PRUNING
The almond trees normally set a larger number of fruit buds than they are capable of maturing. The number of blossoms set on a healthy tree to produce a full crop will be generally not more than 20 per cent of the total number which opened in the spring, and oftentimes much less. It has frequently been noted that trees which are somewhat lacking in vigor are inclined to set a larger number of fruit buds than those that are strong and vigorous. The normal set of blossoms on a young, vigorous tree is shown in [figure 2]. The result is that with the sub-normal strength of such trees being distributed among the extra number of fruit buds, the latter are not able to develop into the strong, healthy buds they should. The results of such conditions have been discussed on [pages 23, bottom, and 24, top]. One of the best means of securing and keeping healthy, productive trees is by careful, thoughtful and systematic pruning. The treatment given most of the almond orchards would indicate that the growers consider pruning to be one of the least important of the cultural practices.
Fig. 8.—Typical Drake almond tree in University Farm orchard; nine years old.
Fig. 9.—Typical Languedoc almond tree in University Farm orchard; nine years old.
To be most effective, pruning must be followed systematically throughout the entire life of the tree. The details of the practice will vary greatly, depending on the soil, moisture and climatic conditions surrounding the tree, as well as other treatment accorded it. At planting time, it is generally agreed that the tree should be cut back to between 18 and 24 inches from the ground to reduce the top to correspond to the shortened root system and to form a low head for the tree. A low head is desirable to avoid sunburn of the trunk and to keep the tree within easy reach for pruning, spraying and harvesting. During the first summer in the orchard much can be done to obtain a well-balanced head, to get the main branches well spaced on the trunk, and to prevent crowding later on, by pinching out all undesirable growth as fast as it appears and forcing the growth into those parts of the tree which are to remain. If these branches tend to grow too long and willowy, they may be made to branch by pinching back when they attain the desired height. In this way, if the tree can be kept growing vigorously, the beginning of an excellent foundation framework may be developed the first year.
Fig. 10.—Typical Nonpareil almond tree in University Farm orchard; nine years old. Note numerous water sprouts which must be removed.
Fig. 11.—Typical I.X.L. almond tree in University Farm orchard; nine years old.
The following winter, when the tree is one year old in the orchard, if it has grown too vigorously and the branches are too long and willowy and not properly branched it should be headed back to improve the shape and symmetry of the whole tree. If the tree has not made sufficient growth to give it a properly shaped head, it should also be cut back even more severely than in the case of the too vigorous growth. There sometimes will be trees that during the first year will develop such a well-shaped and stocky frame that no further heading will be necessary, all future pruning being limited to thinning out undesirable and interfering branches. Ordinarily, however, it will be highly desirable or necessary to continue the practice of heading-in the yearling tree at least. As long as heading continues it will pay to give special attention to pinching and thinning the following summer. In this way the frame of the tree may be developed more quickly and the future necessity of heading be materially lessened. In rich bottom lands where moisture is plentiful, heading may be necessary when the tree is two, three and, in extreme cases, 4 years old, in order to spread the tree and prevent it from growing too high. The necessity for this can only be determined by a careful study of the tree itself and the conditions surrounding it.
Fig. 12.—Typical Ne Plus Ultra almond tree in University Farm orchard; nine years old.
The habit of growth of a given variety will have a great deal to do with the number of seasons during which heading back will be practiced. Spreading varieties, such as the Drake (see [figure 8]), if making a strong, vigorous growth, should not be headed any longer than is necessary to start a sufficient number of main branches. Every opportunity must be given the trees of this variety to grow as upright as possible. Summer pruning of the drooping, undesirable branches wherever they develop, will help to increase the growth of the upright branches. By pruning as far as possible to inside buds, every opportunity will be given the trees to grow upward. If trees of such varieties make a poor, weak growth, a very heavy heading will force them to make a stronger and more vigorous growth the following season, provided any unfavorable soil and moisture conditions are corrected. Care must be exercised with these trees to prevent the downward growth of any of the branches by pruning them off during the summer, as suggested above. As soon as a strong, upright growth is started, no further heading should be done, but careful thinning by removal of undesirable growth should be continued.
Upright varieties, such as the Languedoc (see [figure 9]) and Texas, may require heading for a longer time than the more spreading varieties. It is necessary to force them to branch nearer the ground and they should be made to spread as much as possible. Pruning to outside buds and summer pinching will aid materially and make it unnecessary to head back after the first two or three years. Where this is not done, heading may be necessary at the end of the third and possibly to the fourth year if the tree is in rich, deep, moist soil. Another advantage of summer pinching and removal of water sprouts is that the trees are not allowed to develop a thick “crow’s nest” at the end of the stubs where heading back was done the previous winter, making the following winter pruning much easier. The habit of growth of each of the principal commercial varieties is shown in [figures 8 to 12], inclusive.
After the main framework is properly started, further pruning will be limited to thinning out the tree to keep it sufficiently open and to remove all dead, injured and interfering branches. Most of the growth after this will continue from the ends of the remaining branches and as the trees grow higher they will tend to branch more. All cross branches and those that are liable to interfere later should be taken out. All water sprouts should be removed unless they are needed to fill in undesirable open spaces.
As the trees come into full bearing and approach maturity, the vigorous wood growth will cease and will be replaced by a moderate yearly growth of wood which will gradually increase the size of the tree without making it unmanageable. Where trees continue to make excessive wood growth when they should be bearing, the trouble may generally be traced to unusually rich, moist soil, a condition which pruning cannot correct. It may be beneficial to stop pruning altogether for a few years, which will be likely to throw the trees into heavy bearing and thus stop excessive wood growth. After the bearing habit is once thoroughly established, moderate pruning may be done to get the tree back into proper shape.
Fig. 13.—Eighteen-year-old almond trees deheaded six feet from ground, in the Armstrong orchard near Davis. Stubs painted with white lead. Photo taken February, 1914. Compare with [Figs. 14 to 19].
Fig. 14.—Same trees as [Fig. 13], showing growth one year after deheading. Photo taken March, 1915. On some of the trees long stubs were left near the bottom of the trees from which new growth never started. Only a moderate thinning out of the new growth was done.
The mature tree should have its branches so spaced that sunlight may penetrate to all portions of the tree. This is necessary for the continued health and life of the fruit spurs in the lower portions of the tree. If the top is too dense, the new growth can only continue in the top and outer portions of the tree where sunlight can penetrate. When an adventitious bud does start in the center of the tree it immediately makes a strong vigorous growth to reach the sunlight far above. Such a growth is called a water sprout. If the trees are kept so pruned that the shadow on the ground during the greater part of the day is mottled with sunlight while the trees are in full leaf, the small growth may be maintained in the center and the bearing surface greatly increased. Where this is done the trees will not tend to grow as high as they otherwise would. Pruning of healthy, mature trees, therefore, will be limited to thinning out and removal of dead and interfering branches and water sprouts. Portions which grow too high may be brought down by removal close to a shorter and lower branch. By giving this treatment only to small portions of the tree during a season, the forcing of water sprouts may be largely avoided.
Fig. 15.—Same trees as [Fig. 14], showing two seasons’ growth after deheading. Photo taken February, 1916, just after pruning had been completed.
Old trees, or those which, through improper care or neglect have become weak and unfruitful, may often be rejuvenated. One method is to dehead them to a height of about six feet from the ground and to grow entirely new tops. By this method about three years are required to bring the trees back to the point where they are again ready to bear profitable crops. The objections to this are that it is an expensive operation, no crops whatever can be obtained for two years, organisms of decay may gain entrance to the wood, and sometimes the sudden shock to the tree renders it more subject to physiological disturbances. The advantages are that if proper care is given the trees during the rebuilding period, much better formed trees may be obtained and a finer quality of bearing wood be secured throughout the new trees.
Fig. 16.—Same trees as [Fig. 14], showing three seasons’ growth after deheading. Photo taken January, 1917. No pruning done this winter. Trees have not borne more than a few almonds but have a good set of fruit buds.
To be successful, the deheading process must be followed by careful thinning of the sprouts that will be forced from the old stubs. If too much thinning is done the first year, there is danger of those that are left becoming top-heavy and breaking off. This is especially troublesome in sections subject to strong winds. The new sprouts should be left sufficiently thick to help support each other, and yet should be thinned out sufficiently to prevent crowding. At the end of the first season’s growth, further trimming should be done, giving those branches best adapted for the frame of the new tree a chance to take the lead the following season. A sufficient amount of secondary growth should be left to help take care of the excessive sap flow in the shortened tree, but this must be watched to see that it does not interfere with the growth which is to be permanent. By the end of the second year, the permanent branches should be sufficiently strong and firm to permit the entire removal of all other branches. The amount of wood to be left until the end of the second season and then removed is clearly shown in [figures 18 and 19]. The third year the tree should make sufficient growth to restore very largely the equilibrium between the top and the roots and also produce a small crop. [Figures 13 to 17], inclusive, illustrate the steps in rejuvenating an orchard by the deheading process from the start until the trees are again in commercial bearing.
Fig. 17.—Same trees as [Fig. 14], showing four seasons’ growth after deheading. Photo taken December, 1917, after trees have borne their first good crop of nuts. No pruning has been done since January, 1916.
Some growers find it more desirable to cut back only one-half of each tree at a time. The shock to the tree is not so great and the liability to sour-sap correspondingly less. The halves of the tree left standing act as a wind-break to prevent the blowing out of the new growth, which at the same time is less likely to break off because of its slower and more sturdy growth. The objection to this method is that the other half must be cut off the following winter and the shaping process is more or less uneven, and necessarily continued over a long time.
Fig. 18.—Two seasons’ growth before pruning of almond trees deheaded six feet from the ground January, 1914, in the Armstrong orchard near Davis. The tree was only moderately thinned at the end of the first year. Photo taken February 2, 1916.
The other method of rejuvenation is to thin out gradually the dead and weakened branches in the old trees and rebuild them gradually, removing only a small portion in any one year. As the new growth is forced out it is used to replace the old wood where possible. Such a system requires more cutting of small branches high up in the tree to be successful, for it must not be opened to sunlight too suddenly or sunburn will result. The cutting of a large number of small branches tends to force the growth of new buds over a large proportion of the tree and if done moderately many of these will quickly develop into fruiting wood. Eventually, many large branches may have to be removed as newer branches are developed, but this must necessarily be a comparatively gradual process. The advantages of this method are that there is no sudden shock to the tree, there is always sufficient leaf surface to care for any extra supply of sap which may be forced into the tree by unfavorable weather and moisture conditions, and cropping will be continuous.
Fig. 19.—Same tree as [Fig. 18] after pruning. The actual time required to prune this tree was twenty-five minutes. Photo taken February, 1916.
Whatever method of rejuvenation is used, the grower must be very careful from the first to protect all large wounds by some paint or other protective covering, such as asphaltum, to prevent checking and weathering and to keep decay from getting started and working into the heart of the tree. With very large wounds a protective covering must be kept on during the remainder of the life of the tree, or until the wounds heal over completely.