Part One: Remineralizing Soils––A Winter reading assignment for Pacific Coast Iris Growers

Kathleen Sayce, January 31, 2015

Originally published in Pacific Iris, Spring 2013, and updated Winter 2015

In 2010 I began to learn about providing better nutrition to soils so that plants will grow in optimal conditions. Healthy plants not only overcome herbivory, disease, drought and other adverse conditions to flourish, they grow larger, flower more and set more seeds. These plants have higher levels of secondary plant compounds, sugars, and other metabolites. Optimal nutrition for healthy soils to produce healthy plants is not a matter of applying N-P-K fertilizers; instead the focus is on balancing minerals and adding carbon compounds.

Systematically testing soils is the first step; the second step is adding those minerals that are low or absent from your soil. Adding additional organic matter, or carbon, in the form of compost, fungi-inoculated wood chips and biochar is another good step for some soils, particularly temperate forest soils. Plus patience, and resampling soils every year as you change the mineral composition. I was excited to see how my plants would respond, even though I grow few food plants (some herbs, a few parsley plants––all plants that deer usually avoid).

In my garden, historically I used compost and biochar every time I planted a new iris. Every two or three years, a new layer of compost was added over each garden area. I've also used wood chips, preferably red alder chips, aged for a year so that fungi have inoculated them before they go into the garden beds. I've done this for more than 20 years, and until 2010, I thought I was doing pretty well. That year I began reading about minerals, soil carbon, and soil health.

First, I read the latest book from Steve Solomon on vegetable gardening, The Intelligent Gardener. Steve lives and gardens in Tasmania; in a former life he lived in Oregon, where he started Territorial Seeds, a vegetable seed company for the Pacific Northwest. He and his family lived on what he could grow in the garden for several years. He composted, irrigated, added manures, and generally followed traditional organic farming guidelines. It took him decades to learn about how to make high quality composts, and even longer to learn about soil minerals and soil health. Now in his 70s, Steve's latest book is a tour de force for gardeners, distilling a lifetime of gardening knowledge for all of us. Whether you garden for pleasure, or food, or both, read this book.

Second, I read Michael Astera's book on soil nutrition and cation-base exchanges, The Ideal Soil: A handbook for the new agriculture. IMO, a gardener with high school chemistry will understand both Solomon's and Astera's books. 

For a third read on this subject, there is Jeff Lowenfel's Teaming with Minerals, a companion to Teaming with Microbes. Read both of them too.

Jeff Lowenfel's books on soil health are
great reading for gardeners. 

Living in a high rainfall area, it makes sense to me that water soluble nutrients are low in my soil; the opportunities for them to mobilize are too good. Yet compost and well-inoculated wood chips are not be putting back everything that my soil needs in the way of minerals. In fact, water soluble nutrients probably wave at plant roots as they wash past during the wet season. Hi! Good-bye! And they are gone.

In 2012 I took a bold step forward, and sampled my soil. The samples were sent to a soil testing lab. A bold step for me, that is; thousands of farmers and gardeners do this every year. The report came back, full of numbers, a few were high, most were low. The conclusion was that my soil had three minerals in sufficient or excessive amounts (Iron, Zinc and Magnesium). All other elements were nonexistent or at very low levels.

The facts:  too much Mg, Fe and Zn, not enough Ca, and some minerals were incredibly low.

I measured the area of all my garden beds, and took the soil sample results plus the area measurement to a local soil consultant to have a custom blend of minerals formulated for my garden. The soil consultant avoided Calcium compounds that might change the pH of my naturally acidic soil or add more Magnesium. 

My soil consultant did the calculations by hand, but there are websites where you can plug in your numbers and have the needed amounts of minerals calculated for you. For example, http://growabundant.com has an online calculator. 

We settled on a formulation that would build up minerals over several years, not trying to bring this garden to an optimal mineral level in one year, but rather to bring it up more gently over three to five years. It was a cautious first step, in hindsight. I went home with three bags, to apply in midwinter, late winter and early spring.

To learn what happened, see Part Two later this week.