Apr 7, 2007The Tall Spindle System: Apple Orchard Design For The Future
After years of experimentation, Terence Robinson believes he knows what a modern apple tree should look like.
It’s taller than people once thought it would be, 10 feet tall, but the trunk is really small and there are no scaffold branches to speak of. It sits along a three-wire trellis with other trees, spaced about three feet apart, in rows 11 feet apart, on an M.9 or similar dwarfing rootstock. It fruits early, bearing 15 to 20 apples in its second year.
Growers who plant trees like this have to learn a different training and pruning system, but if they plant the right varieties they should make money.
Robinson spoke during the Great Lakes Fruit, Vegetable and Farm Market EXPO in Grand Rapids, Mich., last month. The Cornell University horticulturist explained in detail how to establish such an orchard, how to prune and train it and how much income it should provide.
He and his fellow researchers at Cornell, especially Stephen Hoying, began studying the issue intensely 10 years ago and now speak confidently about what they call “the tall spindle system.”
The system evolved out of a period of experimentation, by both growers and horticultural researchers, that started 50 years ago with the abandonment of seedling rootstocks and the search for trees that were more manageable, bore fruit sooner and yielded more per acre. Tree densities soared from as few as 35 trees per acre on 30- by 40-foot spacing to more than 2,500 in some systems, and heights fell from 50 feet down to pedestrian size – the size of bushes. Investment per acre skyrocketed as trees per acre increased.
Not everything worked. Trees could be too short as well as too tall, too dense as well as too spaced out.
“By the late 1990s, an amalgamation of these trends gave rise to a new system we began calling the tall spindle system,” Robinson said. “It incorporates aspects of the slender spindle system, the vertical axis system and the super spindle system. The planting system achieves the goals of very high early yields, high sustained yields and excellent fruit quality, while moderating the initial investment compared to the super spindle system.”
The important components of this system, as Robinson lists them, are: 1) high planting densities, 2) dwarfing rootstocks, 3) highly feathered nursery trees, 4) minimal pruning at planting, 5) bending feathers and branches below horizontal, 6) no permanent scaffold branches and 7) limb renewal pruning to remove and renew branches as they get too large.
Tree densities can vary from as many as 1,452 trees per acre on a 3- by 10-foot planting to 838 per acre on a 4- by 13-foot planting. The proper density considers the vigor of the variety and rootstock and the strength of the soil, Robinson said. Closer spacing is recommended for weak and moderate vigor varieties such as Honeycrisp, Gala and Red and Golden Delicious, and wider spacing for vigorous (McIntosh, Fuji, Mutsu) or tip-bearing (Rome, Gingergold, Cortland) varieties.
Row spacings should be narrower on level ground and wider on slopes.
Trees should be on dwarfing rootstocks such as M.9 and B.9. Newer rootstocks from the Cornell Geneva series (G.16, G.11, G.41) are fire blight resistant and are working in tall spindle system orchards in New York, Robinson said.
Within rootstocks, however, there are vigor differences. Weaker clones are recommended on virgin soil and with vigorous varieties, while more vigorous rootstocks should be used with weaker scions or on replanted ground, he said.
Robinson’s economic analyses show that early bearing, in the second and third years, is important if high-density orchards are to overcome the high investment costs that come with planting so many trees per acre.
Establishing a tall spindle orchard on a 3- by 11-foot spacing would cost $8,580 an acre just for trees. When anchor poles, inline poles, trellis wire and labor are added, cost per acre rises to $11,080, he said.
To achieve bearing in the second year, high-quality trees must be planted, he said. Whips and small caliper trees will not bear significant quantities of fruit until year four or five.
“We recommend that the caliper of trees used in tall spindle plantings be a minimum of 5/8-inch and that they have 10 to 15 well-positioned feathers with a maximum length of 1 foot and starting at a minimum height of 30 inches on the tree,” he said.
“Generally, nursery trees in North America have not had this number of feathers until the last two years. Many nursery trees have three to five long feathers instead of 10 short feathers. The tree with few long feathers requires more branch management.”
The most important method of inducing cropping and reducing induced juvenility is tying down the scaffold branches below horizontal, he said.
At planting time, all the feathers must be weighted or tied down to induce cropping and prevent them from developing into scaffold branches. If the feathers are not tied down, limbs become too strong and invigorated, making it difficult to contain the tree, he said.
“This simple change in tree management allows for long-term cropping of many feathers and little invasive pruning for the first five to eight years at the very close spacing of the tall spindle system,” he said.
After the initial tying down, new lateral branches that arise along the leader will not need to be tied down. If not pruned, they will bend with cropping, he said.
“The precocity of the rootstock induces heavy cropping and a natural balance is established,” he said.
Crop load management
“Varieties differ in their biennial bearing tendency, and this must be incorporated into crop loads allowed on young trees,” he said. “For annual cropping varieties like Gala, we recommend crop loads of 15 to 20 apples per tree in the second year, 50 to 60 apples per tree in the third year and 100 apples per tree in the fourth year. For slow-growing and biennial bearing varieties like Honeycrisp, crop loads should be half that used with Gala.”
Mature canopy shape
The tall spindle tree is essentially a 10-foot trunk with small fruiting branches along its length, Robinson said. To achieve this in three years, the central leader is not cut (headed) at planting. Given the size of the tree from the nursery, 5 to 6 feet tall, it is already half its mature height at planting time.
This tall, thin tree needs support, or when it is fully leafed out it may break in the wind, he said. A three- or four-wire trellis is needed before the first leaves appear. Because of tree density, individual tree stakes are prohibitively expensive. The tree is tied to the trellis and is not headed until reaching its mature height, about 10 feet in year four or five.
The narrow, slender shape helps ensure most of the canopy is exposed to good light, resulting in excellent fruit quality, he said.
“For the tall spindle system, maintaining a conic shape as the trees age is critical to maintaining good light exposure, fruiting and fruit quality in the bottom of the tree,” Robinson said. “In our experience, the best way to maintain good light distribution within the canopy as the tree ages is to remove whole limbs in the top of the tree as they grow too long.
“We recommend the annual removal of one or two upper branches completely. To assure the development of a replacement branch, the large branch should be removed with an angled or beveled cut so that a small stub of the lower portion of the branch remains. From this stub a flat, weak replacement branch often grows. When this style of pruning is repeated annually, the top of the tree can be composed completely of young fruitful branches, thus maintaining the conic shape of the tree.”
Testing of the tall spindle system began at Geneva in 1997, Robinson said. Since then, it has been the second highest yielding system – behind the super spindle – but the most profitable.
That was achieved while planting less well-feathered trees, which were not available for planting 10 years ago. Newer plantings, with trees planted with more feathers, have achieved higher yields, he said.
“We expect even greater yields from the new trials since we have even better quality trees,” he said.
In orchards planted in 2002 with trees with seven to eight feathers, after four years McIntosh and Honeycrisp are yielding at twice the levels of the traditional vertical axis trees. McIntosh yields in the fourth leaf reached 771 bushels per acre and Honeycrisp reached 578 bushels per acre, he said.
“The key objectives for a new orchard are to maximize yield in the early years and still effectively produce large yields of high-quality fruit after the trees are mature,” Robinson said. “The tall spindle system accomplishes these objectives by combining high tree planting densities, highly feathered trees that have many small branches rather than a few large branches, minimal pruning at planting or during the first three years, branch angle management by tying down all feathers at planting to induce cropping and prevent the development of strong scaffold branches that cause difficulty in tree management in later years, and branch caliper management by the systematic removal of large branches to keep the tree manageable.”