Lauterbach: Feed your garden the nutrients it needs

Special to The Idaho StatesmanMarch 14, 2014 

Healthy plants are vigorous, firm and the shade of green they're supposed to be, bearing beautiful flowers or tasty fruits or vegetables.

To grow their best, they must have been planted in healthy soil. That is, soil that has a vigorous living population of bacteria, protozoa, nematodes, arthropods and other micro-organisms plus beneficial fungi such as mycorrhizae.

Mycorrhizae, by themselves, are for sale, but are costly and invisible, so you've got to trust your vendor and his supplier.

It's much easier and more cost-efficient to add those fungi with your fertilizer.

Some fertilizer bags have been updated to reflect newly spread knowledge about what really feeds plants. Several, including Dr. Earth, E.B. Stone, Bio-Tone and others, are including mycorrhizae in their fertilizers. They and some other compilers also are adding trace and/or minor elements necessary to plants.

Read the labels. If other nutrients are in the bag, the label will tell you so.

It's a good idea to be cautious about over-fertilizing your soil with micronutrients. If they're included in your regular NPK fertilizer, don't add more. I don't think you can overdo on mycorrhizae, but they're probably inappropriate and unneeded in container plantings.

Mycorrhizae spores are ubiquitous in healthy soils, and after plants are added to that soil and soil conditions are right, they're prompted to develop into a mycelium that can partner with those plants. Most plants will struggle until mycorrhizae get established, so adding it in your first fertilizer will give your plants a jump start.

Some of these symbiotic fungi (mycorrhizae) penetrate roots, where they feed nutrients and water to the plant while being fed excess sugars formed by the plant’s photosynthesis. Another kind coats roots.

This mutually beneficial partnership does more than just feed plants and the fungus, though. (Since mycorrhizae fungi, like mushrooms, don’t contain chlorophyll, they cannot feed themselves.)

Mycorrhizae also build larger, healthier root systems and healthier plants, reduce plants’ need of water and fertilizer, increase drought tolerance and create more stable soil (less erosion) while protecting host plants against some soil diseases and pathogens (infectious agents).

The strands of these fungi also help form glomalin, which clumps particles of soil together, leaving air spaces that provide oxygen to roots. They also help sequester carbon in soil.

Plants can grow without these fungi, but most are more apt to thrive and produce if they have developed that partnership.

Since these beneficial fungi need roots for their food supply, it's a good idea to keep your gardens alive as close to year-round as possible. I cut off tomatoes and most other plants about an inch above the soil line, and by the following spring, little is left of the roots. Part of their decay may have been feeding mycorrhizae.

To preserve this invisible web in soil, it's best to dig or trowel as little as possible, avoiding tearing the hyphae (strands of mycelium) apart.

Rototilling is especially damaging. Fast-acting non-organic fertilizers, especially those loaded with phosphorus, are detrimental to the existence of mycorrhizae, and may destroy it and other microbial life in your soil.

Vegetable garden plants that do not need mycorrhizae are the Brassicas - cabbage, Brussels sprouts, collards, kale, etc. - and mustards, radishes, etc. Other plants, including trees, do need these fungi.

Send garden questions to or Gardening, The Statesman, P.O. Box 40, Boise, ID 83707.

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