The Macadamia tree (with few exceptions) has at each bud node a group of buds. I will use the terms "primary," "secondary" and "tertiary" to describe these nodes. Diagram #1 shows their position. Diagram #2 compares the bud sets of the two species integrifolia and tetraphylla. Note that integrifolia has three bud sets per node and tetraphylla, generally, has four per node. Hybrid varieties (genetic cross-pollinated seedlings of tetraphylla and integrifolia) have nodes that can vary from three to four nodes on connected limbs throughout the tree. Some may have more. Diagram #3 illustrates the spacing of nodes, which can, vary from as little as 1/4 inch (approx. 1 cm), to as much as 8 inches (approx. 20 cm) on rapid growing varieties. The average spacing between nodes is from 1 1/2 inches to 2 I/2 inches. Bud nodes can produce a leaf, a limb, or a fruit stem at any single node. This selectivity is random and complex within nature and the Macadamia species. As these primary, secondary, and tertiary buds emerge they form limbs at different angles (diagram #4). If "A" was the central leader at the top of the tree, all would be well, but if "A" were in competition with another "A" type, the tree would become a double-trunked tree with a very narrow angled crotch or a V-crotch (diagram #6). This narrow crotch has a major problem. As this limb or trunk grows in size, it has much more weight, and it is the weight that causes its ultimate failure or fracture. The crotch separation is caused with the tree's weight and wind. The small separation allows tissue dieback (a condition in woody plants in which peripheral parts are killed especially by parasites) and fungi entry (which causes further tissue dieback) to happen. In time you have a fault, much like an earthquake fault. A weakening of the basic trunk with one strong gust of wind can cause 50 to 75% of the tree to break off. This V-crotch is more apparent in integrifolia than in tetraphy11as and hybrids. The 'Cate' tetraphylla tree grown in California, in many cases has been sold to growers with either poor management advice or none. The poorly advised growers have left these trees to grow from the first division of foliage 18 inches above the ground line (see Fig. #7). This has caused undue weight and pressure as the trees approach 4 to 5 years of age. Splitting causes much structural damage to this variety. Shaping thereafter with pruning in many cases causes much deformation and many years are necessary to return the tree to a supportive and productive tree.

Diagram #5 shows the more desirable shape for a Macadamia tree. This desirable shape is defined as a central leader concept of scaffolding, and it has many " advantages. (1) The "B" and "C" limbs of diagram #4 establish the initial scaffolding which can support a heavier load or nut production. (2) These limbs can be tip-pruned to cause multiple limbs on their ultimate extensions. This will give more foliage to help achieve maximum production. As the tree grows in height and age, this shaping is encouraged. As the tree becomes mature with the central leader pattern in place, it will have a combination of good production and good support for the crop. This training will produce a more ideal shape that will resist the ravages of strong winds with possibly only a few small limbs breaking. If you allow the tree to assert itself as a young grafted tree without shaping you can end up with a real mess in structuring. I try to train my trees up to 1 1/2-meter (4 ft.-4 1/2 ft.) height before I let them divide and create the basic scaffolding. If they do not divide at this height, I pinch the terminal bud or tip bud, which will cause the tree to grow three or four new limbs during the next flush of growth. I have observed trees where no pruning was done and the tree limbs touch the ground. If the primary purpose of the tree is for appearance, then this is fine, but if this were allowed to occur in an orchard, the grower would eventually hate his decision not to prune. He would be crawling around on his hands and knees, under the low limbs, looking for the nuts. Also, falling leaves would collect under the skirt, which would be difficult to rake out because of the low limbs, and would make finding the nuts difficult, it would encourage insect infestations to develop. Diagram #7 shows the structure of the popular "Cate"variety here in California, which is described as an umbrella shaped Macadamia tree. This Macadamia tree has a mind of its own as well as a shape of its own. It is impractical to try to train "Cate" to a central leader shape because it won't cooperate. The illustration reveals its four-main-limb character. Each limb then divides into four smaller limbs. It has little of the V-crotch character. The most important training point to make for "Cate" is that you maintain its trunk to one single trunk until the tree is ready to establish the basic scaffold (about 4 ft.-5 ft. above the ground). Then, let it form its four-limb character. If you don't maintain one trunk, you will have a multiple-trunked tree close to the ground. The "Cate" should be thinned out in the center for better light entry, however too much inside thinning exposes the tree to sunburn. Also, "Cate," when adult, has a large open-umbrella shape which offers a large mass to prevailing winds. The danger here is from heavy rains followed by powerful winds which easily cause "wind throw" (trees blown down by heavy winds).

I have heard of a new method of pruning in Australia, but as yet have not seen it or any photos of the technique. I am told it is an espalier technique very similar to grapevines or decorative plants. I have found one reference to espalier in macadamias: 1984 CMS Yearbook, pg. 96 "Trochoulias (personal communication) has found that Macadamia is very difficult to train to given branch angles such as those in espaliers, etc. and have given poor yield responses to such training methods." This technique exposes much more area to sunburn because of the more open trunk and limb areas. Sunburn of Macadamia in California is quite prevalent and causes much set-back of growth in these trees, particularly young trees in the orchard. There are different methods (or experiments) to achieve better production on the Macadamia tree. I have heard of hydraulic-operated mower arms, which mow the trees in rows to shape, much like lemons are size-controlled. This would induce much division of new foliage on the exterior of the areas pruned, and theoretically induce more fruiting wood, but it could also induce more covered canopy and possibly reduce the light entry which is necessary to good production. A better approach is two-fold. (1) Regular elimination on the inside of the canopy of dead or dying limbs, keeping the tree active in the production of new wood. (2) It is useful to perform regular pruning of some inner limbs throughout the tree, particularly those which hang down. Excessive foliage or dense foliage throughout the tree causes another problem, that being insufficient light and air or ventilation to the tree. This can offer safe hiding to pests, insects and rodents. It will reduce production as insect pollination is more difficult, particularly bees entry and easy passage to the flowers. Diagram #8: "X" represents limbs that could be removed if dead. Diagram #9: "X" represents limb removal to induce new limb formation for later production. I feel that it is very important to maintain a regular patrol and removal of this dead limb material. I have observed some trees so badly affected in this way from lack of care, that the only part of the tree that was growing was the extreme six inches of the exterior leaf area.

Pruning Instructions for the Pre-graft Period

The tree must obtain a trunk diameter of 1/4 inch to 5/8 inch which is the best size for grafting; this dimension to occur about
mid-height on the tree trunk, Select best emerging new growth.

 

(1) Remove all other new growth using a sharp knife or pruning shears. This must be done every 90-120 days. The object here is to train the seedling tree to have a tall, straight trunk with no side growth. (2) Remove new side growth or limbs as they form. (3) Prune suckers or new competitive trunks.

Pruning Recently Grafted Young Trees
 

It is imperative that you adhere to all instructions to achieve best results once your tree has been "field grafted." The buds will emerge within 20 to 90 days (weather conditions being favorable), and form new leaves. Patience here is necessary, as grafts have taken as long as one year to emerge! These new leaves will need up to 60 more days to fully form and "harden off." "Harden off" defines a tough, fully shaped, usually dark green leaf with a somewhat shiny gloss. (A) Sets of buds, which will form new leaves. (B) Scion grafted on seedling tree. (C) Graft and grafting tape. (D) New leaves, limbs, and sucker shoots at ground line emerging from buds below the graft must be removed regularly to insure that the energy will be pushed to the new scion. If you do not do this, chances are that all growth will happen below the graft, and the new graft will not take.

"Scion" is a section of a limb of a tree, which is usually an identified variety. It transfers the character of that tree to the seedling when the union forms and new growth appears. "Graft" is where the incision is made on the seedling tree and the piece of scionwood inserted, then taped, and then sealed with paraffin or tree seal or some other pliant substance. Water regularly. Do not spray with herbicides at this time especially ROUNDUP as this causes a witch-broom effect on the Macadamia. Its appearance is denoted by a profusion of buds on the bud node instead of a single one and new leaves do not fully form. Remove grafting tape when the first set of leaves on the graft has hardened off, usually near 60 days later. If you do not do this, damage could occur by the constriction of the new growth under the tape, that causing a weak fault and breaking later as the tree has more foliage above the graft. Do not use TANGLE FOOT to control ants and other climbing insects. It will kill the tissue on young Macadamia trees where applied, and could possibly kill the tree.

Pruning a Young Grafted Tree

Little pruning is necessary during the first year of growth after grafting. You should encourage all growth above the union at this time. (1) New graft. (2) Graft union. Carefully cut the grafting tape with a sharp knife but do not remove from the trunk, let this tape fall off of its own volition. This prevents rapid drying of the graft union, and shrinkage causing the scion to fall off. The tape should not be removed before the tree initiates a second set of new leaf growth. To encourage growth above the union, remove the leaves of the seedling which are no longer necessary to the tree.

After removal of the tape, be sure to paint the total exposed tree trunk with white latex paint (either interior or exterior. This will provide sunburn protection, to the tree. This protection process should be continued every year until the young tree fully canopies and protects itself from the sun.  If your graft is below four feet, you will have to keep heading up the main grafted trunk at least to that height or you will have a hedge instead of a tree. Select the strongest, vertically straight leader and remove all others, if the tree does not assert a natural division at the proper scaffold height, pinch off the terminal tip. Then a division will usually occur at the first set of bud nodes below the pinch/cut.  Four feet is reasonable to allow proper training of the tree for servicing, mowing, weeding, and harvesting. Young trees, leaving a nursery should be sprayed with an anti-transpirant. Forever Green, produced by Safer Chemical Co and Anti-Stress 2000 by Polymer AG are two good anti-transpirants. This same chemical can be used as a winter frost/freeze protectant.

Prune for Shape and Wind Resistant Structure

Macadamias are brittle,especially tetraphylla varieties. Many times tetraphylla varieties will form four long, whip-like trunks. You need to train the tree to one central, upright leader, then prune the other three to cause division which will form the canopy. Additional pruning at a later date probably will be necessary to further shape tetraphylla.
Integrifolia and hybrid varieties are more readily trained to a central leader concept.

 

(A) Remove long, whip-like branches.  Prune here. (B) Occasional pinching off of tip buds will form divisions of new growth, which will increase fruiting potential. (C) Encourage central leader which is the best support against wind. (D) Remove dead branches. (E) Tie Tape and Stake. (F) Wire brace; bolt. Limbs can be bolted together with suitably sized bolts.Branches with narrow "V" crotches may need tie-tape support, or removal, as strong winds will remove them.

If tree trunk is older and leaning, it may be necessary to provide support by inarch grafting.
Young trees can easily be stake-trained for upright growth. Be sure to place the stake at least three feet from the tree. Never put stakes directly alongside of the trunk and tie the tree securely to it as this causes three possible problems. First, the stake may sever the main root system and severely set the trees growth back many months. Second, closely tied stakes rub the bark from a young tree causing further damage and setback, and, finally, staked trees do not allow a natural movement of the tree in wind which releases a chemical that causes hardening of the structural wood tissue, therefore giving proper support.
Pyramidal or columnar tree shapes will be the trees of the future as their shapes are resistant to wind problems, give better production due to the openness and light entry, and elimination of some pruning.