How should I train a young walnut tree?

Training decides how your orchard starts to produce a crop. Either it has a sound canopy that you can harvest, or it has years of corrective work ahead of it. The canopy is the branches and leaves of the tree.

The objective is to establish:

• one leader (the main upright shoot at the top of the young tree)
• enough clearance for your machinery (enough free space under the lowest branches)
• strong attachments (strong joints between the branches and the trunk)
• a canopy that fits the orchard system.

Everything else is optional. That includes making every tree look identical.

If a cut does not solve a health, safety, access, structural or planned canopy problem, leave the wood.

Young walnuts respond to cuts. Heading (cutting off the end of a shoot, or the top of the young tree) concentrates growth below the cut. Thinning (removing a whole branch at its origin) removes a competing or badly placed branch without causing the same burst of replacement shoots.

Repeated heading therefore tends to create the regrowth that demands more pruning next year. In the first years after planting, keep the tree growing. Keep useful leaf area and fruiting wood (the shoots that carry the nuts). Make only the cuts that guide the permanent structure.

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Choose one training system, and stay with it

Young walnuts can be trained successfully under either of the two systems below. Pick one for each block and stay with it. Do not turn a no-heading block into a headed one because a few trees look untidy. Do not keep a defective leader to comply with a no-heading rule.

In this chapter, central leader means one dominant main trunk. Modified central leader is the minimum-pruning system. In this system, the trunk establishes the scaffold framework before the canopy broadens.

What the research shows

The evidence supports pruning lightly in young orchards. University of California trials looked at several lateral-bearing varieties, which produce nuts from side buds along the shoots, not only at the shoot tips.

The trials found that unheaded trees (trees whose tops were not cut) generally produced higher early yields. From about the fourth year onward, their yields were similar to those of minimally pruned trees. Heavily pruned trees were smaller and yielded less in the early years. A two-year study on Fernor likewise found higher cumulative yield (the total yield over the years) from unpruned, unheaded trees.

Routine heading is not a substitute for a training plan. The results do not mean that every variety, site, spacing or nursery tree should be left unheaded.

The same University of California work supports the answer on our Howard page. In an eight-year trial with hedgerow trees (trees planted close together and kept as a continuous hedge), trees came into bearing without annual pruning. The trial found no significant difference in height, nut quality or cumulative yield after eight years.

The decision is made at planting, not after

Heading the nursery tree when it goes into the ground commits the block to a headed, scaffold-based tree. You cannot decide in the second dormant season to run a no-heading block if the leader was cut to knee height at planting. The dormant season is the winter resting period of the trees, when they have no leaves. No leader is left to leave alone.

So choose the system before the trees arrive. Choose it together with three other things:

• the finished height and quality of the nursery tree you are buying
• the clearance that your harvester and mower need
• whether the block is standard-spaced (wide spacing, so that each tree has its own space) or a hedgerow.

If you settle those four one at a time, in the field, they will contradict each other.

Understand the wood before you cut

A thinning cut removes a branch at its origin, or back to a suitable lateral (a side branch). A heading cut removes the end of a shoot or branch. It usually makes several buds below the cut start to grow.

In young walnuts, head only where the system that you chose calls for it. Do not head a leader to solve a support problem. Use a stake instead. Do not shorten productive shoots because they look too long either.

Protect next year's fruiting wood

Walnut varieties differ in where they carry their crop, and the difference decides what a cut costs you.

Every variety that we produce, except Franquette, is lateral bearing. That is why heading matters more here than it does in a traditional orchard. The table below shows the bearing habit and the tree habit of each variety, as published on our own variety pages. The tree habit is the shape in which the tree grows.

Fernette is not listed separately because no distinct bearing habit is recorded for it. It closely resembles Fernor, and we grow it as Fernor’s pollenizer (a variety planted among the main variety to supply pollen). Chapter 3 covers what these habits mean when you first choose a variety.

Never tell a crew to shorten all the productive shoots. Decide first what each shoot is: fruiting wood, replacement wood, permanent framework, or an unwanted upright competitor. An upright competitor is a shoot that grows straight up and competes with the leader. These four types need four different answers. Only the last type is always cut.

Sometimes the variety record and what you see in the field disagree. In that case, it is almost always safer to leave a questionable shoot for another season than to remove next year’s crop positions on an assumption.

The no-heading system

Use no-heading only where the nursery tree has a sound scion leader. A scion leader is the leader that grows from the grafted variety, above the graft union. The graft union is the joint low on the trunk where the variety was grafted. Use no-heading only where you already know the trunk and clearance heights that the block needs. No-heading is not an instruction to leave a poor tree unchanged.

An unheaded tree builds its framework by growing longer at the tips (extension) and by growing side branches (lateral branching), not by repeated cuts. Individual shoots commonly alternate. In some years they extend strongly. In other years they make short side growth. The short years are part of the normal pattern. They are not evidence that the tree has stopped growing.

Your job is to preserve that pattern where it suits the block. Correct these problems before they become expensive:

• a double leader (equal main shoots that compete with each other)
• a weak fork (a narrow point where a stem divides)
• a real access problem.

At planting

A tree that suits no-heading has a sound leader, which is straight or can be corrected. It also has a healthy graft union, no serious transport damage, and enough leader height for the orchard system.

When the leader breaks, freezes or dies

Leader failure is a training problem with a deadline, because you must act in the same season. Do not treat it as damage that you can tidy up later.

Do not strip every small lateral and leaf from around an injury. Remove only the shoots that compete directly with the chosen leader or get in the way of training it. The remaining shoots and leaves help the tree to repair itself.

The first growing season

The aim is to have one healthy leader, protected trunk tissue, and no permanent double leader. Inspect the tree during active growth, and correct a competing upright shoot while it is still small enough to rub off.

Do not cut the tip off a sound leader to slow it down, and do not restrict water to slow the tree. If the support is the problem, extend the stake.

If growth is unusually strong or unusually weak, look for the cause in the block, not in the tree. Review irrigation, nitrogen, soil variation, crop load (the amount of crop that the tree carries), and root or disease problems before you use the secateurs. Chapters 6 and 8 cover the first two.

Staking, and when to take the stake away

A stake is temporary support, not part of the permanent tree. Check the ties after wind, and check them as the trunk expands. A tie has to hold the leader without rubbing it and without tightening around it. It must also not prevent the normal movement that builds trunk strength.

Sometimes the tree leans, the leader bends sharply, or the base of the tree moves in the wind. If this happens, tie the tree again, loosely. Then find the cause and fix it before you try again. The cause may be a weak trunk, a stake in the wrong place, wet soil, root damage or a canopy that is heavier on one side.

Never leave an unused tie around the trunk. You will find it years later, buried in the bark.

The first dormant season

Prune only once the local frost risk and the disease-weather assessment allow it. Then follow these steps in this order:

1. Keep the selected leader unheaded, if it is sound.
2. Remove upper laterals only where they compete with the leader, or where they are weakly attached and crowded above the planned scaffold zone.
3. Above the intended scaffold zone, rub off a problematic necked bud where a viable secondary bud sits below it. This favours the secondary bud and a wider crotch (the angle between branch and trunk). Do not remove every bud.
4. Extend or adjust the support if the leader cannot stay upright in the wind you expect.

Low, weak-growing laterals can be useful, because they shade the trunk and build caliper. Keep them only if they do not interfere with clearance, equipment or the dominance of the leader. The leader must stay the strongest shoot. Treat these laterals as temporary from the start, and decide now when they will come off.

The second and third seasons

Permanent clearance is about 1.2 to 1.5 m in standard-spaced orchards and 0.9 to 1.2 m in hedgerows. Those are starting points. Set the real height from the shaker (the machine that shakes the nuts loose), mower, sprayer and harvest equipment that you really use in the block. Chapter 4 covers which layout you are in.

At the second dormant-season pruning, remove branches below permanent clearance. A low branch can stay only if it meets all of these conditions:

• It is a weak-growing temporary branch, kept for shade or caliper.
• It does not interfere with equipment or the leader.
• It has a clear removal date.

Keep the leader and the permanent scaffolds unheaded. Remove a genuine narrow, included-bark fork (a narrow fork with bark trapped inside it) or an equal-strength upright competitor before it turns into a large defect. Do not remove normal wide-angled laterals only because they are not perfectly arranged.

By the third year, short side growth on an unheaded tree is likely to be part of its normal extension-and-branching pattern. On its own, short side growth does not indicate weak vigour, and it does not justify heading. Compare it against irrigation, nutrition, soil, crop load and the neighbouring trees before you cut anything.

At the third dormant-season pruning, remove only a branch that:

• blocks equipment or creates a safety problem
• is dead, broken or diagnosed as diseased
• is a structural defect that is likely to worsen
• sits below permanent clearance.

Do not head a scaffold because it made a long extension shoot. First decide what that shoot is: productive one-year-old wood, planned framework extension, or an unwanted upright.

The minimum-pruning system

The minimum-pruning system is the alternative: a modified central leader. A headed leader establishes the scaffold framework, and the canopy then develops around it. Use it where you have chosen a headed, scaffold-based tree and the crew knows the variety, the vigour, the spacing and the clearance height.

This system gives the tree the following shape:

• a leader of at least 2.1 to 2.4 m before heading in standard-spaced trees
• four to six primary scaffolds selected over the second and third years
• scaffolds distributed around the trunk rather than in opposite pairs.

In the early years, select the leader first, then select the scaffolds as they develop. Prefer branches that are well attached, well separated along the trunk, and spread around it.

Remove a competing fork early, while a small thinning cut still solves the problem. Do not wait until the tree carries two equal stems or a heavy, weakly attached limb. Leave useful small wood that is not crowded and is not in the way. It contributes to early canopy development and to early production.

Watch: the first pruning after planting

Almost everything above happens in the dormant season, because that is when the structural decisions are made. You should also inspect the tree during active growth and deal with a competing upright while it is still small. Most growers are least sure about this summer visit. It is hard to know how much to cut off when you are standing in front of the tree with the secateurs in your hand.

We filmed a young walnut being pruned for the first time after planting. This was the June work on a tree that went into the ground the previous November or March. It is usually called the first summer pruning.

Watch how little wood really comes off, and how specific each cut is. Nobody in that footage is tidying the tree up.

When training is finished

Training is complete when the tree has the structure that its orchard system needs, not when it reaches a particular age. The tree is ready to move from training to corrective pruning when it has all six of these:

Once the tree meets those conditions, stop trying to design the structure of the tree. From then on, prune for health, safety, machine access, disease, a structural defect that is likely to worsen, or a genuine problem with light or fruiting wood. Do not prune every tree because the block has reached a certain age.

Before the crew starts

When the crew should stop and ask

• The system for the block is unclear.
• A heading decision depends on a variety or bearing habit nobody is sure of.
• A leader repair could leave a permanent fork.
• A tree has no viable scion leader.
• The required clearance is not known.

A walk through the block before and after the work is usually enough to keep the plan working. Before pruning, look at several trees across the range of vigour and decide what a good finished tree looks like in this block.

After pruning, check that:

• the leader is still dominant
• the clearance matches the machinery
• every temporary low limb has a purpose
• no stake or tie is rubbing a trunk.

These two checks stop a sound system from being undone, one cut at a time.

Mistakes worth avoiding

• Heading a sound nursery tree when the chosen system is no-heading.
• Leaving a damaged, weak or too-short leader uncorrected to follow a no-heading rule.
• Treating a guide number as machinery clearance. Measure your own equipment.
• Allowing two equal leaders after leader damage.
• Tying a leader tightly, leaving an unused tie on the trunk, or removing support before the tree can stand alone.
• Treating all one-year-old shoots as shoots that you do not need, without checking the bearing habit and what each shoot is doing.
• Repeating a dormant heading cut to remove the regrowth that the previous heading cut created.
• Removing temporary low branches without deciding whether trunk shade or caliper support is still needed.
• Pruning on a fixed date without checking frost, weather, disease and field conditions.

If you are not sure which system your block should be in, ask us before the trees are planted.