Fertilizing is an important step in the care of an elm tree. Fertilizing helps an elm tree grow properly, sustains the proper color of the leaves and prevents the early loss of leaves. Because fertilizing plays such a vital role in a tree's overall health and development, it must be done at the right time with the right type of product.
According to the University of North Carolina Extension, fertilizer for shade trees, such as elms, should have a high nitrogen content but must be a slow-release formula. Carefully consider the ratio of nitrogen to other nutrients, as the amount of nitrogen should be at least double.
Type to Avoid
According to treehelp.com, general-purpose fertilizers intended for use on lawn and other garden plants should be avoided on elm trees. Many of these varieties release a large amount of nitrogen quickly and can cause devastating structural damage to the tree, specifically weak growth. Consequently, a tree in such a weakened state may attract pests that transmit Dutch elm, a fugal disease.
Treehelp.com suggests applying a fertilizer to an elm tree at least once a year; twice is acceptable depending upon the needs of the tree. Having the soil tested for deficiencies will also help to gauge whether the tree needs to be fertilized once or twice a year.
Where to Apply
Because the elm tree is a shallow-rooted species, fertilizer must cover the estimated root spread. This compensates for the general fertilizing application near the absorbing roots.
When to Apply
According to the University of Missouri Extension, elm are best fertilized in the late fall, but before the soil freezes in the winter. If fertilized at this point, the soil's temperature is still adequate to absorb minerals.