MYCORRHIZAL FUNGI

BY the Horticultural Staff at Stargazer Perennials

A mycorrhiza (mycorrhyzae or mycorrhizas, Greek for "fungus root”) is a mutualistic (mutually beneficial) association between a fungus and a plant. This mutualism occurs at the plant root level: Mycorrhizal fungi are soil-dwelling, root-inhabiting, symbiotic fungi that colonize the fine absorbing roots of more than 95% of the land plants in the world. Various species of these fungi colonize tree and other plant roots to feed on the photosynthates (sugars) of the plants. In return for sugars, the fungi extend ‘feeding tubes’ called mycelia far into the soil. The plant gains the use of the mycelium’s tremendous surface area to absorb mineral nutrients from the soil. Some forms of mycorrhizae can increase the absorptive surface area of root systems by more than 700% compared to non-mycorrhizal roots. In addition, the mycorrhizal association allows the plant to access all of the 15 major and minor mineral elements, many of which are in forms unavailable to a non-colonized plant. For instance, many gardeners are aware that phosphorous is an important nutrient that can become ‘locked up’ in the soil, and be unavailable to plants. This “phosphate sink” occurs because phosphate ions are tightly bound to iron oxides in many soils, and plant root systems cannot access this important nutrient. However, mycorrhizae are able to absorb and transfer this form of phosphorus to their host plants. Through their alliance with plants, mycorrhizae increase the tolerance of their plant hosts to drought, compaction, high temperatures, heavy metals, soil salinity and toxicity, and adaptability to extremes of soil pH.

So why does the average gardener need to know all this? Well, mycorrhizal fungi occur naturally in forest soils where the organic matter content is high. Unfortunately, most farm and garden soils do not exist in such an ideal state. Tillage, synthetic chemical fertilization, pesticide use, and low soil fertility will reduce or eliminate mycorrhizae. By amending the garden soil with copious amounts of rich compost and using only low impact organic fertilizers you can reproduce nature’s thriving ecosystem in your own landscape. Although we use endo-ecto mycorrhizal amendments in our nursery program, studies have shown that nursery pot culture is a tough place for mycorrhizae to thrive, so we recommend the addition of mycorrhizae spores after you have enriched your soil with compost and during planting. We make it easy, too! You can add mycorrhizae and organic fertilizer at planting time by using one of our organic fertilizers that are infused with beneficial bacteria and mycorrhizal fungi to allow rapid colonization of your garden soil. Our Down to Earth Bio-Live 5-4-2 for herbaceous plants or our Tree & Shrub 4-2-4 for woody plants are really exceptional products. We can’t recommend them highly enough: Try them out this summer and let nature do the gardening!

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