Notes from Growing Vegetables West of the Cascades
Notes from Growing Vegetables West of the Cascades,
6th edition, by Steve Solomon
West of the Cascades millennia of heavy winter rains have leached all of our soils into a kind of chemical imbalance that won’t grow highly nutritious food. Our infertile soils do grow good trees, but they lack succulence, are woody and not digestible by most animals.
Forest soils have two sorts of liabilities. First, the overall amount of plant nutrients has been lowered because most of the minerals our soils started out with (from the weathering of rocks) have, over geologic time, been washed away by rain water passing through them. Second, leaching does not remove all plant nutrients equally. It takes some more readily than others. If all of the minerals had been proportionately lowered, the situation would not be as serious. Unfortunately, the nutrients that allow plants to become highly nutritious---calcium, magnesium, and phosphorus---are the ones most readily lost, causing a significant imbalance.
The essence of our region’s soil imbalance hinges on an overly high level of an otherwise useful mineral, potassium. Our soils usually have lots of potassium,---maybe too much.
What all garden soils in this region need: lime (two kinds) properly balanced organic fertilizer (see his recipe below) and enough organic matter to keep the soil ecology and growing plants healthy.
Our forest soils are acidic, deficient in calcium, and almost certainly deficient in magnesium. Calcium and magnesium are equally important plant nutrients. You’ll come up with about the right proportion of calcium to magnesium by blending together more or less equal parts of calcium carbonate (ground limestone), and dolomitic lime, which is about half calcium carbonate and half magnesium carbonate. Calcium carbonate is sold locally under the misleading name of “agricultural lime” which in the past was the name used for hydrated lime, or calcium hydroxide, which you DON’T want. Both ground limestone and dolomitic lime are inexpensive, especially if you pick them up on sale or order through Gordon in the spring.
A new garden or field will initially need fairly heavy application of both limes, with lighter applications in following years. Solomon gives recommendations which seem a bit high to us. Over-liming can certainly damage soils.
In addition to “trace minerals”, vegetables need five or six minerals (elements) in fairly large quantities: nitrate-nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur.
