We’ve all heard that classic organic gardening mantra, “Feed the soil, not the plants.” But what does that mean exactly, and who is it I’m feeding? Can’t I just dump on some Miracle Gro, like the infomercial tells me? No, you can’t—not if you want to grow like a Boss.
Aside from the rock and mineral particles, water, air and organic matter in healthy garden soil, we find an astounding amount of life. A level of intelligent interaction exists among these subterranean soil citizens that makes Wall Street look like Sesame Street. And perhaps nobody on the planet understands these players and their game better than Dr. Elaine Ingham.
The author of the US Department of Agriculture’s Soil Biology Primer, former chief scientist at the nonprofit Rodale Institute and founder of Soil Foodweb, Inc., Ingham is a seasoned professor, researcher and soil benefactor. Her work has propelled to a new level our scientific understanding of the dynamic roles played by microbes in the soil.
I recently had the pleasure of having my mind blown via telephone while speaking with her in anticipation of her end-June workshop in Boulder, Utah.
Your work revolves around the “soil food web.” Tell us what that means.
The soil food web is comprised of all the organisms that do the jobs in the soil, from building structure to protecting plants against diseases, pathogens and pests. These organisms will take nutrients out of the sands, the silts, the rocks and the clays, and make them available to plants.
One thing people don’t realize is that all of the soils on this planet contain all of the nutrients to grow plants. There is absolutely no need to put down inorganic [synthesized, chemical] fertilizers if you have all of the bacteria, fungi, protozoa, nematodes and microarthropods that your plant requires. Doing so will actually harm the organisms in the soil.
Every inorganic fertilizer is actually a salt, and kills the beneficial organisms. You’re destroying the system that nature put together long before humans came to the planet, the system to cycle nutrients and make them available to your plant.
The proper balance of all of these together—the beneficial bacteria, fungi, protozoa, nematodes, microarthropods, earthworms and all of the other life that lives in the soil: That is what I mean by the soil food web.
One thought that stood out to me from the book Teaming with Microbes [Lownfels & Lewis, 2010: Timber Press] which was based on your research, was, “Nobody has ever fertilized the redwoods.”
Yes! In fact, many of those trees have been there since the time that Jesus walked the planet. How is it those plants continue to be able to take up nutrients? Where do those nutrients come from? If you understand nutrient cycling, you understand that those nutrients are coming from the bedrock, from the sand, silt, clay, rocks and pebbles. The breakdown of that bedrock, every second of every day, means new soil particles are constantly being released from that parent material. If you have the right microbiology present, then your plants will never suffer a nutrient deficiency.
There seems to be a growing awareness of the role these beneficial microorganisms play in the soil. I see them marketed more and more frequently—potting soil preloaded with mycorrhizal fungi spores, organic fertilizer with beneficial bacteria. As a big advocate of compost I’m a little skeptical. Do we have the technology to extract these microorganisms and keep them viable? If so, what do I look for? How do I know if I’m getting the real deal?
Keeping those organisms viable is a problem, especially when you’re dealing with a sealed container. If there were organisms growing in those containers, they would be releasing gases from consuming food and the container would explode. So, we need to put the organisms to sleep. But they don’t have remarkably long-lived dormant stages. About half of the organisms that you would find in compost cannot be put to sleep and they die. You’ve now lost a massive amount of the diversity.
However, 50% is still a lot better than nothing. That’s a good start. But then begin making your own compost, and you’ll get a lot more diversity.
Unfortunately, most of the products in the store that tout things like “microbial inoculant” will contain only bacteria.
Compost extract and compost tea extracts, even if they have been put to sleep, still have a massive diversity of bacteria, fungi and nematodes. If a product says it contains microorganisms, they need to list them, at least the top ones. A good compost extract will have a diversity of bacteria and fungi. If a product lists perhaps only five bacteria, then it’s most likely a waste of money.
One of the best ways to get more “good guys” into your soil is by making and using compost tea. It used to be common practice to add molasses as part of the recipe. I know you aren’t an advocate of that. Could you explain why?
Well, because we already have enough bacteria. Molasses is pretty much strictly a bacteria food, a least in the quantities we use it, and you really don’t need more bacteria. As we’ve been looking at soils over the last 25-30 years, what we see in our modern agricultural method is that we have selected for bacteria and bacteria alone. Stop adding molasses. Your tea doesn’t need that additional food source to grow massive amounts of bacteria. If you add too much, your compost is going to go anaerobic. [This is bad.] I don’t care how fast you are aerating your compost tea, you won’t be able to keep up with the rate of bacterial growth and the oxygen demand that comes with it. You begin to lose your beneficial fungi, protozoa and good guy nematodes, and you might end up actually just growing a bunch of bad guys, pathogens. Sugars in your compost tea are not necessary, and aren’t going to give you the benefits you want.
I live in a desert, as do most of our readers, and we rely on irrigation to keep our plants lush and healthy. My garden beds often dry out if I have nothing planted in them yet. If I have a robust soil biology, can it handle this, or should I try to maintain even moisture in my garden as much as possible, even if that means watering unplanted garden beds?
Most of those organisms are going to be able to find places where they’ll be protected from the drying, and a lot of them will go into their dormant stages. If they don’t have dormant stages they’ll put up a hydrophobic material, to seal themselves in and keep their moisture around themselves. That’s why it can be be really difficult to wet up soil that has been really dry, because loads of microorganisms are hunkered down inside their hydrophobic shells, and water beads off instead of going into the soil.
If you have the proper biology in your soil, they will build the structure so that water will move into the soil and be held there. We have reduced water usage in desert soils this way by as much as 70%, as compared to the conventional agricultural system. If you want to reduce the amount of water you use, then you’ve got to have the organic matter going into your soil to feed the microbes, so that they can build the structure into the soil and hold on to that water. And you don’t want bare soil exposed in these systems, as that is where the water will evaporate from.
Actively Aerated Compost
To give your soil a boost of good microbiology, nothing beats a good batch of aerated compost tea. The liquid needs to be actively aerated, to assure a highly oxygenated environment. As a loose rule of thumb, beneficial microorganisms thrive in an aerobic environment (in the presence of oxygen), while harmful organisms tend to thrive in anaerobic environments (in the absence of oxygen). Anaerobic processes give off toxic gases and smell foul. Aerobic processes smell earthy and good. The process is simple.
Equipment: a five-gallon bucket, a large aquarium air pump (as large, and tubing and airstones for the pump. The airstones are placed in the bottom of the bucket (sometimes you need to weight them), and the pump will push a large amount of air into the liquid, keeping our brew well aerated.
1. In a 5-gallon bucket, add 4 gallons of water. If using chlorinated tap water, run the airstones for 24 hrs to dechlorinate the water. Chlorine is volatile, and blows off easily. This is crucial, as chlorine will kill the microbes in the compost!
2. Add 1 pound of high-quality fresh compost.*
3. Actively aerate the brew for 24 hours, and use within 48. As a soil drench, use full strength. For foliar feeding (spray) applications, strain the mixture well and dilute up to 50% with dechlorinated water, or use full strength. It’s that easy!
Clean equipment immediately, even before using the tea; otherwise quickly forming slime will damage your next batch. Use the tea within four hours. (It will last longer if you continue to bubble air through it.)
Step it up! Feed the microbes by adding 1/2 tablespoon of humic acid and 1/8 cup of kelp (available in garden stores) to the dechlorinated water before adding compost.
* From Teaming With Microbes: If you plan ahead a few days, you can give the compost’s fungal component a head start by adding uncooked oats (fine-ground is best; do not use instant) to your slightly damp compost at a rate of 1 to 4. Place the mixture in a warm dark place, about 80 degrees (use a seed mat if available). After three days, the surface should be covered with long white fungal threads.
A series of online courses featuring Elaine Ingham are available at www.soilfoodweb.com. You’ll find a Life of the Soil course, Composting, and Compost Teas & Extracts, as well as a Microscope Class where you can learn to identify these organisms and analyze your soil and compost.
To dig deeper, join Dr. Ingham for a five-day Soil Food Web intensive at Boulder Mountain Guest Ranch in Boulder, Utah June 29-July 3.
See registration and more information at www.bouldermountainguestranch.com, or call 435-335-7480.