back into strong cropping. Tools needed include chainsaw or bow saw as well as branch loppers. Cut back main trunks and branches to around chest height. It's likely that you will be left with 4 or 5 bare trunks so yes it's brutal. Painting the exposed trunks is even more critical here to prevent sunburn. New suckering growth will explode around the cut. It's a good practice to allow only 2 to 4 shoots per branch to remain and go on to grow into the new canopy trunks of the tree. This level of pruning only needs to be repeated every 8 to 10 years.
Perth has copped a few new pests from the east including citrus leaf minor and more recently citrus gall wasp. Both problems can be treated by pruning. Citrus leaf minor attacks the youngest foliage and once the grub hatches it eats out the cells between the top and bottom surfaces leaving a squiggly silvery mark within the leaf.
Mature trees can tolerate damage from this pest without much trouble, however younger one to 3 three-year-olds can be badly damaged. Using hedge trimmers you can remove the recently affected foliage. The insect needs to be destroyed and one of the best methods is to pack the pruned foliage into a black plastic bag and leave this in the sun for a few months to solarize the contents. Then the cooked leaves can be disposed of.
The Gall wasp lays eggs in young stems, which swell up in response. These swellings, which are tapered at both ends, need to be pruned out completely. Once again it's best to either solarize or dispose of these swollen stems through your rubbish system so as to prevent the young wasps emerging and infesting your or neighbours citrus trees.
Fruit fly can be a serious problem, particularly for mandarin and tangelo. My preferred control consists of covering the tree with shade cloth when fruits are about half their mature size. In order to easily accomplish this exclusion netting approach, I have found it necessary to reduce the height and spread of my trees, in order to easily pull the cover over the canopy. A quick hint I tie off the shade cloth around the trunk of the tree so the pesky fruit flies can get under the cover to do their egg-laying work.