If you never pruned your Plum tree it would still crop well but it would just grow large and sprawling. So the ideal is to prune it to a good shape in the early years and then just maintain that shape as time goes on. The shape you want to achieve is an Open Centre, also known as the Vase Shape, as this method lets plenty of light and air into the centre of the tree.
The first rule for pruning plums is this: Never prune plums in the winter! This is because of the risk of a disease known as Silver Leaf which attacks the tree and can cause huge damage. When the tree is pruned in the summer months, the growth is strong and the sap is flowing and this prevents the disease from entering the pruning wound. It is best to always paint the cuts with a wound paint to protect the tree - and remember to sharpen your secateurs. It is advisable to also disinfect the secateurs as you move from tree to tree.
What sometimes mystifies people is the different types of buds on fruit trees; what is a fruit bud? What's a spur? The definition of a Spur is:
a small lateral branch on a fruit tree which bears flower buds.
The little pointy spurs are fruit buds. Each one of these will bear one or more fruits so you'll have far too many. Either thin the fruit, or you can thin the little spurs themselves before they set fruit.
Plums bear much of their fruit on lateral spurs that are two years old or older. These spurs are usually 20 - 30cm long. It is necessary to prune for renewal of some spurs each season, although most of the new growth is removed. Depending on the variety, 20 - 40% of the fruitwood around the tree is renewed annually by leaving young shoots and removing old wood. This ensures a balanced crop that does not need thinning.
The first year:
Just as the buds are starting to break in the springtime, cut back the central stem of the tree to a bud at about two thirds of the height of the maiden tree. Shorten all the lateral branches to about 15cm to allow the main stem to thicken.
In mid summer, chhose about four or five evenly spaced primary branches around the main stem - these are the ones you will use to create the Vase shape. Pinch out the growing tips of all the other branches at about four or five leaves, including those lower down on the stem.
The second year:
In spring, choose four or five branches that have formed wide angles with the stem. Cut back each leader of those se1ected by a half to an outward facing bud. Remove the remainder, including the lower laterals left the previous year to thicken the stem. In the summer remove any suckers that appear from the ground and remove shoots on the main stem below the head.
Wairere Nursery 826 Gordonton Road, R D 1, Hamilton Ph: (07) 824 3430 Email: Open 7 days 8:30am-5pm