Fall is the time many folks plant trees to give them time to get established before the growing season starts the following spring.
By following a few guidelines, young trees have a greater chance of prospering, according to Kelly Jackson, the Extension Service horticulturalist in Christian County and an ISA Certified Arborist.
“Trees are my passion,” Jackson said during a presentation, “Why Trees Fail to Thrive,” to a few dozen Henderson Garden Club members and others at the Henderson County Extension Expo on Sept. 5.
“Trees are kind of like the foundation of a landscape,” he said. “We want to make sure they last.”
Among highlights in Jackson’s presentation:
Species selection: “You have to spend time more purposefully” in selecting a tree that is likely to thrive both in our climate and in your yard, Jackson said. “It’s not always the best practice to go to a (big) box store” and buy whatever they have in stock.
A good first start is to select a species that is rated for our winters.
One thing that has changed is the warming climate. In November 2023, the USDA released its updated plant hardiness zone map, which provides guidance to gardeners and landscapers about what species to plant based on 30-year records of winter temperatures.
The previous hardiness map, released in 2012, placed Henderson in Zone 6b based on annual coldest temperatures averaging between 0 and minus-5 degrees from 1976 through 2005.
Now, Henderson is in the slightly warmer Zone 7a because annual coldest temperatures averaged between 5 degrees and 0 from 1991 through 2020.
But Jackson advised selecting trees that can withstand Zone 6b winter temperatures just to be safe. “All it takes is one winter” with frigid temperatures to compromise or possibly kill a tree, he said.
Careful selection of a particular species is also beneficial. For example, Jackson said willow oaks and swamp oaks do well here, but “pin oaks have problems in our area.”
Location: In addition to choosing a hardy species, select a tree appropriate for your location.
For example, Jackson said Japanese maples will benefit if they have some shelter from full sunlight.
Some plants, such as junipers, “are very picky and can’t tolerate wet soils” while cypress trees thrive in wet soil or even standing water.
Black gum trees (not sweet gums, which grow sticky gum balls) “can take the worst of the worst” soil conditions, Jackson said.
Avoid planting fruit trees in low areas that create “frost” pockets that can kill fruit buds in early spring.
Nutrients: It’s wise to take a sample of soil from the planned planting site to the Extension office to have it analyzed. If your soil is low in magnesium, iron or phosphorous, there are measures that can be taken to correct it. A pH test of the soil’s acidity can also be helpful.
Planting: A mistake many people make is planting a tree too deep. “It’s probably the No. 1 killer of plants in the landscape,” Jackson said.
“Roots have to have access to air,” he explained. They can slowly suffocate if planted too deep.
“The root collar” — where individual roots join the main trunk — “should be visible at the base of the tree,” Jackson said.
The hole should be two to three times the diameter of the root mass, but no deeper. “You want it wider, not deeper, than the root ball,” he said.
Trees can be harmed or killed by girdling, when the roots grow in a circle instead of outward from the trunk. This might be because a container-grown tree became rootbound. Girdling roots should either be trimmed or pulled from the root ball and spread out when the tree is planted.
A lot of soil here is heavy with clay. One option is to mix organic material — mulch, aged manure, compost or other material — with the soil dug from the hole.
If your location has especially compacted clay soil, one option is create a sort of plant bed by tilling organic material into a wide area around where the tree will be planted.
“The ideal (soil) is 50% something — soil or sand — and 50% nothing: air,” Jackson said.
Mulching: Mulch is a great way to preserve soil moisture, ward off weeds and keep mowers and string trimmers from the trunk of the tree.
But Jackson said to apply only two to four inches of mulch, and don’t let it touch the trunk. “Wider is better,” he said.
Watering: A tree will need regular rain or watering in the days, weeks, months, even years after planting.
Frequent but shallow waterings will do more harm than good. Jackson recommended using a soaker hose to provide a long, slow, deep watering. Be sure the hose encircles the tree beneath the drip line, or its furthest branches.