By Nathan Lawrence, Owner of the Good News Tree Service, Inc. in Wilsonville, OR since 1985 — ISA Certified Arborist • ISA Tree Risk Assessment Qualified • State of Oregon Licensed • Commercial Pesticide Applicator • OSU Master Gardener
The following information and recommendations pertain to the northern Willamette Valley areas of western Oregon.
Planting the right tree in the right location will help to minimize plant stress (both biotic and abiotic), pests and mortality, thus ensuring better tree performance for years to come. This is a wise use of resources, economical, good for the well-being of the community and for the local environment and the earth in general. This also means that fewer chemical pesticides will be required in caring for the tree, which is a good thing for everyone and everything.
To accomplish these goals requires intentional planning and tree planting strategies. Prevention is the best medicine! Property owners cannot afford to pay someone simply dig a hole and drop a tree in it, and then walk away after the tree planter has collected their money and moved on. Garbage in garbage out! If the tree was not planted with intentional forethought with an eye on long term tree survival, it is likely the tree will under-perform, require expensive (often chemical) treatments and may even die. If the tree is planted with strategic and intentional forethought, and then properly cared for subsequently, it will be more likely to perform healthily for generations to come
The following are some things to consider before planting a tree on a site.
It is essential first to determine the soil volume of the planting area, so that the appropriate tree can be chosen for that specific site. The smaller the soil volume, the smaller the tree (at mature size) that can be planted in that area. Conversely, the larger the soil volume, the larger the tree (at mature size) that can be planted. I recommend that the tree size–soil volume ratio be based on the study entitled, “Our Recommended Soil Volume for Urban Trees” by Jim Urban et al at https://www.deeproot.com/blog/blog-entries/our-recommended-soil-volume-for-urban-trees-2/. If a tree doesn’t have the proper soil volume, its roots will not be able to uptake the amount of soil moisture and nutrients they need to be healthy, nor will they be able to anchor themselves sufficiently against wind storms.
Soil Type, Texture and Structure
Next, we must conduct a soil test to 12 inches deep to determine soil type, texture and structure, so that the right tree is planted in the soil type that it prefers. This involves determining the approximate proportion of sand, silt, clay (and loam, which is a combination of the previous three soil types). This can be done via the standard jar test. This involves placing a soil sample with water into a Mason jar, shaking and then letting everything settle out in layers overnight or longer to determine the percentage of sand, silt and clay. Since sand is heavier, it will be at the bottom followed by silt and then by clay on top.
Soil structure involves knowing soil particle size to be able to determine moisture retention and the permeability qualities of the soil in question. Also, if soil is compacted, air space may need to be added through air spading, loosening the soil mechanically or by hand. Soil compaction can be assessed by how easily a pointed rod or soil sampling tool penetrates the soil down at least six to eight inches. If soil is compacted, roots will have a harder time penetrating, because pore space is limited, and so will be the air and water that will fill those pores. This will not only hinder root growth, but limit air to the roots, which is necessary for respiration or turning carbohydrates into sugar or energy for root growth. Compacted soil also hinders the roots from uptaking water and mineral. Compacted soil also reduces soil pore space, which hinders microbial activity, which depend on soil and water for their metabolic processes All of these functions are necessary for healthy soil, which in turn promote plants.
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