Organic Methods: Growing Feathered Apple Trees in a Nursery
Chris McGuire, Belmont, WI
In high-density orchards of dwarf apple trees, growers generally prefer to plant “feathered” trees with numerous small branches, because feathered trees bear fruit more quickly and provide a faster return on investment. Large conventional nurseries produce feathered trees using synthethic plant growth regulators such as Maxcel, Promalin, and Tiberon.
National organic standards require organic growers to use organically grown planting stock when available. In practice, organic planting stock of apples and other fruits is hard to find and most growers plant conventionally grown stock or raise their own organic trees in on-farm nurseries.
How can organic apple growers raise feathered trees in their on-farm nurseries? With help from a USDA-SARE Farmer Rancher grant in 2018, we compared two organic methods of raising feathered trees. One method is manual leaf removal: repeatedly tearing off the youngest developing leaves from the growing point of the tree. Young leaves produce auxin, the plant hormone which suppresses axillary buds from developing into branches, and by removing young leaves we can release axillary buds along the leader and allow them to develop into branches. The second method is to spray an organic seaweed extract high in cytokinins. Cytokinins generally counteract the effects of auxins and allow axillary buds to develop.
In our experiment, we bench-grafted 60 trees each of nine varieties (Pristine, Williams Pride, CrimsonCrisp, Ashmead’s Kernal, Golden Russet, Egremont Russet, Macoun, Grimes Golden, and Hudson’s Golden Gem) onto G.41 rootstock in March. In April, we planted the grafts in an unheated 34′ x 102′ high tunnel. Prior to planting we applied 2 inches of finished compost over the soil surface in the entire tunnel and afterwards we applied 4 inches of hardwood bark to the entire tunnel as a mulch for weed control. Spacing between trees was 10.75″ within row, 3′ or 8.5′ between rows. As trees grew, we thinned down to a single shoot per scion and we manually removed all branches below 22” above the graft union. We irrigated trees as needed with drip tape throughout the season. We ventilated the tunnel by raising rollup sides and opening end wall doors constantly except during severe storms and cool spring weather.
Each tree received one of three treatments: (1) untreated control; (2) manual leaf removal – tear off 3 young developing leaves near growing tip three times, two weeks apart, starting when leader reached 22” above graft union; (3) spray Sea Crop 16 three times, two weeks apart, starting when leader reached 22” above graft union, at maximum label rate (2 cups/gallon water) to 8-10” at the top of tree. (Sea Crop 16 is an OMRI-listed plant growth regulator made from seaweed. It has the highest cytokinin concentration of any organically approved plant growth regulator we are aware of. However our Sea Crop 16 sprays contained only 50 ppm cytokinin, which is 10-20% of the concentration typically used when Maxcel is sprayed to promote branching in conventional nurseries).
Major pest problems were potato leafhoppers and spider mites. Both were controlled well by sprays (Pyganic for potato leafhopper, oil for spider mites). Other pests were Japanese Beetle and various caterpillars. We saw no disease symptoms.
Grafting success was mixed. Only 3% of Egremont Russet were alive at the end of the year, presumably due to poor quality of purchased scionwood for this variety. Other varieties ranged from 60%-98%. On several grafts, scions began growth in spring but then flagged and died during extremely hot weather in June. This was particularly true in the center of the tunnel (the hottest area).
At the end of the season we collected data on tree growth and branching. Statistical analysis showed these trends (we define a feather here as a branch greater than 4″ in length):
Taller trees had more feathers. Each increase in tree height by 6” resulted in one more feather.
Varieties differed in branching. Macoun had the fewest feathers; then Hudson’s Golden Gem, Pristine, Grimes Golden, Williams Pride, Ashmead’s Kernal, Golden Russet, and CrimsonCrisp. Hudson’s Golden Gem and Macoun averaged less than 1 feather per tree; the most feathered varieties had almost 5 per tree.
Treatment had a significant but modest effect on branching. Leaf removal promoted branching, and the Sea Crop 16 spray actually reduced branching. Leaf removal increased the number of feathers per tree by 0.9, and spraying decreased the number by 0.7. So the magnitude of the effect was relatively small. I am not sure why the seaweed spray decreased branching. It is a complex, naturally-derived substance which may contain chemicals other than cytokinins which actually suppress branching or cause phytoxocity.
Treatment did not affect average feather length. Taller trees had longer feathers. Ashmead’s Kernal and Pristine had significantly shorter feathers than other varieties.
Treatment did not affect the height of the lowest feather.
There was wide variation in tree growth above the graft union, from 2.5’ to 8’. In general, grafts grew much more than is typical in outdoor nurseries in our experience, and many trees were ready for planting in the orchard after a single season of growth. Treatment did not affect the height of trees. Pristine trees were tallest (about 6.5’ above the graft on average), followed by Macoun, Williams Pride, Golden Russet, CrimsonCrisp, Hudsons Golden Gem, Grimes Golden, and Ashmead’s Kernal (about 4.5’ on average)
Published reports state that 10-15 feathers >4” in length are desirable for the tall spindle training system. Only 18 of 379 live trees in our study achieved this! However, many leading commercial nurseries do not produce trees that meet these standards: e.g., Schlabach ‘s and Adams County Nursery consider a tree with 4 branches at least 8” in length to be feathered. 23% of our trees met that standard; ranging from 40% of trees in varieties that branch readily (Williams Pride, Golden Russet, CrimsonCrisp) down to <5% for Macoun and Hudson’s Golden Gem.
We tracked all expenses, including labor time, associated with our nursery. Assuming a labor cost of $20/hour, it cost about $12 per tree produced to graft, grow for one year, and dig up the trees in our nursery, excluding overhead costs of running our farm and excluding the cost of the high tunnel where we grew the trees. Raising trees ourselves may not be costeffective!
The different treatments (leaf removal and seaweed sprays) were quick to apply and only added pennies to this cost. Good grafting success will reduce this cost substantially, since some of the costs incurred (costs of rootstocks, grafting and planting the trees) are incurred regardless of whether the graft succeeds. We calculated that if all grafts were successful, this would have reduced the cost per tree produced to under $9 per tree.
Almost none of the nursery trees set terminal buds on the leader (we have observed this in young trees grown outdoors as well, but it was particularly common in the high tunnel). Vegetative growth continued until early-mid October. We noted that some nursery trees formed many short axillary branches along the leader which did not elongate significantly and were not counted as branches in this study.
In conclusion, we’d recommend the manual leaf removal technique to growers who’d like to grow feathered trees. The effect of this technique was small but noticeable. It might be possible to increase branching further by removing leaves more often during the season. When practicing leaf removal, be careful not to accidentally break off the growing tip itself by trying to remove very tiny leaves. If you do, the tree will produce a dense cluster of vigorous, competing, upright branches – just as if you had made a heading cut. To prevent this, we learned to only remove leaves which are large enough to be clearly distinguishable.
This article was developed with support from the Sustainable Agriculture Research and Education (SARE) Program, which is funded by the U.S. Department of Agriculture – National Institute of Food and Agriculture (USDA-NIFA). Any opinions, findings, conclusions, or recommendations expressed within do not necessarily reflect the view of the SARE program or the U.S. Department of Agriculture. USDA is an equal opportunity provider and employer.
About the Author
Chris McGuire has grown organic produce with his wife Juli at Two Onion Farm in Belmont WI since 2004. They currently raise over an acre of scab-resistant apple varieties on dwarf rootstocks. They sell their apples through a community-supported agriculture program and to grocery stores in Madison WI, Dubuque IA, and Platteville WI.