Written by Brent Holtz, UCCE San Joaquin County
One of the worst things that can happen to young trees from nurseries is that they are planted to deep. Sometimes they are initially planted at the right height, but then a berm is thrown up around the trees and their crown (the graft union between the scion and rootstock) is covered with the soil from the berm. I saw many diseased trees last spring that had Phytophthora root and crown infections and every one of them had their graft union below the soil line; sometimes the union was more than six inches below. If you are planting or replanting, trees should be planted high on small mounds as shallowly as possible. Planting depth after settling should be no deeper than in the nursery, and the graft union should always be well above the soil line.
Try to follow some of these planting tips:
1. Dig a hole deep enough so the roots are spread out and not cramped,
2. Plant the trees so that the nursery soil line is above the current soil line,
3. Plant the highest root a little above the soil line and then cover it with extra dirt, and
4. When planting allow for 3-6 inches of settling in the planting hole.
I have never seen trees die from being planted too high, but I have seen many trees killed by being planted too low. This is especially true in heavy soils with a high clay content. These soils have slow water percolation, drain slowly, and remain saturated longer than well drained sandy soils. The mound around the tree trunk forces excess water to drain away from the tree, thus reducing the length of time the crown is exposed to excess surface moisture. Saturated soil conditions can occur at plating if the trees are irrigated too heavily, or when a high rainfall winter and spring occur. Some orchards survive years before a wet spring kills trees that settled too deep or had their crown covered with a berm. Plant the tree right the first time!
After making a strong case for planting the trees high, there is one exception. If you are planting on Marianna 2624 plum rootstock you should plant your trees the same depth they were planted in the nursery. With this rootstock, planting trees too high will cause them to sucker from the roots. Marianna 2624 is fairly resistant to Phytophthora and it can also tolerate excess soil moisture better than other rootstocks.