Ash helps gardeners but take precautions

April 29, 2009 

Most garden columnists around the country are answering questions about roses, deer, and moles in the lawn. Not in Alaska. The most frequent question I get these days is about the Redoubt debris and what all the volcanic ash will mean for our lawns and gardens. This isn't the stuff your average garden columnist is qualified to deal with, but I did major in geology in college, so let me take a stab.

On a chemical level, my guess hinges on this year's ash having a similar composition to that of the last decade's eruptions. My geologic training, meager as it is (and my memory worse), suggests this is a safe assumption. That is to say the ash on your lawn (and deck, swing set, garden, wheelbarrow and everything else) is mostly silica quartz with a mixture of calcite, magnetite, gypsum, mica, clay, feldspar and amphibole.

Broken down into English, the elements the ash contains are silicon, calcium, potassium, iron, sodium, titanium, and aluminum. All but the aluminum and titanium are mineral plant nutrients, meaning plants can't live without them. The aluminum can cause problems for plants, but is normally tied up unless the pH of a soil is way out of whack, which shouldn't be the case for Southcentral area gardens. There is so little titanium, I am not concerned about it.

These plant nutrient elements will find their way into the soil solution. That is rain and sprinklers will wash the ash into the soil and the material will start to slowly dissolve. On a molecular level, organic material and clay particles will hold the elements and release them to plant roots. So, if you have lots of organics in your soils, they will retain the Redoubt-given, plant essential mineral nutrients.

The physical aspects of the ash, it is composed of tiny glass fragments, presents both a good and a possibly not so good side to the equation. Once worked into the soil, the microscopic fragments of glass, will help improve soil structure. They will create more pore spaces in the soil because of their irregular shape. More pore spaces means more air movement and water retention. This leads to very healthy populations of microbes working away to care for and feed your plants.

The downside is that the particles can't be that healthy to inhale. I know they irritate the eyes and nose, get into the pores of shoes and dry out the leather. Frankly, who wants to work anywhere near it? The problem is once you rake or sweep, it just flies in the air.

So, the answer to the oft-asked question about the impact of Redoubt ash is simple. The ash will be great for our lawns and flower beds, trees and shrubs. It should greatly enhance the habitat for a healthy soil food web, but it will also provide nutrients to plants.

However, I don't think we should be out there working in the stuff. As of this writing we haven't had any rain, and far be it for me to wish any more moisture from the heavens on Southcentral than we already get. Personally, however, I am going to wait until after we have had a few hard rains before I start moving around mulch and getting the beds and yard in order. Precipitation will wash the ash down.

So, until the dust clears, no mowing, no blowing, no raking and perhaps no sweeping. You should have already given up rototilling, so it won't factor in. Moreover, think about some extra precaution in the form of a dust mask when you are outside working in the yard. Gardening is a hobby. I don't see inhaling bits of silica as having any part to that.


Jeff Lowenfels is a member of the Garden Writers Hall of Fame. You can reach him at teamingwithmicrobes.com or by calling 274-5297 during "The Garden Party" radio show from 10 a.m. to noon Saturdays on KBYR AM-700.

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