Top-working
Top-working is a method of changing part or all of a fruit tree over to a different variety (or varieties). This a common practice in commercial fruit production where a variety may fall out of favor and different variety becomes more profitable. Top-working can also be used in a home orchard where the family wants to change a variety or add varieties.
Large Scaffold Branches or Entire Trunk
Sometimes you may be top-working a tree that is 15 or more years old with large scaffold limbs that are several inches in diameter. This type of top-working usually involves bark grafting or wedge grafting in April with dormant scion wood.
Top-working is a method of changing part or all of a fruit tree over to a different variety (or varieties). This a common practice in commercial fruit production where a variety may fall out of favor and different variety becomes more profitable. Top-working can also be used in a home orchard where the family wants to change a variety or add varieties.
Large Scaffold Branches or Entire Trunk
Sometimes you may be top-working a tree that is 15 or more years old with large scaffold limbs that are several inches in diameter. This type of top-working usually involves bark grafting or wedge grafting in April with dormant scion wood.
To the right is clip of the image for the Whitney's Grafting home page showing an apple orchard that has just been top worked. The top of each stump is yellow from the Doc Farwell's Seal and Heal used to protect the cut surface after the bark grafting is complete. Note the size of the orchard (immense) and the size of the trunks of the trees top-worked (6"+ across).
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Smaller Diameter One- to Three-Year Old Wood
On younger, smaller growth (one to three year old wood) cleft grafts and side grafts may be used in April with dormant scion wood. The whip and tongue graft can be used on well positioned one-year growth for April grafting as well.
Summer Chip Budding On Current-Year Wood
What follows is an explanation of how to create new, young limbs (current-year wood) on a mature tree that may be 5 to 15 years old, so that summer budding (both chip and T) techniques appropriate for current-year wood can be used.
[ Note: These same techniques of dormant season pruning can also be used to position one-year, two-year, and three-year wood on older, larger fruit trees for April cleft grafts and side grafts with dormant scion wood. The basic process with older trees is to generate new growth closer to the truck by cutting scaffold limbs back to smaller side limbs (to avoid a stub). ]
In the first example below a two-inch scaffold branch on an 8 year old tree had a heading cut (pruning cut made in April 2019 is visible in lower left hand corner of photo) to stimulate new shoot development near the cut. Dormant season pruning cuts typically create new growth (while summer cuts inhibit new growth). Thus, this dormant season cut, produced several new shoots (2019 wood) that were relatively vertical (often referred to as "suckers" because generally these vertical shoots would be undesirable). Usually we would remove these shoots or cut them back to just a couple of buds and have them fruit. This would be done in mid-June to mid-July. However, when we are top-working a fruit tree we can leave some of them to chip bud in the summer (in August) or cleft graft or side graft them the following April using dormant scions. In the example below you can see that chip buds have been placed on all 5 suckers and the end limb which goes of to right hand side of the picture. All 6 if these limbs are 2019 growth (current-year shoots). Technically this end limb off to the lower right side of the photo is not a sucker, but a terminal shoot on the large 2 inch scaffold that had the heading cut. In April of the next year the 6 limbs with the chip buds will be cut off above the chip buds to induce the chip buds to form new side branches that will be tied at a 45 degree angle as they grow out to form the fruiting limbs for this scaffold limb. Tying limbs off at 45 degrees induces the formation of fruit bud and side branches, while an upward growing limb suppresses fruit bud and side branch formation.
Down below is a photo of an example of heading back the central trunk on an 8- year old fruit tree to stimulate the development of new side shoots that can be used to chip bud or graft new varieties. The heading cut on this 4-inch trunk was made in April 2019. The heading back occurred where there was a small limb forming over there on the right side right below the cut. Usually a heading cut on larger limbs and trunks will be made just beyond a small limb so that nutrient flow can continue out to a terminal branch. Note that a few side shoots (2019 wood) developed for receiving chip buds in the summer of 2019. Also observe that below these new side shoots are large scaffold limbs that were left as "nurse limbs" to provide nourishment to the tree during the 2019 growing season as it developed the new 2019 growth. The new side limbs (2019 growth) were chip budded in August, 2019. They will be cut back just above the new chip buds in April, 2020. These buds will produce new shoots that will grow 30 and 40 inches in 2020. These new limbs will be directed outward at a 45 degree angle and will form the new scaffold limbs for the tree and those larger lower limbs will be removed in early April, 2021. If any of the chip buds failed to take, then grafts (either side grafts or cleft grafts) can be made on those limbs in April 2020. As the new chip budded limbs develop, those large nurse limbs below will be removed.
Below is a President Plum (E) limb that was placed as a chip bud in August 2019. In 2020 it grew about 10 inches and set fruit buds (plums can set fruit buds on one-year growth). In 2021 that limb bloomed and limb that has several plum on it but only grew about 6 inches because of the fruit load.
Below is an Opal Plum (E) that was side grafted in 2019 and put out about 16 inches of growth that year. In 2020 it put out another 16 inches and set fruit buds, resulting in this crop in 2021. The host tree is an Italian plum that has been converted over to a multi-variety plum with 6 different varieties. Some were chip budded and others were side grafted. I will probably add two or three additional varieties since I am using it as demonstration top-worked tree.