Planting depth of trees -- A survey of field depth, effect of deep planting and remediation.

摘要

A series of surveys and experiments were conducted on the deep planting of nursery/landscape trees. To learn about the frequency of the condition, nursery trees were surveyed for planting depth before and after harvest. To determine the effect of deep planting on tree growth and development, trees were grown with excess soil over their root system in a field nursery and in containers. In an attempt to remedy the malady, deeply-planted landscape trees were treated with air excavation.In a survey of Ohio nurseries and tree brokers, an average of 6.1 cm (2.4 in) and 8.6 cm (3.4 in) respectively of excess soil was found over the root systems of trees. These amounts exceed industry standards. In the nursery survey the amount of soil on the root system of nursery trees decreased during production from 6.6 cm (2.6 in) in year one to 5.3 cm (2.1 in) in year three. The broker survey found that trees raised from cutting have more soil over their root system [9.9 cm (3.9 in)] than trees propagated by either budding or seed both of which were 7.9 cm (3.1 in) too deep in the soil profile.In a nursery test, Autumn BlazeRTM red maple ( Acer x freemanii) and 'Prairifire' crabapple (Malus sp.) were planted at depths of 0 cm (0 in), 15 cm (6 in) or 30 cm (12 in). Both species showed a limited response to the deep planting treatments. When harvested during their third year of growth both species planted at the 15 cm (6 in) and 30 cm (12 in) deep planting depths had two root systems. The first root system was the original at either 15 cm (6 in) or 30 cm (12 in) deep, while the second was at the soil surface. The second root system was believed to be the plants adaptation to deep planting and may be an explanation for the lack of response to the deep planting treatments.Autumn BlazeRTM red maple was grown in soilless media in containers at planting depths 0 cm (0 in), 15 cm (6 in) or 30 cm (12 in). The trees showed a limited response to the deep planting treatments. As with the field nursery test, trees initiated a second root system at the media's surface.Landscape trees with excess soil over the main lateral roots (root flare) were treated with root crown excavation (RCE) using air excavation. Fifty per cent of sites failed to show any influence from RCE on tree growth. The trees included shingle oak (Quercus imbricaria Michx.) median street trees, blue spruce (Picea pungens Engelm.) park trees and honeylocust [Gleditsia triacanthos L. var. inermis (L.) Zab.] parking lot island and street trees. Twenty five per cent of the remaining sites that included maple (Acer spp.) park and street trees showed a detrimental effect from RCE. The other 25% of the sites which included ash (Fraxinus spp.) park trees and lacebark elm (Ulmus parvifolia Jacq.) street trees showed a positive effect from RCE.