How and when to prune a walnut tree

A walnut is the nut of any tree of the genus Juglans (Family Juglandaceae), particularly the Persian or English walnut, Juglans regia. A walnut is the edible seed of a drupe, and thus not a true botanical nut. It is commonly consumed as a nut. There are several species within this family, perhaps the most widespread and popular are English walnut and black walnut. In this article we will cover everything about how and when to prune a walnut, in addition we will analyze the features of English walnut and black walnut pruning.

If you read to the end you will learn the best techniques for proper pruning, the right time to trim and the tools to do it. The article has no waste, I assure you. 😉

1. Interesting fats about walnuts trees

Before entering the main topic of this post, prune the walnuts, I leave some interesting facts about this tree. I bet what you want, you do not know one or several of them. 😉

• Walnut is known as “karyon” in Greek language, which means “head”. Name originates from the fact that walnut shell looks like a skull which protects brain-like kernel located beneath it.

• The nuts that are not yet ripe contain cyanide, which is why it is not advisable to consume them. This is, also, the reason why it is repeatedly recommended not to sleep under the shade of the walnut tree. There are, in this regard, multiple proverbs.

• Hundreds of healing and medical properties have been granted to the walnut, although not all are true or proven.

• Although its goodness in the cardiovascular system seems to be demonstrated, its great contribution of calories (fats and carbohydrates) must be taken into account. You should, therefore, limit your consumption if you do not want to gain weight at the same time.

• Always, from very remote times, the nut has been associated with good health and memory.

• Walnut shells are used in the production of grit paper, glues, plastics and cleaning products. Walnut wood is used for the manufacture of flooring, furniture, musical instruments, panels, veneers and gunstocks.

• In ancient Rome, if the groom threw nuts to the crowd, he meant that he would be faithful to only one woman.

• In times when tobacco was scarce, walnut leaves, once dried and chopped, were used as their substitute.

Until here some of the curiosities that I have considered more interesting about the walnut. Now let’s do our thing, pruning. 😉

2. Tools needed to prune or trim a walnut tree

As with all fruits, there are several tools you will need to carry out your pruning or trimming. Each of them appropriate for different cases depending on the age of the pomegranate, the time of year, type of pruning etc.

• Pruning shears.

• Handsaw

• Chainsaw.

• Ladder or scaffolding.

• Basic safety elements such as helmet and gloves.

Keep in mind that you must disinfect all cutting tools before pruning the walnut tree. This will help to avoid transmitting diseases, you will have to do it before you start pruning and every time you change plants.

2.1 Needed care of pruning tools

If you want to extend the useful life of your pruning tools there are some basic care.

• Use the right tool for a job and avoid twisting or straining it.

• Clean and oil tools regularly by wiping an oily cloth on blades and other surfaces.

• Keep cutting edges sharp by regularly using an oilstone.

• Wooden handles should be varnished or regularly treated with linseed oil to keep them from cracking or splintering.

Carry out the previous care on a regular basis and you will be saving good money on tools. 🙂

3. Pruning a walnut tree – How to prune

The pruning of the walnut can be divided into three, depending on the age of the garden and the objective that is sought with pruning. These are training pruning, production pruning, corrective pruning, rejuvenetion pruning and topping.

• Training pruning: this pruning is done from the plantation until the sixth to seventh year, and aims to drive the plant and generate a productive structure that is efficient as quickly as possible.

• Production pruning: this pruning is done since the productive structure is formed, in some cases from the sixth year onwards and aims to keep the garden well lit to achieve high production and not lose productive centers in the tree for lack of light.

• Corrective pruning: this pruning aims to correct problems that reduce the productive potential of the garden and aims to modify the structure as soon as possible to increase the productive efficiency of the tree. The main problems are the shade and the concentration of main branches in the lower part of the tree, which generates an insufficient height of the productive structure.

• Pruning of renewal: when the walnut trees reach their age (about 10 years old) they need to renew their branches, this is achieved with a more severe pruning than the previous ones, which is known as pruning of renewal.

• Topping: It consists of selectively removing the upper branches or the central leader of the tree. It is usually something done on walnut trees that have grown too tall. As it is pruning at height, it is something that I always recommend that it be carried out by professionals. If you happen to live in or near Knoxville you can request Mencer’s Tree Service.

Since each of the previous prunings are very different, both in objectives and in techniques, we will then separately develop each of them.

3.1 Training pruning – Prune young walnut trees

There are numerous factors that influence the pruning of formation of a walnut tree, among them we can mention:}

• Objective of the plant: the most determining factor when forming a walnut tree is determined by the purpose for which we plant this tree. The most common is for the production of nuts but it is also widely used for wood production.

• Variety: depending on the characteristics of the variety of walnut that is being used, the pruning of formation varies.

• Vigor of the trees: If there is a lot of vigor it is necessary to control the lack of light in the center of the plant from the third year, if the vigor is too low it is necessary to make cuts to induce vigorous growths.

• Wind: in places where the wind is a serious problem, it is necessary to take certain precautions. The trunk should not be cleaned more than what is needed for good weed control, to achieve a more compact tree with a more resistant trunk, which considerably reduces the problems with the wind. You also have to consider a good tutor to achieve a well-formed plant.

• Light: when the walnut is being formed, it is necessary to consider the best possible use of light, which is essential for good production. For this reason, the structure must be efficient. A maximum height must be considered so that the shade of one tree does not harm the production of the other, the height of the plant must not exceed 80% of the distance between rows, also within the same tree it is necessary to achieve a good distribution of the branches so they do not shadow each other.

Since this walnut pruning is governed by many factors it is difficult to cover all the possibilities in a single article. In the same way we can summarize the training pruning in two types; Training pruning for nut production or walnut formation for wood production.

3.1.1 Training pruning for nut production

The pruning of a walnut to produce nuts begins in the plantation. The shape to which this plant best adapts is that of the one developed with a central axis.

It consists of forming a main trunk – the axis – that grows in height as the tree develops, and some main branches of horizontal growth that are selected along the trunk so that there is space between them – but not too much – and that they are oriented alternately in all directions, to form a consistent cup.

For this, in summer the most vertical and most vigorous growth bud is chosen, and a tutor is tied to keep it straight. The other shoots are blunted since they will then be cut in winter. In the following summer, the branches that have not been selected as main ones are highlighted, and those that still are, grow disproportionately. Those that compete with the axis in vertical growth will be eliminated.

While the formation lasts, it will be necessary to cut the axis in winter about 50 cm above the last main branches, to form a new floor of branches below this point, which will have to be selected again to leave the best orientations and eliminate those that can compete with the axis.

3.1.2 Training pruning for wood production

In the case of the formation of a walnut to produce wood what we are looking for is to develop a main trunk as straight and without knots as possible. For this, a dynamic or balanced pruning scheme can be developed.

3.1.2.1 Dynamic training pruning

Dynamic pruning in the formation of walnut is recommended in sheltered and fertile farms. It does not set pruning height. The first two years all branches are pruned.

The following years the lower branches are eliminated, hairpins are corrected and the cup is balanced horizontally. In 7 years you can reach 3 m free of branches.

3.1.2.2 Balanced training pruning

This second trained pruning called as balanced is recommended in most farms. In this case, a pruning height (H) is set according to the quality of the farm (between 3 and 6 m). Until the tree reaches height H, it is especially monitored that there are no forks or branches that can compete with the main trunk for dominance.

The branches of the year that have acute insertion are eliminated and compete with the terminal guide, in particular the forks. Also the branches of a year or more that approach 2.5 – 3 cm or that present acute insertion. Finally you can cut the branches that can reach this thickness shortly.

After reaching height H, the objective is to progressively clean the trunk of branches. To avoid breakage, it is convenient that the tree does not open immediately after reaching H.

3.2 Production pruning

With this pruning of the walnut tree should be kept illuminated throughout its structure. It is necessary to eliminate the growth of new times that generate problems, renew the production centers to produce the pieces of good quality and it is also necessary to maintain a structure that allows the realization of the work of cultivation in the garden. For this, we recommend that you perform the following activities, ordered by their priority.

• Light inside the tree: in order to keep the tree well lit, it is recommended to allow light to enter from the north, eliminating the branches that obstruct the entry of light, in the form of a triangle towards the center of the plant.

• Elimination of badly located branches: It is necessary to eliminate branches that are close together where shading occurs, to maintain a good use of light.

• Elimination of badly located pacifiers: It is necessary to eliminate every year the suckers that are inclined towards the center of the plant and also those that are in an upright position, because this position produces a greater shade and with the weight they can be tilted towards the center of the plant.

• Light between rows: to achieve this goal, it is necessary to define a minimum distance between the rows free of branches and cut branches every year that exceed that limit.

• Renovation of production centers: when a walnut is pruned it is necessary to review the branches year after year. In the case that it is observed that the greater proportion of the darts are too short (<5 centimeters), it is convenient to eliminate the branch since the production is limited and the quality of the nuts is not good in relation to the caliber.

Taking the previous precautions during the production pruning of the walnut will ensure a higher quality of nuts for the harvest.

3.3 Corrective pruning of the walnut

In pruning correction there are several examples. We will mention the most important ones and their alternative of correction.

3.3.1 Ambush

This problem occurs in plantations that are left without light inside. This has as a consequence that the production moves to the periphery and the roof of the orchard, decreasing notably the production of nuts per hectare.

The solution is to let the light into the garden, the first step is to open the inter row and then the following year it is necessary to facilitate the entry of the light in the north-west zone of the tree and in a third year to select the branches that are badly located. The solution to this problem takes 3 years.

3.3.2 Low altitude garden

This problem is generated when in the formation too many main branches are left in the lower part of the tree (5 to 6 branches between 1.6 to 2.6 meters), which generates a low tree, where the central axis has smaller diameter than the basal branches.

You will imagine that we will give solution with a pruning in the walnut. With this pruning we will have to transfer the vigor to the top of the tree, and this is done by removing one to two main branches from the bottom of the tree per year until leaving two to three at most between 1.6 and 2.6 meters. The diameters of the main branches must be less than 1/3 of the diameter of the central axis.

3.4 Pruning of renewal – Prune old walnut trees

After a certain age (about 10 years) the walnut will need to be renewed as its branches begin to be unproductive. When that happens it is the right time for a pruning of renovation in the walnut.

The pruning of renovation consists of eliminating the non-productive wood of the plant, with the aim of generating new production centers. This pruning could be carried out in a season, but this brings as a consequence a sudden fall in production. That is why it is recommended to make cuts in a staggered way during the successive seasons, lowering the thick branches, so that the yield does not fall sharply.

In the first year the lower branches are cut, the second the unproductive ones, and in the third year the upper ones, which generate excess shade. This prevents the production of the garden from going down a lot. What is eliminated the previous year is recovered in the following season.

3.5 Topping a Walnut Tree

As we already mentioned, topping is to selectively remove the upper branches or the central leader of the tree. Topping a walnut tree can be beneficial in certain situations, but requires careful consideration and proper technique to ensure optimal results. For this reason and because it is generally pruning at heights, I have recommended that you call a professional to top your walnut tree.

The topping of a walnut is generally done for specific purposes, among the most prominent we can mention:

• Control the height of the tree.

• Control your size.

• Rejuvenate old or abandoned trees.

• By controlling the height it makes maintenance or harvesting tasks more manageable.

• Lateral growth is encouraged.

• Fuller crowns are achieved, enhancing fruit production.

It seems that all are benefits with topping, but if you do it incorrectly, the problems will be greater. Drastic or improper topping can place significant stress on the tree, affecting its overall health and productivity. Therefore, it is crucial to follow proper pruning guidelines and consult with experienced arborists or horticulturists before pruning.

When topping a walnut tree, several considerations must be taken into account.

• It is crucial to top at the right time. It is best to do this during the dormant season, preferably in late winter or early spring. By doing this before new growth begins, you allow the tree to recover and heal more efficiently.

• The branches to be removed must be carefully selected. You should look for branches that are structurally weak, those that are damaged or that interfere with the overall shape of the tree. Removing large, healthy branches should be avoided, as this can upset the balance of the tree.

• When cutting, clean angled cuts should be made just outside the branch collar. The angle will allow water not to accumulate on the cut, avoiding the appearance of fungus.

• It is very important to use sharp and disinfected pruning tools. In this way you help minimize damage and the risk of disease transmission.

• It is best to prune gradually. Instead of removing a significant portion of the tree canopy at one time, you can do it in several scheduled prunings. This way you can reduce stress and promote healthier growth.

Once the topping of your walnut tree is finished, it is essential to carry out post-pruning care. You can cover the cuts of the branches with healing paste, this will prevent the appearance of pests or diseases. It is also good to apply a good irrigation and some fertilizer. These small cares seek to reduce the stress of the tree and facilitate its recovery.

4. When to prune walnut trees

The selection of the right time to prune a walnut comes from the hand with which it is a deciduous tree, meaning that it loses its leaves during the winter. Because of this, the ideal time to cut branches is winter.

When the walnut is at rest during the winter months there will be less loss of sap in the cuts, thus reducing the level of suffering of the same, allowing a faster recovery. In general, and as far as possible, it is to winter meditations when it is recommended to prune the walnut. If you prune very early you are more likely to acquire diseases through the cuts, and if we can very late there will be greater loss of wisdom and therefore energy.

So you know before you start pruning this plant, look at the calendar, if you’re in mid-winter, it’s time to work. 😉

5. Pruning black walnut trees

There are many questions about how to prune a black walnut tree. That is why I found it interesting to devote a small section to answering this query.

The pruning of a black walnut does not have great secrets, having to carry out the same pruning as in a common walnut tree. This is training pruning, production pruning, corrective pruning and renewal. If you follow the advice we have seen so far in this article, you will not have any problems carrying out this afternoon in your black walnut.

6. Pruning walnut trees video – YouTube

As we always do in this blog we will finish this article with a video, although on this occasion I have selected more than one. In the first video we talk about the pruning of training in a walnut tree.

In the second video you will see the mechanized pruning of walnuts.

Well that has been all, I hope that it has been clear that I have seen them until now, how and when to carry out the pruning of a walnut tree, and that you have no doubts when you take your scissors and start trimming. 😉

Source information:

Estrategia de poda en nogales – http://www.chilenut.cl

Nogal para madera – Óscar Cisneros, Víctor Martínez, Gregorio Montero, Rafael Alonso, Antonio Turrientes, Javier Ligos, José Santana, Raúl Llorente y Eloy Vaquero.

Aspectos técnicos para la poda del nogal – Giovanni Lobos L., Ingeniero Agrónomo, INIA Intihuasi