Certain rules in horticulture don’t change. Tomato plants freeze easily at 32 degrees, a constant not likely to change anytime soon. Some things do change, though, like tree planting recommendations.
When my wife, Mary, and I embarked on our nursery-greenhouse ownership adventure 35 years ago, the planting guidelines for customers who purchased trees were different than today’s most recent recommendations. Some planting practices that were common for decades cause problems as trees grow. We still see trees declining from being planted too deeply and with circling roots left intact.
Hopefully things are changing, but back then, trees were often planted deeply within their nursery pots so they wouldn’t pop out in the first strong wind, and buyers were told to plant the rootball a little deeper than in the pot — all of which result in trees being planted too deeply at each stage. This too-deep planting scenario causes many trees to fail after five to 15 years.
When potted trees were planted into the landscape, it was also believed that minimal root disturbance would lessen transplant shock, and many rootballs were planted intact, even though roots were tightly encircling. After ten or 15 years, these circling roots continue their pattern, often strangling, or girdling, the tree as roots and trunk both expand.
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The following tree planting tips were developed to prevent the problems of too-deep planting and circling roots, based on recommendations from North Dakota State University Extension Forester Joe Zeleznik and Extension Horticulturist Esther McGinnis.
How to plant a tree
- The hole doesn’t need to be very deep, but must allow the “root collar,” also known as the trunk flare, to be at ground line or slightly higher. The trunk flare is the widened part, where trunk meets roots.
- The hole should be about twice as wide as the rootball.
- If the soil is heavy clay, rough up the sides of the hole to prevent glazing.
- Always keep the roots moist during transplanting. If the roots dry out, then the tree will die.
- Place the tree in the hole at the proper depth. This may involve removing soil from the top of the rootball if it was planted too deeply in its pot earlier in its development. You might need to add soil in the bottom of the hole to ensure that the tree is not planted too deeply. Look for the uppermost main root branching from the trunk. This first “flare root” should be just below soil surface when planting is finished.
- Remove any circling roots on the edge of the rootball, which might require extreme measures, such as cutting away the outer inch of soil and roots from the rootball, or pulling roots outward from the circling mass. If circling roots are left, the tree likely will have structural problems in the future and will need to be removed long before it reaches maturity.
- Backfill the hole with the original soil that was removed. Break the soil into smaller clumps if possible to allow the roots to extend into the new soil more easily. Other soil amendments do not provide any benefit to the tree and are not needed.
- Staking might be needed for one year, or two at most, and should be installed to allow some limited movement of the trunk while keeping it straight.
- Water the tree after backfilling to remove air pockets from the soil and improve root-to-soil contact. Water twice a week during the first month after transplanting and once a week during the second month, and then cut back to once every 10 to 14 days.
- Mulches, such as shredded bark or wood chips, minimize competition from weeds or grass, retain soil moisture, prevent extreme soil temperatures and prevent lawn mower and trimmer damage.
Fall planting is highly successful and gives a head start versus waiting until next spring. Roots continue to grow until soil temperatures cool to below 40 degrees, and if trees are planted by Sept. 30, they’ll have a month to develop new roots.
Don Kinzler, a lifelong gardener, is the horticulturist with North Dakota State University Extension for Cass County. Readers can reach him at firstname.lastname@example.org or call 701-241-5707.