In many areas, fall is the perfect time to plant and transplant trees and shrubs. To ensure the best chances of survival, nothing can replace buying a healthy plant and digging a proper hole in well-drained soil. But now many gardeners and professional landscapers have another tool to lessen transplant shock mycorrhizae fungi.
These fungi often occur in the root systems of forest trees and shrubs. The fungi colonize the roots, increasing the plant's ability to absorb water and nutrients; at the same time, they feed on sugars from the plant. Fine strands called hyphae penetrate soil particles that plant roots can't reach. Mycorrhizae can protect plants from heavy metal toxicity and are often used on trees planted at mine reclamation sites.
Although these fungi occur naturally in healthy soil, they are often absent from low-fertility subsoils. Plants in poor soils in urban environments and new home developments, where all the topsoil has been stripped away, can benefit from mycorrhizae, explains Mark Starrett, researcher at the University of Vermont in Burlington. The fungi are not harmful to plants or animals, and typically you only have to inoculate once, at planting time, by mixing the fungi powder into the planting hole. For established trees or shrubs, sprinkle and lightly cultivate in mycorrhizae within the drip line.
Two types of mycorrhizae are available. Ectomycorrhizae are generally used on evergreen trees and shrubs and some deciduous trees, while endomycorrhizae are particularly useful on deciduous shrubs and citrus. Most products on the market are a combination of the two, so you're sure to get the correct type for your planting. However, plants of the Ericaceae family, including azalea, rhododendron, mountain laurel, and blueberries, do not benefit with either type.