As labor costs increase, worker productivity in agriculture is becoming an improtant part of the agriculutural puzzle. As in all tree furiuit production, cherries are being planted closer and closer together. Planting at higher densities allows for orchard space to be filled more quickly, which brings earlier yields and quicker investment returns. Although dwarfing rootstocks are relatively new for cherries, growers thoughtout the world are getting into high density cherry plantings. These higher density systems demand an array of pruning and training techniques and other horticultural practices to bring the trees into early bearing and maintain proper size and space. The most popular of the systems is the Spanish Bush of Spain, which provides for smaller trees, with denser plantings. The more manageable trees make labor much easier and the higher densities provide for earlier yields.
Although almost all the plantings in Spain are on non-dwarfing rootstocks, the very poor soils, combinbed with standard Mahleb stocks work well to produce a nice dwarfed tree when trained in Spanish Bush style. Cherries have historically been grown on Mahleb and Mazzard rootstocks which generally produce tall, vigorous trees which yield almost no fruit until their sixth leaf. For those reasons the use of dwarfing, precosious rootstocks, in conjunction with the Spanish Bush system are being considered for plantings here in the Pacific Northwest. The three dwarfing, precosious rootstocks which are recieving the most attention are Giesela 5,6, and 12. Although 6 is reasonably precosious, it has proven to very difficult to maintain in size. Both 5 and 12 are showing good production results and are proving to be fairly size manageable in our regions soils. One note should be made that heavy pruning is necessary to maintain good fruit size on all of the Giesela rootstocks.
A trickle irrigation system is generally implemented in Spain, but that trend has not carried on to the Spanish Bush orchards here in the Northwest. A trickle system is used in Spain in order to avoid using cover crops and to prevent much weed growth around the trees. Because there is so much low level canopy on the trees avoiding herbicide use is very beneficial, so the lack of weeds is very beneficial.
Six to nine feet, by twelve feet is the popular spacing Spain with the system, but to site conditions and equipment sizes here in Northwest a somewhat larger spacing is probably necessary. The quality of our soils will also play a part in spacing as maintaining tree size can be difficult. In order to avoid crowding and facillitate easy farming spacings of eight to ten feet, by fourteen to eighteen feet are recommended.
Well managed Spanish Bush orchards in Spain have proven to produce large, high quality yields in the tree's fourth leaf. Much of this can be attributed to the high densities, but the long growing season also plays a big part in this prodcution standard. That long growing seasons allows orchardist to push the trees early and make the necessary heading cuts. Because Northwest experiences a substantially shorter season it is proving difficult to keep up with the prescribed pruning schedule. To combat this lack of growing season growers here in Northwes are turning toward the use of precosious rootstocks in order to meet the early fruiting goal of the fourth leaf. In order to understand the system well, an outline of the pruning up through the fourth leaf is helpful.
A heading cut is made at twelve to fourteen inches above the soil, just before bud break. The hope is that three to four shoots will develope, and through the use of toothpicks they can be spread to a decent angle. Some growers are even using wires to spread the shoots and promote good sunlight distribution. These first branches should be grown to a lenght of twenty-four inches and then headed back to twelve inches again. It is critical that this cut is not made until the branches are of the right length and have enough vigor to throw more strong shoots. Ideally this heading cut will produce another three to four shoots and then they should be grown out to twenty-four inches. Once those branches reach the proper length and vigor they should be headed back to between twelve and sixteen inches. In Spain the growing season is long enough that all three of these heading cuts can be made in the first season, but with our shorter season growers are finding it difficult. It should be noted that it is absolutely essential to wait for the correct length and vigor when making these first heading cuts. If that means waiting until the second leaf to make the third heading cut, it is highly recommended that you do so.
Early dormant pruning should be done to eliminate any crossing and excessively growthy branches. At this time every effort possible should be made to begin slowing the tree down and begin getting it ready to begin set fruit by the fourth leaf. Fertilizer should be cut back to a bear minimum and thinning cuts to open up the center of the tree should be made. There is also some work being done with using Promaline at this time to encourage branching without having to make any cuts and maintain good vigor.
Ideally the trees will be entering their flowering and fruiting state by the third leaf. All pruning done at this time should be made to maximize fruit quantity and quality. Following harvest the vertical limbs should be headed in half and three or four of the strongest laterals should be cut back in an effort begin wood renwal. Wood renewal is critical in this system as it is necessary to produce the highest quality fruit. A cycle should be established so that no fruiting wood is older than four years. Thinning cuts should also be made to maintain good light penetration and distribution.
By this time the trees should have entered their mature fruiting cycle, so a system of pruning three times through the season can be established. Pruning should occur post bloom, post harvest, and then again in late August to early September. The first pruning at post bloom should be done to balance the crop load and help with any sizing problems. The post harvest pruning should be done continue wood renewal and maintain good light in the canopy. The final pruning of the season is strictly for size control. Mechanical topping should be done to keep the trees at an eight foot maximum height and they should be hedged in order to prevent any cross row shadowing.
If growers here in the Northwest can successfully modify this Spanish Bush system to our environment, I feel that many benefits will come about. An increase in early production, and greater efficency of labor are definetley two things that our Northwest cherry growers benefit from.
1. Hansen, Melissa. Larger cherrries can be achieved by heavy pruning,GoodFruit Grower Feb.15, 1997, (10-11)
2. Kappel, Frank. Cherry rootstocks and summer pruning, GoodFruit Grower May 15, 1995, (27-29)
3. Long, Lynn E. Spanish Bush increases worker productivity, GoodFruit Grower, Feb. 1, 1997, (27-33)
4. Long, Lynn E. European cherry growers try high density systems GoodFruit Grower Feb. 1, 1995, (24-25)