Tree Fruit Leader, Vol. 5(1) April 1996

High Density Cherry Systems

By Helmut Arndt, Horticultural Specialist BCMAFF, Kelowna

Sweet cherry trees in the Okanagan Valley have traditionally been planted at wide spacings (20' by 20') and have been encouraged to grow vigorously to fill the allocated space. Trees are typically trained to an open centre system. Growth with this system is upright being influenced by both variety and the vigorous rootstocks Mazzard, Colt and Mahaleb. Most varieties do not branch easily and thus require excessive heading of both main, uprights and laterals. The consequences of this severe and continual heading are delayed fruit production and excessive amounts of growth. The fruiting zone in open centre trees moves continually upwards as trees get older making harvesting and pruning more labour intensive. It has been shown in most economic analyses that labour costs account for 75% of variable costs when producing cherries. Overseas research shows that a 10 foot ladder requires 30 to 40% of a pickers time just to move and climb the ladder.

So What are the Alternatives to the Open Centre Tree?

Over the years growers and researchers have tried many different training systems on sweet cherries. Some showed more promise than others but there isn't one system that has dominated and been recommended as the accepted training system for sweet cherries. However, the following systems have been tried in different countries and found to work for some growers.

Central Leader /Modified Central Leader

The first system I would like to look at is the central leader or modified central leader. This system starts with a feathered or whip tree and is allowed to grow similar to a central leader apple tree. Limbs are allowed to form either as whorls or at intervals around the trunk to a certain predetermined height and then topped to a weak side limb. Strong limbs are removed as the tree gets too dense but new main laterals can be developed because we still have the central trunk. This system is more manageable than the open centered tree because vigor is being controlled from the trunk and the flat angled limbs that have been developed during the formative years. This means that as the laterals on the young tree start to develop tooth picks and/or clothes pins should be used to flatten the branch angle. It is most important with a variety like Lapins which has a great tendency to want to grow upward. Sweetheart on the other hand is much more grower friendly and doesn't require the degree of training. This system when using the mazzard rootstock can be planted at distances of 6 by 6 metres, 4.6 by 6 metres, 4.6 by 4.6 metres, or 2.4 by 4.8 metres, 2.3 by 4.6 metres or a combination of this sort with the eventual removal of every second tree when things get too dense and fruit production and quality fall off. This system is manageable but still requires ladders and a large labour force.

Vogel/Spindle System 

This system of tree training was developed by Mr. Tobias Vogel, extension agent in the Bavaria region of Germany. 

Trees are planted as whips and headed at 80 cm. Laterals are allowed to develop and angles are set to the horizontal by using tooth picks and clothes pins. Normally 4 to 5 laterals are allowed for the first whorl. No more heading is done on the central leader for the next 3 or 4 years unless there is poor growth. This lack of heading allows the central leader to grow 3 to 4 feet with the eventual development of a whorl of 4 to 5 laterals at the end of each growing season. The laterals are all spread to the horizontal and left unheaded. Strong angled laterals are removed. The empty areas along the central leader which appear bare at the outset normally fill in with branches in two or three years depending on variety. Lateral branches are not cut back until they start to bear fruit. This means only older wood is cut into which produces less regrowth than one or two year old wood. Laterals may be pinched during the growing season to induce some side shoots and possibly to reduce vigor. 

Trees on this system are spaced 3 by 5 metres and are allowed to reach a height of 4 to 5 metres. 

The top of the tree is managed by cutting to a weak lateral. Mature trees require constant renewal of branches and this is accomplished by stub cutting and allowing shoots to develop on these stubs which are then selectively thinned out to form new fruiting wood. The advantage of this system is that the lack of pruning in the early years gets the trees into earlier production and keeps vigor to a minimum.

Close Spaced Spindle/Axe Plantings

This system is similar to the Vogel system, however, the trees are planted at a much closer distance. It is a system that has been introduced in Germany by Dr. Fritz Zahn from Hamburg, Germany. The spacing used in this system is 1.2 by 3.6 metres, 1.5 by 4.2 metres, 1.8 by 4.2 metres, etc. 

Trees are left unheaded at planting and all strong laterals are stub cut or removed. The leader is left unheaded for the first 3 to 4 years until fruiting occurs. 

This central leader type tree has only weak laterals which are constantly renewed so that they are no older than 4 to 5 years at any time. It is expected that weak laterals, in time, will fill the spaces between the whorls. 

Summer pruning is a must in this type of planting to keep the vigor under control. Summer pruning can be done at any time during the growing season. To bring more shoots into fruiting summer pruning should be done 5 to 6 weeks after full bloom. One year old shoots are cut back to 6 and 8 inch stubs. This could include one year old upright shoots as well. If you want to get reduced regrowth then summer prune after harvest or into early September. 

Remember that you don't want laterals to be more than 50% the size of the main leader at anyone time. 

Stub cutting and summer pruning are the keys to this system. Height of this system is 3 to 4 metres.

Angle/Marchand System 

In this system trees are planted 2.5 to 3 metres apart in the row by 4.2 to 4.8 metres between the rows. Whips are planted on a 45 degree angle or straight and then pulled to a 45 degree angle. Shoots or uprights that develop from the angled leader are trained on a post and wire support system at right angles to the leader. To promote more consistent laterals to develop Promalin is painted on the buds at the time of bud swell in late March or early April. The rate of Promalin is 3 parts dark latex paint to 1 part Promalin. Application may have to take place over several days to a week because buds don't all swell at the same time. The upright laterals may be pinched once or twice during the growing season to promote small or weak side shoots to develop. The laterals should be spaced 12 to 16 inches apart on the main trunk and renewed if and when they become too strong and vigorous. This can be accomplished by stub cutting and selecting the appropriate replacement shoot. 

The height of this system is somewhere between 2.4 to 3.0 metres. Particular attention must be paid to the main leader that it doesn't grow upright. Also attention has to be paid to strong upright laterals so they don't become stronger than the main leader. Remember the 50% rule. The main advantage of this system is that most or all of the labour is from the ground. The main disadvantage is that cherry trees want by habit to grow upright. Therefore more than normal attention has to be paid to tree training both during the growing and the dormant seasons. 

Tatura Trellis

This system from Australia is an example of a V-shaped canopy. This is accomplished by means of a trellis that spreads the limbs out over the row middles. The trellis is elaborate and expensive. Spacing is 1.5 by 4.5 metres. The V-trellis is about 2.4 to 3.6 metres in height depending on whether you use long or short poles for the trellis. Five wires are positioned 30 cm. apart on each side of the trellis. The first wire should be 50 to 60 cm. from the ground. 

Whips are planted at 1.5 metres and headed at 20 to 30 cm. Two scaffolds are trained one on each side of the trellis. Treat these scaffolds with Promalin at bud swell to encourage lateral branching. Minimal pruning during the formative first three years and only bending and tying will induce earlier fruiting and reduce vigor. Once the trees have come into the cropping phase excess laterals and growth can be removed. 

The main disadvantage of this system, besides cost of the support system, is that it is difficult to keep the vigor under control without a dwarfing rootstock. The main advantage of the V-trellis is that it allows maximum light interception and light distribution in the tree. However, a lot of work is required in tree training and keeping the V free of upright shoots.

Production on this system has been shown to be the highest of the systems mentioned.

An alternative method to this system is to plant two feathered trees, one for each side of the trellis. Because these trees can be developed with minimal pruning they will generally come into production 1 to 2 years sooner than trees that have been trained to the other method.

Spanish Bush

This system developed in Spain is just what the name implies - a Bush. The goal is to harvest all fruit from the ground therefore a dwarfing rootstock should be used. Mazzard, Colt and Mahaleb could be used but vigor control may be a serious problem.

Whips are planted 1.8 to 2 m by 3.6 to 4 metres. After planting they are headed at 20 to 30 cm. and 5 to 6 laterals are allowed to develop in the first year. As these laterals grow they are tipped or cut back by a third when they get 30 to 40 cm. in length. This is done during the month of June and again in July if enough growth occurs. Strong uprights and crossing branches are removed either in the dormant or summer season. This tipping of laterals is also continued in years 2 and 3. The idea is to end up with a bush which in the third growing season should start to bear fruit. Once fruit bearing has started then serious pruning has to occur especially in the centre of the tree. At this time the centre should be opened up to allow for maximum light penetration. The centre should be kept open with only a few weak shoots remaining in the middle. In Spain trees are topped after harvest to 2.4 metres to maintain tree height.

The Spanish Bush is meant to be easy and economic to manage, but as with all systems, proper irrigation, fertilizers and rootstocks combine to make it a success.

One of the main drawbacks of this system will be the control of vigor especially with a variety like Lapins which has a very upright growth habit. Cherry orchards with our vigorous rootstocks will be difficult to maintain in high density spacing. The lack of a good dwarfing rootstock has greatly limited our attempts with earlier high density plantings. Failure has come in controlling vigor and heavy set has reduced fruit size. Present day European rootstocks look good under their conditions, and some high density plantings have performed well. We have to be extra careful, however, not to get caught up with high density UNTIL we do a great deal of testing under our conditions using our varieties.

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