Why Plum Trees Grow Too Tall and the Risks
A plum tree's vigour can sometimes lead to excessive height, making it difficult to manage, harvest, or treat for pests and diseases. Understanding why this happens is the first step to effective control. Often, overly vigorous growth, particularly in younger trees or certain varieties, can result in a sprawling canopy that reaches skyward rather than outwards. This can be exacerbated by excessive nitrogen in the soil or insufficient pruning in previous years, which encourages upward, vegetative growth over fruit production.
The primary risks associated with a plum tree that is too tall include reduced fruit quality and yield. Higher branches receive less light, and developing fruit may struggle to ripen properly. More critically, access for pruning, spraying, and especially harvesting becomes hazardous. Attempting to reach high branches without proper equipment or technique can lead to falls and injuries. Furthermore, dense, tall canopies can become breeding grounds for fungal diseases due to poor air circulation and prolonged leaf wetness.
You might also find that pruning a tree that has already become unwieldy is more challenging. It's easier to maintain a desired size from the outset than to drastically reduce a mature, overgrown specimen. Ignoring the height can also lead to weaker branches that are more susceptible to breakage from wind or heavy fruit loads. A tree that is too tall is simply less productive and more problematic.
Common Pruning Mistakes to Avoid
Several common errors can worsen the problem of an overly tall plum tree or damage the tree during attempts to correct it. One significant mistake is removing too much of the canopy in a single pruning session. This can shock the tree, leading to a surge of new, vigorous, upright growth (water sprouts) which negates the effort and can make the tree even taller and bushier in the long run. Another error is pruning at the wrong time of year. While plums are typically pruned in late spring or early summer after fruiting, drastic height reduction is often best undertaken in late winter or early spring when the tree is dormant, allowing it to heal more effectively before the growing season. However, this needs careful consideration to avoid damaging blossoms.
A frequent oversight is the type of cut made. Topping the tree – simply cutting off the main leader or large branches indiscriminately – is highly detrimental. It removes fruiting wood, encourages weak, vertical regrowth, and creates large wounds that are slow to heal and prone to disease. Instead, cuts should be made back to a lateral branch or a bud pointing in the desired direction, maintaining the tree's natural structure where possible. Using dull or dirty tools is another common, though less obvious, mistake. These tools can tear the bark, crush vascular tissue, and spread diseases, compromising the tree's health and healing ability.
Addressing an overgrown plum tree requires patience and a structured approach to avoid causing more harm than good.
Finally, a significant error is not having a clear objective. Are you trying to reduce height, improve light penetration, increase fruit yield, or make harvesting easier? Without a defined goal, pruning can become haphazard. For instance, simply cutting off the top few feet without considering the tree's overall structure or future growth can lead to a 'lollipop' effect with bare branches and a dense crown at the very top, which is neither aesthetically pleasing nor productive.
Techniques for Reducing Plum Tree Height
When your plum tree is too tall, the goal is to reduce its vertical growth while encouraging a more manageable, productive structure. This isn't about simply hacking off the top; it's a strategic process. The most effective method for height reduction involves identifying the main vertical leaders and cutting them back to a suitable lateral branch that is growing outwards or downwards. This redirects the tree's energy into developing a more horizontal or bushier habit rather than continuing to grow upwards. Always select a lateral branch that is at least one-third the diameter of the branch you are cutting off to ensure it can support the load and continue to grow vigorously.
Strategic Cuts for Height Management
Begin by assessing the tree's overall shape and identifying the branches that contribute most to its excessive height. You'll want to make cuts just outside the branch collar – the swollen area where the branch joins a larger limb or the trunk. Avoid leaving stubs, as these are entry points for disease and will often produce weak, unproductive water sprouts. For very tall trees, this process may need to be spread over two to three years to avoid stressing the tree. In the first year, tackle the uppermost branches, cutting them back to strong, well-placed lateral branches. This begins the process of lowering the canopy.
Consider using a pruning saw for branches thicker than a finger. For very large branches, support them with a rope while cutting to prevent them from tearing bark down the trunk as they fall. When cutting back a leader, choose a lateral branch that is growing at a roughly 45-degree angle away from the original leader's direction. This helps maintain the tree's balance and light exposure. If no suitable lateral branches exist, you might need to cut back to a strong bud, angling the cut to drain away from the bud. However, this method is less ideal than cutting to a lateral.
Always use sharp, clean pruning tools. For high branches, consider using long-reach loppers or a pruning saw on an extension pole to avoid the need for unstable ladders and to make cleaner cuts.
Timing Your Pruning Efforts
The best time to undertake significant height reduction on a plum tree is during its dormant season, typically in late winter or early spring before new growth begins. Pruning in dormancy minimises sap loss and reduces the risk of disease infection entering fresh wounds. It also allows you to see the tree's structure clearly. However, if you've pruned heavily, you might see a flush of water sprouts. If these grow in undesirable locations, they can be removed during the summer pruning session, which is typically done after the main fruit harvest to remove unproductive wood and improve air circulation.
Avoid heavy pruning when the tree is stressed, such as during a drought or extreme heat. If the tree is suffering from disease, it's often best to delay major structural pruning until its health improves. For routine maintenance after height reduction, annual pruning in summer is recommended to maintain the desired size and shape, remove any dead or diseased wood, and encourage fruit production on younger wood.
Restructuring for Future Growth and Fruit Yield
After reducing the height of your plum tree, the focus shifts to restructuring its canopy for better future growth and improved fruit production. The aim is to create a more open, goblet-shaped or vase-like structure, which allows sunlight and air to penetrate the entire tree. This is crucial for the development of sweet, well-ripened fruit and helps prevent diseases by reducing dampness within the canopy. By strategically removing inward-growing branches, crossing branches, and any remaining upright shoots (water sprouts) that arise from your reduction cuts, you encourage the tree to spread outwards.
Encouraging Fruit Production
Plum trees primarily fruit on spurs, which are short, stubby growths that typically form on two- to three-year-old wood. By pruning to maintain a balance between fruiting wood and vegetative growth, you ensure a consistent supply of fruit. After significant height reduction, the tree might spend a season or two re-establishing its fruiting capacity. Summer pruning, after harvest, is key here. It involves removing weaker shoots and thinning out overly dense areas to expose existing spurs to light. This also prevents the tree from putting all its energy into producing new, tall shoots.
When pruning, always make cuts back to a lateral branch or a bud. This encourages new growth in the direction you want it to go. For example, if you cut a leader back to a lateral branch, the lateral branch will grow stronger and start to take over as a new leader, but at a lower height. This technique helps to rebuild the canopy structure at a more accessible level. Inspect the tree annually for any signs of plum tree diseases, such as bacterial canker or silver leaf, and remove affected branches promptly. Making clean cuts and pruning at the right time of year are your best defences.
After making major cuts, consider applying a thin layer of horticultural sealant to large wounds (over 2cm in diameter) to protect against disease, especially if pruning during wet periods, though opinions vary on the necessity for fruit trees.
Maintaining a Manageable Size
The long-term management of a plum tree involves regular pruning. Once you have successfully reduced its height and established a more desirable shape, annual pruning during the summer months is essential. This summer prune should focus on removing any vigorous upright shoots (water sprouts) that inevitably emerge, especially from cuts made on the main leaders. It also involves thinning out crowded areas and removing any branches that are growing inwards or crossing others. This maintains the open structure, keeps the tree at a manageable height, and promotes better air circulation and light penetration.
By consistently addressing any upward growth and maintaining an open centre, you prevent the tree from becoming too tall again. The goal is to have a tree where you can easily reach most of the fruit from the ground or with a small stepladder, making harvesting a pleasure rather than a chore. If you find yourself consistently battling excessive height, consider if the variety of plum you have is known for vigorous growth. In some cases, a different variety might be more suited to your garden space. However, with diligent pruning, most plum trees can be kept at a manageable size.
When to Prune Other Fruit Trees
While this guide focuses on plum trees, understanding when to prune other common fruit trees can help manage your garden holistically. For instance, when do you prune apple trees? Apple trees are typically pruned during the dormant season, in late winter or early spring, similar to plums, to encourage fruiting and maintain structure. This timing allows the tree to heal before the growing season and avoids removing potential blossom buds. However, a light trim to remove dead or diseased wood can be done at any time.
Pruning fruiting cherry trees is often best done in summer, after the fruit has been harvested. This is because cherry trees are more susceptible to bacterial canker and silver leaf disease, and pruning them in summer, when the tree is actively growing and the weather is drier, minimises the risk of infection. Summer pruning also helps to keep cherry trees more compact, as they can be quite vigorous growers. This contrasts with apples and plums, where winter pruning is generally preferred for structural work.
Understanding Blossom and Growth Cycles
The timing for pruning is intrinsically linked to the tree's flowering and fruiting cycle. For example, when do apple trees blossom? Apple trees typically blossom in spring. Pruning them in late winter ensures that you don't remove the wood that will bear those blossoms. Conversely, if you prune a cherry tree in winter, you risk cutting off the flower buds that have already formed on last year's growth, thus reducing that year's fruit yield.
The question of how big do cherry trees grow varies significantly by variety, but they can become substantial trees if not managed. Similarly, a quince shrub or tree, while often smaller, also benefits from annual pruning to maintain shape and productivity. Quinces are usually pruned in late winter or early spring. Understanding these different needs ensures that each type of fruit tree receives the appropriate care to maximise its yield and health, preventing issues like excessive height or disease from taking hold, much like managing your plum tree.