Tree Care is "Hot" Topic at 2011 Summer Short Course

The resulting recommendations have shown positive impact on nursery and landscape practices regarding tree planting and maintenance. Bringing this caliber of research-based information to green industry professionals and home gardeners is the core of Penn State Extension’s mission.

The first session focused on roots – how roots grow in nature versus how they grow in production nurseries, especially container-grown trees. In nature, roots grow straight out from the trunk without the circling and bending seen so often with container-grown trees.
When trees are potted up into larger containers without breaking up the circling roots, they frequently grow into stem girdling roots that shorten the life span of the tree while posing a risk to people and property when the tree fails. Dr. Gilman’s research shows that shaving the circling roots before repotting – a process that takes very little time – reduces the chance of those roots becoming girdling roots to a minimum. Special containers made with a series of slits around the sides can diminish root growth on the outside edge of the root ball, reducing the need for such root pruning.

The second session focused on pruning young trees so they are structurally sound and less likely to fail once they are planted out in the landscape. Dr. Gilman recommends training saplings to a central leader – even those trees that will not maintain a central leader at maturity. Taking time to prune young trees will eliminate co-dominant stems and steep branch attachments, resulting in more attractive, healthier trees. Making those cuts when wayward branches are small creates small wounds that heal quickly compared to the wounds that result when larger, more mature branches must be removed to correct defects.

Another interesting finding of Dr. Gilman’s research is the importance of maintaining temporary branches low on the trunks of young trees. The added leaf area allows increased photosynthesis, permitting trees to grow faster and develop adequate trunk caliper and appropriate taper. Those branches are typically removed 6-12 months before sale to the end user.

The final session focused on proper planting and management in the landscape. According to Dr. Gilman, when planting a tree, start by making sure the root collar (the uppermost roots) is in the top two inches of soil in the root ball, whether you are planting a container grown or balled in burlap (B & B) tree. If necessary, remove excess soil until you find the root collar. Dig the hole so the root collar will be even with the soil surface when it is planted, but no deeper.  Make sure the soil in the bottom of the hole is firm so the tree does not settle too deeply. Use a spade or a rototiller to loosen the soil in an area around the planting hole that is three times the size of the root ball to ensure strong root growth and quick establishment. Before placing the tree in the planting hole, cut away any roots that are growing in a circle or doubling back over the root collar to avoid problems with girdling roots later in the tree’s life.  Backfill with the soil you removed when digging the hole, watering it in to minimize air pockets. Build a berm of soil or mulch around the circumference of the root ball to hold water so it soaks into the root ball.

Mulch the area of loosened soil, but do not place mulch over top of the root ball. Start mulching at the edge of the root ball, using two to three inches of mulch to cover the area of loosened soil. That is sufficient to conserve soil moisture and moderate soil temperatures. Mulch over top of the root ball can be problematic in that mulch can become water repellent when it dries out. Small rain events wind up just wetting the mulch, but do not get down to the roots where water is needed. Also, mulching over top of the root ball encourages trees to root up into the mulch. These roots can grow into girdling roots over time.

Once the tree is planted, apply three gallons of water per inch of trunk diameter to the root ball two or three times a week for the first growing season. As the tree becomes established, apply more water at one time and water less often. In the second year weekly irrigation and every other week in the third year should be sufficient.

Finally, continue pruning the young tree to maintain structurally sound growth. Cut back or reduce stems that compete with the central leader to encourage strong growth in the central leader.

More information on Ed Gilman’s research and recommendations can be found at: http://hort.ufl.edu/woody/