When and how to prune plum trees

Plums are one of our favourite fruits and there is no doubt that those picked fresh from a homegrown tree are so much tastier than those from the supermarket.

However, in order to enjoy a regular supply of plums each year, it is sometimes necessary to give them a prune. (Not the dried plum variety of prune of course!)

I started my career about 25 years ago in the fruit department at RHS Wisley and was lucky to work under an amazingly knowledgeable person called Jim Arbury, who is the property’s fruit-growing specialist.

I caught up with him to find out when to prune plum trees and how to give them a bit of tender loving care, to help increase your yield and keep the plant healthy.

So, sharpen your secateurs, and get ready to discover when and how to prune plum trees.

1. The best time of year to prune plum trees

Only prune when the tree is in growth

Larger branches that are growing into the centre of the bush can be pruned back to a lower branch using a pruning saw in spring (April or May). Smaller pruning cuts should be made between mid to late summer.

Prune the new growth of leaders (the shoots at the end of the branches) back to eight leaves, and other lateral branches along the stem back to six leaves.

Arbury explains: “Plum trees should never be pruned during the winter because they are susceptible to bacterial canker and silver leaf problems, which are both diseases which can end up killing your tree.

“Pruning wounds during winter will make them more prone to these infections. This is because the trees are not in active growth and so do not have time to heal, leaving open wounds for weeks afterwards.”

Arbury continues: “As a general rule of thumb, larger branches should be removed in spring, as it gives them the entire summer to heal, whereas smaller pruning cuts can be made between July and early September.”

2. Don't prune plum trees in the rain

Why it's important to only prune in dry weather

Not only is the time of year important when it comes to pruning, but the weather also needs to be dry; not always easy in an English summer.

“It’s really important not to prune plum trees in the rain,” explains Arbury.

“In fact, the same rules apply for all stone fruits (cherries, damsons, peaches etc). This is because the rain splash and damp conditions will spread disease throughout the pruning wounds.

"So ideally, you need to check the weather conditions before setting out with a pair of secateurs.”

Arbury continues: “In fact, not only should it not be raining on the days you are pruning, but it needs to be dry for at least two days afterwards to ensure wounds do not get wet.”

3. Get the right shape

An open centre bush is best

Arbury explains it is important to know the desired shape of the tree before you start wielding secateurs or a pruning saw. The most common shape for a plum tree is a “bush”. 

Arbury says: “A free-standing plum tree (often called a ‘bush’) should have an open centre. This allows for better air circulation, which helps avoid diseases.”

A bush should have four or five main branches coming off the centre of the trunk, creating a “goblet” shape. 

The trunk should be left clear up until one metre (3ft 3in) high, although this height will vary depending on the eventual size of the tree.

4. Cut back above a shoot

Otherwise the whole branch can die

If you need to reduce or alter the shape of the tree by removing large branches that have outgrown their space, you should always look to cut just above another shoot lower down.

Just cutting back anywhere along a branch can lead to the branch dying back.

By cutting to a lower branch, you ensure the vigour of the tree will be taken up from that location, hopefully resulting in healthy new growth.

When pruning the younger shoots, cut them back to just above an outward-facing bud. This is to ensure the branches don’t grow inwards and shade the centre of the tree.

5. Don’t over-prune your plums

As a general rule, plums do not like to be pruned too much. Unlike apples and pears that respond well to pruning cuts, plums tend to sulk and are susceptible to diseases if they have too many wounds.

Arbury explains: “Many gardeners make the mistake of making too many pruning cuts and remove too many branches. This results in the tree putting on lots of reactive growth and producing little or no fruit."

He continues "Gardeners instead should not make too many cuts and only do so if the tree is crowded and casting too much shade or is outgrowing its space.”