Trees have been on everyone’s mind. Hundreds, maybe thousands, fell during the big windstorm on November 30th. People wondered whether the high failure rate was due, at least in part, to horticultural practices. Trees growing in parkways, receiving frequent, shallow irrigation, toppled over in the strong winds. Many of these trees had been subjected to root pruning during road and sidewalk repair. Surely these conditions resulted in much of the damage. Trees located next to houses and other buildings were watered on schedules better suited to the turf grass growing beneath them. In compliance with city regulations, many of these specimens received water several times each week for fifteen minute periods. The grass was green, but the trees grew shallow roots unable to withstand the nearly one hundred mile per hour winds.
It is possible, even likely, that under better conditions, fewer trees would have failed. In the next few posts, I will describe the ideal conditions for growing a beautiful, strong, long-lived tree beginning with selecting and planting new trees, moving on to caring for and training young trees, and finally, proper care for mature trees. I will try to include photographs of common, less-than-ideal practices, featuring both my own mistakes and others that can be seen in nearly any neighborhood.
Good, strong landscape trees start from the very beginning, with proper selection and care. Selecting a young plant that will eventually turn into a healthy mature tree requires the following conditions.
- Only trees with excellent form, both above ground and below, will be planted.
- These young specimens will started in the landscape either from seed (acorn, etc.), or at least transplanted when young, say no bigger than 15 gallon containers, with 5 gallon being a preferred size. The longer a tree is in a pot, the more time there is for root damage or stress to occur. Smaller trees often experience less transplant shock and usually catch up quickly with large, older specimens.
- The roots will be well formed, spreading out symmetrically, with no roots circling within the pot. If there is a young tap root, it will not have been cut or damaged. Trees often fail years after planting because they developed circling roots while still in relatively small nursery pots. These roots continue to grow in tight balls that never adequately anchor the trees, and eventually choke off water. They may fall in windstorms, or decline due to inadequate uptake of water and soil nutrients.
- The young “nurse branches” will have been left intact to feed the main stem resulting in a well-developed trunk with a nice flare at the base, as the tree matures.
- The new plant will show no sign of stress or disease.
- Only trees adapted to the local conditions – climate, soil type, water, exposure – will be selected.
In our ideal world, this perfect specimen will be planted in an ideal location.
|These sweetgum trees were planted beneath power lines and need frequent pruning by So Cal Edison resulting in unappealing trees with weakly attached branches.|
- It will be the right sized plant for its location so it will never be topped because there are power lines above, because it is “too big for the house,” or for any other reason.
- Its roots will have room to grow and spread.
- If irrigation is required, the tree will be watered according to its needs rather than the needs of nearby turf grass or tropical flowers. In general, it will be watered infrequently, usually once or twice a month when there is no rain, and deeply, soaking the soil to a depth of two feet or more for mature trees (p.84, CA Master Gardener Handbook).
Not only will our trees be perfect specimens when starting out, not only will they be placed in the ideal location, but also they will be planted in the way that gives them the best possible start.
|Crown of tree (place where stem starts
to flare out to roots) is buried – this
tree does not have a chance unless
this is corrected.
- The plant will be placed in a hole no deeper than the distance from the pot bottom to the crown of the plant. Ideally, the crown of the plant will be slightly above ground level when planted so the crown remains above the surface even if the soil compresses slightly. A very common cause of failure for newly installed trees is buried crowns. The trees may be planted too deeply, the soil on which they stand may compress, or soil may be piled up around the tree much later. When I see a dead tree, I always dig down to determine where the base of the tree is – that is, where the trunk flares out to form roots. This area, the crown, must never be covered with soil.
- The hole should be wider than the container that the tree was taken from. The walls of the hole may be roughened to make it easier for roots to penetrate the surrounding soil.
- No amendments will be added to the soil. The native soil will be placed back into the hole.
- The soil will be tamped down firmly so there is good contact between soil and roots, but not packed down so hard that the roots are deprived of water and air.
- A water basin may be created around the plant to direct water to the root area. This basin will be checked periodically and removed if rains or irrigation leave the tree standing in a puddle. If this occurs, either irrigation will be modified so that water can penetrate the soil, or in the case of heavy rains, the berm will be removed.
- Since a perfect specimen was selected, the young tree is unlikely to need staking. If there is a nursery stake, this will be removed during planting and the hole filled in. If staking is required due to other conditions, such as high winds or heavy public use, two stakes at the correct height, with flexible webbing will be used. The stakes will allow the plant to move so it can develop a strong root system, and an adequate trunk caliper and taper, with a good flare at the crown. Stakes will be checked frequently to ensure that there is no damage to the trunk and to confirm that they are still supporting the tree properly. They will be removed as soon as possible, preferably during the first or second year of growth.
- The new specimen will be watered in carefully so that the soil is wet but not sodden. The water should soak into the root ball and the surrounding soil. Water will be applied again after the first application soaks in.
- Organic mulch can be used to moderate soil temperature and reduce water loss, though the crown area will be kept clean of soil and mulch.
Trees selected and planted this way are given an excellent start. In the next few years they require careful attention to make sure their roots leave the planting hole, penetrating the surrounding soil. The following tips will help the new plant during this period of establishment.
- Before the first hot spell, feel around the root ball to check for large air pockets. These can form if the nursery soil had a lot of organic material that decomposed after planting. Gently, but firmly, press the soil to fill these holes. If you need to add soil, use the nearby garden soil.
- Again, mulch can help these tender plants through hot weather, though it is critical that the crown remains clean.
- The young trees should be watered regularly so that they do not dry out, but make sure that the soil in and around the root ball is not sodden. When soil is completely saturated there is no air available for the roots, and the soil can become compacted. Furthermore, disease-forming organisms thrive in hot, wet conditions, especially when there is little air present (anaerobic), resulting in root rot or other plant diseases. Water well, water thoroughly, and then do not water again until the soil begins to dry out. It is best to water before a young plant shows signs of drought stress.
Young trees often require pruning to develop into well-structured mature specimens. In the next post, I will describe pruning practices that can prevent future problems. These include removing suckers and crossed branches, selecting scaffolding limbs, and protecting and encouraging the growth of a strong and straight lead branch.
Iowa State University, Forestry Extension
International Society of Arboriculture (Trees are Good website)
USDA Forest Service
University of California
ANR (Agriculture and Natural Resource), Lawn and Garden Catalog
Cooperative Extension, Center for Landscape and Urban Horticulture, Planting
Cooperative Extension, Master Gardener Program, The California Garden Web, Landscape Trees
California Master Gardener Handbook, Dennis R. Pittenger, Ed. 2002. Berkeley, UC California.
Planting and Care of Landscape Trees, Part 1, Pam Bone (90 min. video)
Planting and Care of Landscape Trees, Part 2, Pam Bone (90 min. video)
Urban Forest Ecosystems Institute