Mycorrhizal Fungi in the Organic Garden

As a gardener learns the benefits of growing vegetables and flowers using organic methods, it becomes increasingly apparent that soil is at the heart of every garden endeavor. On the surface, soil seems like a simple concept. However, the more one learns about the importance of soil, the more it seems there is to learn about its complexity.

Soil is comprised of both organic and inorganic compounds. Gardeners can manipulate minerals, along with decaying plants and animals, to produce varying results. Yet, there is a living component to the soil. Beneficial mycorrhizae fungi constitute part of the living matter in healthy garden soils.

What are Mycorrhizae?

Mycorrhizae are a group of naturally occurring fungi that have a symbiotic relationship with plants and trees. The fungi send out thread-like growths to the soil, where they extract nutrients for themselves. The fungi pass these nutrients on to roots, which in turn support the fungi by providing them with nourishing fluids.

How Do Mycorrhizal Fungi Help Plants?

When gardeners attempt to reproduce the growing conditions present in natural soils, they face the enemies of healthy soils: pavement, polluted runoff, pesticide residue, and inferior topsoil turn vibrant soils into lifeless deadpan. The reaction of garden plants in these conditions is increased susceptibility to disease, decreased nutrient uptake, and decreased drought resistance.

Encouraging a healthy mycorrhizae fungi population, whether naturally or through inoculation, can boost plants’ immune systems. The fungi can help the plants’ uptake of phosphorus in the soil, and the increased surface area of the roots increase plants’ ability to draw water from parched soils.

Increasing Mycorrhizal Fungi Naturally

The best way for organic gardeners to nurture the natural mycorrhizal fungi population in the soil is to add compost to the garden. Planting cover crops and minimizing chemical pesticide and fertilizer use also encourages mycorrhizal populations.

Using Mycorrhizal Inoculants

Organic gardeners tending a new plot of earth in a suburban landscape may be impatient to wait the two to three seasons necessary to build a beneficial mycorrhizae population with compost. Other gardeners growing sensitive crops like citrus, melons, or grapes recognize the need to ensure mycorrhizal symbiosis. These gardeners can consider commercially available mycorrhizal inoculants.

Commercial suppliers offer named varieties of mycorrhizal spores that gardeners can use to help plants utilize the nutrients in your organic fertilizers. Some mycorrhizal products are used as a seed drench, others are most effective when applied directly to the soil. Gardeners should speak to their supplier about the crops they intend to grow before purchasing, and then follow manufacturers’ directions about whether to use named fungi varieties or an all-purpose product.

Sources:

Department of Crop and Soil Sciences at Penn State

Wisconsin Integrated Cropping Systems Trial Project