Building Healthy Organic Garden Soil
Bringing abused soil back to life
The soil in California, especially in Ventura County, tends to be very rich. We have so little water that the mineral content is generally high, with the exception of nitrogen. This is true of the Antonio Garden soil, a rich sandy loam with great potential, but in suspended animation.
Nitrogen, in all its forms, is extremely soluble and washes away with excessive watering, even as little rain as we get. We will need to add nutrients, such as compost that should be worked into the whole garden within a few weeks, and through growing ‘cover crops’ and ligumes (beans, peas, etc.).
These cover crops are hardy, have strong root systems, and in cooperation with the micorrhyzal bacteria which form a symbiotic relationship with the roots, helps fix gaseous nitrogen from the air and store it as usable nitrates in the soil.
Some soils will show a lack of available minerals when the soil is alkaline (which ours is). If the pH is adjusted, even slightly, towards neutral, all the trace elements should magically appear and be available to your plants.
Healthy soils are loose, with a porous structure, containing some organic material to feed the soil residents, plus air and water. This ‘life’ consists of earth worms, various and sundry, increasing smaller, animal, fungus, and bacteria. These are not bad, but necessary mechanisms for breaking wood and similar organinc material into the basic forms that plants require.
Although some fungi and bacteria and plant pathogens, the over-whelming balance of prey and predators keeps a natural balance. Some of the bacteria we want to develop in a healthy soil feed on both the cellulose in wood products, but also on pathogenic root-rot fungi (which also have cellulose cell walls).
Most of this life, and the majority of plant root systems, is within the top 12″ of soil, 18″ for larger shrubs, and as deep as a few feet for trees.
Luckily, this is a region where we can amend the soil to help it re-achieve balance and vibrant life. A good (and humorous) look at what makes up healthy soil can be found one the ‘Garden Wise Guys’ web site. The episode is called ‘Journey to the Center of the Dirt’).
The easiest way to open up the compacted soil is to spade, fork, or roto-till in compost or soil amendments. With the county’s mandatory green-waste recycling ordinance, compost (low-grade and sometimes of questionable nature) is locally available at the cost of hauling. Agromin has been generous in their suppport of our garden. Nursery products to consider include redwood sawdust or shavings.
The redwood products are generally marked as ‘treated’ or ‘nitro-lized’ to show that nitrogen fertilizer has been added to them to make up for the nitrogen that will be used by bacteria decomposing the material. Compost has adequate nitrogen already in its make-up.
Many of the plants we grow are ‘nitrogen-fixing’. This means they coexist with microscopic bacteria, and together they sequester nitrogen in the soil in a form plants can use. This is extra nice since nitrogen is both heavily used up and it is also very soluble, meaning it will readily wash away…
A note on roto-tilling: Although it is the easiest (physically) way to incorporate organic material into the soil, pulverizing the soil into a fine powder should be avoided. Soil has a natural structure, specific to its make up, that develops over time. Soil will recover from roto-tilling, but it takes some time to do so.
My preferred soil prep method is to add a layer of amendment to the top of the rough graded soil, work it in with a garden fork, lifting blocks of soil and letting the amendment filter between the blocks as I move down the rows.
When the soil is finally graded, it is not necessary to break the soil into fine particles to rake out – we are going to cover the roughened surface with mulch and it need not be pool-table smooth. Some texture to the surface will help retain moisture that might otherwise run off.
Once we open up a compacted soil, and both air and water can penetrate, and the hard, compacted dirt comes back to life. Finding that worms have moved back into your garden is a very good sign that life is returning.
The various creatures ‘churn’ the soil for you, slowly but surely. Nutrients are consumed at the surface, and the creatures digest and deposit the remains throughout the soil’s life zone.
A 4″ thick layer of mulch can added to the top of the soil to insulate the soil from heat (which kills or supresses the soil organisms), from the drying winds (which evaporate water and deposit salts at the soil’s surface), and also provide a source of nutrition for the soil organisms. When they die, these roots leave channels for air and water, and soil organisms start to break them down in place.
The more you grow in your soil, the more you grow your soil.
Go to the next topic: Vegetable Gardening Tips