The bud union (also call a “graft union”) is where a nursery grafts a bud onto rootstock. Every fruit tree you buy, whether bareroot or containerized, has a visible bud union. It looks like a crook or jog above a straight rootstock, just below the straight trunk, and you can use it as a ready-made planting depth marker for your young fruit trees!
Above the bud union is the “scion” or actual variety of fruit that you hope to harvest, and below the bud union is the rootstock, the actual roots of the tree. Rootstock also determines the amount of dwarfing characteristics the fruit tree will have.
|Fruit Type||Rootstock Type||Plant Bud Union|
|Apple, Apricot, Nectarine, Peach, Pear, Plum, Prune||Seedling/Standard||1-2″ BELOW ground level|
|Apple||Dwarf or Semi-Dwarf (EMLA, Malling, Geneva, Bud or Budagovsky, 9, 26, 7, 30, 106, 111, etc.)||3-4” ABOVE ground level|
|Pear||Dwarf or Semi-Dwarf (OHxF 97 or 87, PyroDwarf, Pyro, etc.)||3-4” ABOVE ground level|
|Sweet and tart cherry||Seedling/Standard (Mazzard)||1-2″ BELOW ground level|
|Sweet and tart cherry||Semi-Dwarf (Mahaleb)||1-2″ BELOW ground level|
|Sweet and tart cherry||Dwarf (Gisela, etc.)||2-3″ ABOVE ground level
How Rootstock Is Affected
With Seedling or Standard rootstocks, covering the bud union helps to reduce the amount of “suckering” that can occur. When varieties are budded onto a Standard or Seedling rootstock, they will grow as if they were on their own roots and will reach their natural full size. Even if there is “scion rooting” the ultimate size of the tree is not affected.
With Dwarf and Semi-Dwarf rootstocks (including size control or precocious rootstocks) it is important not to plant too deep, especially if you intend to make the most money for them. Some types of rootstock have their own special planting depth requirement, but usually if you plant them too deep you will end up with a fruit tree similar in size to Standard or Seedling.
In the old days, all sweet and tart cherries were budded on either Mazzard (full-size Standard) or Mahaleb (often called Semi-Dwarf) rootstocks. Both are Seedling rootstocks and both can be planted with the bud union one to two inches below the ground level. The choice of which rootstock the nursery used was often determined by compatibility factors between the bud and root. With the advent of Gisela® dwarfing rootstocks for sweet cherry, in particular, and others such as MxM® and MaxMa®, and other new developments, it is possible to grow much smaller cherry trees that produce much earlier and more heavily. When you buy Dwarf cherries most likely they are on one of these. If they are identified as Semi-Dwarf, then they are likely to be on Mahaleb rootstock. We should assume that Dwarf means a size-controlling rootstock that must be planted at a shallower depth than a Standard or Semi-Dwarf cherry root.
As for peaches, nectarines, plums, prunes, and apricots, there are few truly dwarfing rootstock available, so almost all of these may be planted with the bud union one to two inches below the ground.
The Bottom Line: Planting too shallow is easier to correct than planting too deep.
Grandpa’s Orchard is shipping rootstock right now!
For more on rootstocks, you can also visit: graftingsystems.com