Apr 18, 2015

Spring is one of the best times to fertilize.

Why fertilize? Because trees need nutrients to grow and thrive. These nutrients are usually found within the soil but urban soils are notoriously deficient. A lack of essential nutrients will result in an underdeveloped tree, and ultimately an unhealthy tree with a weak immune system, resulting in being more susceptible to disease and infection.

Trees growing in nature generally have access to all the minerals they need to survive and grow. The tree’s roots take the nutrients from the soil and use them for root development and for guarding against disease and infection.

Trees are often under significant stress due to all manner of environmental situations, including lack of moisture, physical damage, soil compaction, depleted soil and competition from other nearby trees. If a tree is growing poorly, due to the common factors discussed above, it will usually show some – or at least one – of these symptoms:

Yellow or green leaves

Leaves with dead spots

Small leaves – or leaves which are smaller than normal

Stunted twig growth

Wilted foliage

Conducting a soil test can pin down exactly what fertilization is necessary but because it is time consuming, and because most soils in Atlanta test the same, it is seldom performed. Without testing, assessing new shoot growth is a guide. Look for the symptoms listed above. For instance, generally speaking, if growth is six inches or more, then fertilization might not be required – if it’s between two and six inches, however, it’s probably advisable.

If any of the trees in your yard or garden exhibit these tell-tale signs, especially with below expected shoot growth they will almost certainly be lacking vital nutrients. Nutrients required by all trees can be divided into two groups: macronutrients and micronutrients. Macronutrients include nitrogen, phosphorus, potassium, calcium, magnesium and sulfur; micronutrients include iron, manganese, zinc, copper, and chlorine.

Fertilization is beneficial year round but results are most visible when tree roots are growing – especially in spring.

There is of course more to the story than this blog presents, including pH of soils and fertilization methods. Your arborist will consider the complete picture when assessing your trees.

Other related issues include soil compaction and mulching, both of which can have profound effects on tree health.