Fertilizing Transplants

By Michael J. Kernan, Ph.D.

Mycorrhizal fungi grow out from the root and form an extensive network of absorbing strands that service the water and mineral needs of the host plant.

Newly planted B&B or bare root trees or shrubs face one important problem ?EUR??,,????'??? they always suffer from a severely reduced root system. Under normal circumstances, a tree?EUR??,,????'???s roots will grow out from the trunk and extend well past the drip line. Absorption of water and minerals occurs in the upper 8 to 10 inches of soil. However, B&B or bare root trees have a minimal root ball. This reduced root system has the daunting task of supplying the entire canopy with its total water and mineral nutrient needs. As a result, new transplants often need special care (such as frequent watering) to survive the resulting period of transplant stress, until the root system catches up, and occupies enough soil to meet the needs of the canopy.

Fertilizers containing high levels of available nitrogen tend to promote foliar growth at the expense of root growth. As a result, the burden on the limited root system increases. This can exacerbate transplant stress, resulting in wilting and dieback. Therefore, you should select treatments that support root growth or improve root function without promoting top growth. Here are some examples of such treatments.

Low Nitrogen Fertilizers

In most cases, it is best to avoid fertilizing a new transplant with high levels of soluble nitrogen during its first year of growth.

This allows the roots system to catch up and achieve a size capable of handling the larger canopy. However, nitrogen fertilizers can be applied to a new transplant, if you are careful to supply N at low levels and/or in slow-release forms. That way, nitrogen will become available at rates too low to promote rapid foliar growth.

Transplant stress occurs when the limited roots cannot absorb enough water to support the needs of the canopy.

Mineral Treatments

Mineral treatments provide various minerals that plants require other than N, P, and K. These include magnesium, sulfur, and various micronutrients like iron, manganese, and to a lesser extent, boron, zinc and copper. Various products are formulated to contain several of these minerals together. Be sure to select products whose micronutrients are formulated to be soluble throughout a broad range of soil pH.

Mycorrhizal Fungi Innoculation

Treating a new transplant with mycorrhizal fungi is an ideal way to rapidly aid root function. These beneficial fungi colonize the roots, setting up a base of operations. From there, the fungi develop an extensive network of absorbing strands that grow out into the soil to find and absorb water and minerals to be pumped back to the roots. Mycorrhizal fungi act as roots of the roots, significantly increasing their host plants?EUR??,,????'??? ability to extract water and nutrients, even from droughty or nutrient deficient soils. Be sure to select mycorrhizal fungi products from reputable companies with product labels that fully disclose the contents, especially the number of spores of each species of fungi. Also, make sure the label has an expiration date, since fungi are alive and will not live forever. Using a product that is too old to contain any living spores makes no sense at all.

Tree Facts

25: Percent or less, the amount of root systems of trees and shrubs dug from the wild or established landscape plantings that remain intact when transplanting.

Source: North Dakota State University Extension Service