Soil and trees
A vital and often overlooked factor affecting the health of your trees and shrubs is soil. In fact, improving your tree's soil is very often the best possible thing you can do to help it thrive
Soil is not just dirt. Soil is an ecosystem where thousands of different organisms coexist, often competing, but often helping each other survive. Plants, animals, fungi, bacteria - all have forged lasting symbiotic relationships with other species at some point in their evolutionary histories. They rely on the benefits of these relationships through times of hardship. Soil also contains large numbers of mineral elements. The composition of these elements varies greatly from region to region which is one reason that some plants do well in certain areas, while others quickly die.
The tree in you
didn't evolve to grow in a mown yard next to a driveway. It evolved in a forest with all of the other organisms in that ecosystem. The soil of a tree's native habitat contains the right composition of minerals and the proper mixture of living things to enable the tree to prosper.
When a tree is planted in an urban environment, the soil is almost invariably inadequate for ideal growth. It lacks certain minerals, beneficial mycorrhizal fungi and nitrogen-fixing bacteria. Add to this the fact that most urban soils are also severely compacted and often polluted, you begin to see why something needs to be done.
Fortunately, there are steps you can take to ensure your trees and shrubs have the soil they need. The first step is regular fertilization. The second step is the addition of mycorrhizal fungi.
Mycorrhizae form when mycorrhizal fungi infect newly forming non-woody roots as shown here.
Mycorrhizae is a symbiotic relationship between beneficial fungi and plants. In exchange for sugars and simple carbohydrates, the mycorrhizal fungi absorb and pass on minerals and moisture required for the plant's growth.
Over tens of millions of years plants have developed this relationship to enable them to survive conditions of drought, extreme temperatures, and periods of low soil fertility. Because mycorrhizal fungi live in and around a plant's living root system, they effectively extend the root system deeper into the soil, allowing a plant to take in more nutrients. These organisms are a vital link in a plant's nutrient cycle.
In nature, mycorrhizal fungi are found on about 99% of plant species, but in urban environments, the poor, compacted soils often lack this essential fungi.
Almost all trees in urban settings will benefit from the addition of mycorrhizal fungi to the soil, but different types of trees require different fungi.