HOW TO PRUNE A
There are three forms of plum tree, the most common is the bush form, the less common are pyramid and standard forms. Occasionally people grow plum trees in a fan form against a wall.
This article deals with pruning a bush shaped plum tree, by far the most common.
Plum trees differ from most other fruit trees because they should only be pruned when they are in full growth. In the UK, the best time to prune your plum tree is in early July 2014, never in winter when they are dormant. The reason is that pruning your plum tree when it is dormant will expose it to the risk of Silver Leaf.
HOW TO PRUNE YOUR PLUM TREE
Many books and website articles over-complicate the task of pruning plum trees but in truth they are far more tolerant of incorrect pruning compared to apple and pear trees. The basic principles to adhere to are to prune once a year at the time given above and to prune them to a wine goblet shape with the centre of the tree relatively free from branches and foliage.
The "wine goblet" principle of pruning encourages the branches to grow up and away from the centre of the tree. The majority of shoots growing into the centre of the tree are pruned away completely and those growing outwards are hard pruned to encourage more growth this and next year.
The diagram shows only two of the main branches coming from the main stem although if you are lucky you might manage all three or four coming from the main stem. In many cases though, only two main branches will come at the correct height. Another main branch should then be left to grow from the original two branches (see branches 3 and 4 in diagram)
It will be impossible to get it exactly accurate, but however many main branches you choose to have, they should be roughly evenly spaced out to give the tree balance.
For year one pruning (see picture below) we suggest pruning the tree to a 1m / 3ft height but this is only a rough guide. You want at least two branches to form from the main stem and these will come from buds clearly visible. So in year one you may want to prune the main stem slightly higher so that a promising bud or two, in the correct position, is left on the main stem.
If you prune your plum tree at the correct time of year (see section above) you will be pruning your plum tree when the fruit has already started to form. This will lead you into the temptation of under-pruning it to avoid cutting off fruit bearing shoots and stems. Avoid the temptation and prune the tree correctly! Most plum trees form far too much fruit and this can be severe enough to cause the branches to break under the weight, Victoria plum trees are a prime example of this. Correct pruning will indeed remove some potentially fruit bearing stems but this will only improve the health of the tree and result in larger plums.
Pruning in the first and second year of a plum tree's life is easier but slightly different because there are fewer branches to prune. The three diagrams below explain how to prune a plum tree in years one, two and three.
FIRST YEAR PRUNING
Read the above section entitled "How to Prune Your Plum Tree" above carefully before starting year one pruning. It will help explain the overall process and aims of pruning your plum tree.
First year pruning is very easy, simply prune back the stem to about 1m / 3ft high in July. If you are intending to grow your plum tree as a half-standard bush then prune to 1.2m / 4ft or 1.6m / 5ft for a full standard.
SECOND YEAR PRUNING
Prune back the main branches to a length of about 30cm / 12in. Prune back any side shoots to a length of 15cm / 6in. Prune weak shoots away completely and trim back any stems which are crossing. During the pruning cut the shoots and branches to an outward facing bud to try and achieve the goblet shape with a clutter free central part.
THIRD YEAR PRUNING
Third year pruning is the same as second year pruning but particular attention should be paid to keeping most of the centre of the plum tree free from branches. This helps the overall health of the tree by allowing free air circulation thus avoiding fungal diseases.
PRUNING IN LATER YEARS
Prune the top stems and branches by about a third to keep the plum tree from growing too high. Other stems and branches should be trimmed to maintain an overall goblet shape. Once again, prune shoots growing into the centre of the tree to keep it relatively open.
FINAL THOUGHTS ON PRUNING PLUM TREES
The tree on the left (above for mobiles) is not ideally formed, it has a bias to one side which makes it slightly unbalanced. But nature has bulked out the correct branches to make sure the tree remains relatively stable. And the proof of the pudding is in the eating, this plum tree produces lots of delicious fruit year after year!
Plum trees require very little care throughout their life (aside from a yearly pruning) but will produce of their best if you thin the fruit, mulch the surrounding ground and give them an annual feed. These are all described below.
THINNING PLUM FRUITS
Plum trees are well known for producing vast amounts of plums in some years. This is not good for you for two reasons. First, if too many plums are produced, each individual fruit will be small and may well not ripen fully. The second problem with over-production of fruit is that the sheer weight of the fruit can cause branches to break and they don't break cleanly in most cases. This will ruin the structure of the tree and often leave jagged open wounds which are a source of fungal diseases.
Judging how much fruit should be left on your plum tree is really a matter of experience gained over a couple of years, every tree is different. But as a general rule thin young fruits so that at maturity 3cm / 1in will be left between each fruit. The best time to thin plum tree fruit in your area is late June 2014
MULCHING PLUM TREES
Plum trees require a constant source of moisture at their roots especially when the fruits are forming. A mulch with any organic matter around the base of tree each spring will go a long to providing these conditions. If you have no organic material to hand then think again, a mulch of grass cuttings will do the job very well. If you have the money a bag of chipped bark will provide a long-lasting mulch which will retain moisture and also keep weeds away.
A long lasting organic feed such as blood, fish and bone (three handfuls per tree) will provide them with an excellent tonic. It is best applied in spring just before you spread mulch around the trees.