Keeping Your Tree Soil Healthy

A tree is as healthy as the soil it sits in. And yet, a trees soil is often overlooked. So what can you do to improve your tree's soil?

To start, soil is not just dirt.  You can consider soil as its own ecosystem as it really is. There are thousands of different organisms that coexist within soil, often competing, but often helping each other survive.  These include plants, animals, fungi and bacteria - all which have forged lasting symbiotic relationships with other species at some point in their evolutionary histories.  These organisms 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. 

When trees are planted in areas that are often depleted of minerals and needed organisms is when the most attention needs to be placed on supplementing the soil. Such places often include areas that have been over planted already or urban environments. Places that are over planted often pull many of the nutrients from the soil, especially if they are similar trees requiring the same organisms and minerals. As for urban environments, the soil is often inadequate due to lacking certain minerals along with beneficial mycorrhizal fungi and nitrogen-fixing bacteria. 

To improve your soil, the first thing you can do is to fertilize. When fertilizing, remember that you are trying to mimic a soil's ideal condition. An easy way to replenish your soil is with compost. If you don't want to pay for compost, just allowing your leaves to remain on the ground instead of raking them up, will allow these leaves to break down and return their nutrients back to the soil. If you prefer to purchase your fertilizer or don't have leaves you can just allow to crumble into the ground, look for fertilizers made up of macronutrients (Nitrogen, Phosphorus, and Potassium) and micronutrients (such as Iron, Magnesium and Manganese).  These minerals all have different effects on the growth of a tree and different trees need different formulations. 

A good time to fertilize trees in most Northern temperate climates is from fall to mid-spring.  At these times the tree's roots take the nutrients from the soil and apply them to important health-promoting functions such as root development and disease resistance, rather than simply putting out new growth. You can also fertilize during the growing season which can help your tree overcome mineral deficiencies and fight off infections.  If you are fertilizing in mid- to late summer, avoid formulations high in nitrogen as this will just promote weak, new growth that may be easily damaged in the winter.

When applying fertilizer, place them where you think they best will be taken up by the tree's roots.  In general, the roots extend well beyond the outer reach of a tree's branches. 

The fertilizer must also be placed underneath the roots of any competing plants such as grass or other ground cover.  Spreading granular fertilizer on the lawn might make your grass greener, but it will likely not help your tree.

The second step to improving your soil is to add mycorrhizal fungi.   In exchange for sugars and simple carbohydrates, the mycorrhizal fungi absorb and pass on minerals and moisture required for the plant's growth. 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 fungi.

Soil takes time and management, but by practicing a few practical necessities, your trees can continue to become stronger and healthier.

Andrew Johnson is the owner of Central Texas Tree Care, a leading tree service provider in Central Texas (Travis County and surrounding areas) offering services such as pruning and removals, cabling and bracing as well as arborist reports, diagnostics, pest management, fertilization and Austin tree service trusts. For more information please visit http://www.centraltexastreecare.com.