What we have learned about high-density cherry tree growing

What we have learned about high-density cherry tree growing

Edited, adapted and commented on by Carlos J. Tapia T. Avium Technical Director and Director of content for SmartCherry. 2019

In the past few years there has been a series of advancements in cherry tree growing, including the introduction of rootstocks of less vigor, new varieties, high density conduction systems and covering for controlling cracking because of rain, etc. which are helping to solve the main problems that affect cherry producers in the Eastern United States and the rest of the world.

Considering that producing cherries using dwarfed rootstocks and high-density orchards is still a challenge, in the last 10 years many management techniques for overcoming this challenge have been developed.

Planting high-density fruit orchards are strongly related to the density of tree plantations. Low outputs in traditional cherry orchards can improve substantially with high-density orchards; however, producers have little experience in high-density cherry orchards.

 “A concrete example today is the comparison between a 4 x 2 m. “traditional” system with a density of 1,250 plants/ha., with a 4 x 1.5 m. high-density system; 1,667 plants/ha. Although there is a difference of little more than 400 plants between the two, this number does a great job in precocity, increased potential and sustained maintenance of this potential over time. The big difference in general is in the investment for the greater number of plants for about USD$ 3,000/ha. extra, an investment that plays in favor of the favorable critical points that we described earlier,” commented Carlos Tapia.

In this study, 5 high-density production systems in standard and dwarf cherry rootstocks were compared over the last 8 years. Among the six systems that were tested, the highest cumulative yield/ha. in 8 years was with the vertical axis system (69 tons/ha.), followed by Slender Axe and the “V” systems (59 tons/ha.), the Spanish Bush system (47 tons/ha.), and the traditional central axis system (32 tons/ha.).

Differences in yield between systems were in great measure a function of tree density. There was a linear relation of density and yield of tree plantations (Fig. 1). The vertical axis system had a higher than expected cumulative yield in tree density. The large differences in yield resulted in a difference of three times the cumulative crop value between the Vertical Axis system and the traditional central axis low-density system. With the current rootstocks, we must plant new cherry orchards in densities of at least 700 trees/ha., and with new advancements we envision orchards of up to 2,000 trees/ha.

Dwarf rootstocks

‘Gi.5’ trees are significantly smaller (21%) than ‘Gi.6’, which in turn are smaller by about 9% than ‘MXM.2’ trees. Furthermore, Gisela trees have a «calmer» appearance, which makes them more adequate for high-density plantations. We estimate that Gisela 5 trees must be planted in densities of 1,000-2,000 trees/ha..

Rootstocks had a great influence on the crop in the first 8 years of investigation. With the Hedelfinger variety, ‘Gi.5’ had a higher cumulative yield (57 Kg/tree) while ‘Gi.6’ was intermediate (49 kg/tree) and ‘MXM.2’ had the lowest yield (13 Kg/tree).

«Gisela 5» trees had 10 times the yield as vigorous «MxM.2» trees in the fourth year and 4 times the cumulative yield after 8 years. «Gisela 6» trees had approximately 7 times the yield of «MxM.2» trees in the fourth year and 3.5 times the cumulative yield after 8 years. However, in ‘Gi.5’ they were excessive since the size of the fruit reduced in comparison to Gi.6.

With «Hedelfinger», «Gi.6» trees had a larger fruit size and higher fruit soluble solids than standard size «MxM.2» trees. In contrast, «Gi.5» trees had larger size fruit and lower soluble solids than with the «Gi.6» trees. With fruit varieties like «Sweetheart» and «Lapins», the Gi.5 trees had excessive loads that required that this be managed through pruning or thinning in order to achieve better size fruit.

Modified pruning strategies will be required, such as pruning to lower branches and/or topping of annual material in order to reach a marketable fruit size with Gi.5 and highly fruiting varieties.

New varieties

The yield of cherry varieties in Eastern North America can vary greatly depending upon the soil and climate differences. Our suggestions of new cherry varieties are those that have worked well in our investigation orchards.

Early varieties

Cavalier™ (Rynbrandt cv.) – This early-ripening cherry has a dark red fruit that is medium size, firm and high quality. It should be planted in Gisela rootstocks since they have low productivity in vigorous rootstocks. Bacteria canker tolerance and winter hardiness are good, as well as the resistance to cracking. Self-infertile, in the Polen IV (S2S3) Group, with an early blooming season; multiple pollinators are recommended.

Chelan® This early ripening cherry has a moderate quality, dark mahogany red, firm fruit, of great to moderate size. The fruit must be allowed to ripen completely in order to get the best flavor. Productivity is very good, resistance to cracking is good and trees are more resistant to powdery mildew. Self-infertile, in the Pollen XVI (S3S9) Group, with an early blooming season.

Kristin – This cherry with ripening at the beginning or mid-season has a moderate size, firm, dark red and flavorful fruit. Its resistance to winter is excellent, and the fruit has a moderate to good resistance to rain-induced fruit cracking. Self-infertile, it is in the Pollen III (S3S4) Group, with an early to medium blooming season. 

Mid-season varieties

Benton® (Columbia) – This mid-season ripening cherry has dark mahogany red fruit, firm, of a great size with a good flavor. Yield has been consistently high in trials in New York. The resistance to cracking is very good. It is self-fertile, with a medium to late blooming season.

WhiteGold® – This mid-season ripening blush cherry has a clear yellow-colored flesh with a firm yellowish-red skin blush, moderate to large in size, good flavor. The trees are very productive, resistant to cold and well adapted to the growth conditions of Eastern North America, with a low susceptibility to cherry leaf spot and bacterial canker. The fruit is moderately tolerant to rain. Self-fertile, with a mid to late blooming season.

Glacier® – This mid-season ripening cherry has large fruits that are dark mahogany red in color with very good flavor, but less firmness than other fresh market varieties. «Glacier» could be an excellent fruit for local markets with fresh products. It should be grown on early rootstocks that control the size. Moderately susceptible to rain. Self-fertile, with a mid to late blooming season.

Lapins – This mid-season ripening cherry has large fruit that is dark mahogany red in color with good flavor and excellent firmness. Lapins produces exceptional fruit for immediate sales locations. It has had surface pitting problems when it is shipped from the west coast. In New York it also suffered lesions in the 2003 and 2004 winter. However, it is a productive variety, self-fertile and exceptional and is very rain tolerant.

Late varieties 

Regina. This late-ripening cherry is a new variety that is more promising for the East. The fruit is large, dark red in color, very firm with a long stem. It’s very tolerant to the rain. It is a late bloomer, which helps it to avoid frost, but it requires a variety of pollinators that also bloom late. Hudson has worked very well in our trials in Geneva. It is a timid cultivar unless grown in one of the Gisela populations. It is a late bloomer.

Sweetheart – This very late-season ripening cherry is the best for the end of the season. The fruit is very high quality, a brilliant red color, firm and has a good flavor, but the size is moderate. A tree that is easy to grow, with an extended shape and early, heavy crops on all rootstocks. It has a good winter resistance and bacterial susceptibility to canker and the fruit is moderately resistant to cracking. The tree is self-fertile, with a mid-season bloom. In Gisela rootstocks, it is often too productive and requires load management of the crop to achieve an acceptable size. 

Keeping the trees alive

The saying is that «cherry trees love to die». With heavier soils many times survival of cherry trees is poor. There are 4 major management approaches that are used to limit tree mortality.

Using planting strips (“camellones”, in Spanish): Cherry tree death is many times associated to winter damage and excessive soil humidity. In some cases, death is caused by root rot of the Phytophthora and other cases it is due to a winter lesion and later infection of the bacterial canker.

It is evident that the use of planting strips improves the experience in this type of soil, but it is assumed that this type of “tool” will be used for the rest of the orchard’s life in terms of pruning and harvesting operations.

This probably is due to better oxygen levels in the soil and the decrease in water accumulation in the autumn and spring. An important note is the planted trees in planting strips can dry rapidly due to the summer heat in comparison to the flat ground.

Intensive soil use: Often, winter damage in cherry trees is associated with wet areas in the field. The use of an intensive cultivar on each lane has had the result of much less winter damage to cherries. Many kinds of “grass” may be used such as lawn or legumes to get rid of excess wetness in autumn and spring.

Use of resistant rootstock: None of the cherry rootstocks currently available is resistant to Phytophthora root rot; however, the Gisela rootstocks show a larger tolerance than Mahaleb, MaxMa, but maybe no more than Colt.

Bacterial canker control: In wet climates throughout different parts of the world in areas where cherries are grown, it is important to plant varieties that are less susceptible to bacterial canker. Furthermore, there are 3 management practices that are important to avoid tree death due to this disease. (a) Pruning must be delayed until growth begins in the spring or pruning in the post-harvest period. However, this latter practice limits having season history to do a pruning task in function of the characteristics of cold accumulation, bud quality, etc. (b) using a copper spray program that includes 2-3 sprayings in the period of leaf fall (20% of leaf fall and 90% of leaf fall) and 2-5 sprayings in the winter until the swollen bud stage. (c) never cut flush with the shaft. Always leave a “block” of 10-12 cm. If the canker gets in this piece, it will slowly reach the trunk, but it will not infect it directly. 

 Young tree formation

Traditionally, cherries receive little training and pruning during the first five years.

However, in high-density orchards, investments in the adequate tree formation pay dividends. Furthermore, beginning with the correct tree will result in larger early production. This has been widely proven over time.

Plant a high-quality tree. The optimum tree for planting is different according to the system. For vertical axis systems, a high caliber tree and with anticipated presence is the best and needs little pruning and training during the first two years. 

The larger caliber early-bearing tree used in the Vertical Axis and Slender Spindle has much higher production in the third and fifth year than the small caliber tree. For the bush systems and “V” for example, a medium caliber tree is better since these systems employ an important leader dominance in the planting.

 “In the Chilean reality, there are still now successful experiences with plantation-finished trees with anticipated presence. It is thought that, having anticipation, the homogeneity of the plants is limited. However, a number larger than 5 of these anticipations could generate a “plus” in the precocity of the high-density plantation. Anyway, when this idea is brought up, is that these anticipated branches be of a homogenous vigor and always thinking about the use of medium to low vigor rootstocks,” Carlos Tapia pointed out.

Minimizing axis cuts during the first few years. The pruning cuts repeated in the first 3 years reduced the yield, while minimal pruning the first 3 years gives a result of early high yield. This means that the one-year branches should not be intervened in thinning.

To develop lateral branches without topping to successfully incorporate minimum pruning of young cherry trees, specialized branching techniques to overcome strong apical dominance.

This technique allows minimum pruning but proper placement of extremities all along the leader. Bend flat branches. Cherry trees are very apically dominant, which results in vertical angles of the branches.

Cherry orchard management in adult stage.

High-density adult cherry trees in dwarfing rootstocks have two main problems: dense canopies with little light on the lower covering and possible excessive loads with small fruit.

What is recommended to overcome these problems:

Aggressive pruning. We recommend that mature trees above all in series like Gisela be pruned more aggressively than trees in more vigorous rootstocks. Pruning must include the elimination of most of the thin, shaded wood each year. Besides the continuous renewal of thick material that has lost its productive capacity in young wood.

Keeping light exposure on the lower part of the tree. In high-density plantations it is easy to allow the development of very thick crowns. Cherries need good light distribution on the lower part of the tree to produce good quality fruit and healthy shoots for harvest in the following season.

The best light exposure on the bottom is better achieved with renewal pruning of the extremities. The elimination of 1-2 large branches in the upper or middle part of the tree each year, prior to blooming or after the harvest, depending upon this objective, renewal or elimination respectively.

Conclusions

Considering yield, the size of the fruit, soluble solids and gross economic returns, the central axis systems, be it more traditional or modified, these were the best systems from this trial, this was not so with the more bush-trained formation systems.

High-density orchards with a group of management strategies that we call «Integrated system of cherry production” may result in a constant high-quality cherry production. Essential points of integrated systems are: high-density trees (> 300), dwarfed or semi-dwarfed rootstocks, new varieties, planting strips and inter-row planting when necessary and “minimum pruning” during the first 4 years, besides renewal pruning to improve light, distribution inside the crown, aggressive pruning to increase the fruit size, irrigation, GA3 applications in order to improve the fruit firmness and other crop and nutritional management in order to sustain this system over time.

Figure 1. Relation between tree plantation density and accumulated yield of 3 cherry varieties (Hedelfinger, Lapins, Sweetheart) in MXM.2, Gisela 5 and Gisela 6 rootstocks no matter the conduction system.

Figure 2. Relation between tree plantation density and cultivar value in cumulative profitability of 3 cherry varieties (Hedelfinger, Lapins, Sweetheart) in MXM.2, Gisela 5 and Gisela 6 rootstocks no matter the conduction system.

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