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Tue, March 26

Good gardens begin with great soil
And you can make your own soil great by following this advice

Soil is the foundation of life. Nothing sustains life without the foundation of what the soil produces. Our soils either directly or indirectly provide us with meat, milk, eggs, fruits and vegetables, beauty and shade. Whether you are planting fruits and vegetables or annuals and perennials, you need to understand the functioning elements of the soil. It's only called dirt when it's on your car, in your house or all over the kids.

Due to our low rainfall, our soil is alkaline and has little to no organic material. An alkaline soil has a high pH (more than 7.0 on a scale of 0 to 14). The alkalinity of a soil also determines what nutrients a plant can absorb. For example, plants absorb potassium more readily in alkaline soils but have trouble in absorbing manganese. Most garden plants prefer a neutral or slightly acidic soil.

Arizona is dryer and more temperate than most of the rest of the United States, resulting in a gardening experience rarely matched anywhere else. It may be different, but we can still garden here.

Know your soil type

Before starting soil preparation, determine what type of soil you have - sandy, clay, silt or loam - as well as other detrimental growing factors such as caliche and large rocks.

Sandy soils have the largest particles and the least water and nutrient holding capabilities, but allow maximum air circulation. Clay soils have the smallest particles, hold maximum amounts of moisture and nutrients, but allow minimum air flow. Often times they bind up the nutrients which are then not available to the plants.

Silty soils are made from medium size particles. They shed excess water more quickly than clay but not as quickly as sand. Silty soils tend to feel slick to the touch when they are wet.

Part sand, part clay, part silt and the addition of organic matter would be an ideal combination, commonly referred to as loam - a soil that has good water-holding capabilities, maximum nutrient retention and good air circulation. Loamy soils also encourage beneficial microorganisms which reportedly help plants absorb nutrients and resist disease.

Clear out the bad stuff

Large rocks, weed vegetation and caliche should be removed. What is caliche? Caliche is a layer of soil in which the soil particles have been cemented together by lime (calcium carbonate). Caliche is usually found as a light-colored layer in the soil or as white or cream-colored lumps. Layers will vary in thickness from a few inches to several feet, and there may be more than one layer.

What does caliche do to plants? The caliche layer can be so tight that roots cannot penetrate through, restricting root development. Caliche will not allow aeration or water movement, and can lead to salt accumulation and loss of nutrients. These factors will reduce the vigor of the plant and possibly bring it to its demise.

Starting a new gardening bed

If you are not gardening in permanent beds, maybe it's time to start. If you are starting a new bed, pick your location carefully. Consider water availability, wind and sun exposure, and accessibility. Also, identify a possible micro climate. I suggest you start small and allow room for expansion.

There are two ways to start a new gardening bed. One, remove 8 to 12 inches of the existing soil, setting it close by as you will be sifting it and replacing it. Put down a layer of cardboard, any old flattened boxes will do, followed by a layer of newspaper three to five sheets thick and a layer of composted manure about one inch thick.

Sprinkle lightly with ammonium sulfate or urea (both are nitrogen). Sift the removed soil and discard the rocks and debris. Return the sifted soil to the bed, adding 50 percent soil and 50 percent compost. If you do not have compost available, purchase a soil planting mix.

To insure good air circulation and water-holding capacity, add vermiculite according to manufacturer recommendations. The soil, vermiculite and compost or planting mix should be mixed thoroughly, watered until completely moist, and then allowed to set for at least four weeks.

No trespassing

Avoid as much foot traffic as possible on the prepared soil. I personally lay down old boards to use as a walkway. This will reduce soil compaction.

The second method may be a little more expensive, but requires less labor. Select your location and put down a layer of cardboard and a layer of newspaper. Use boards, slump blocks, or anything to make an enclosure about 12 to 18 inches high and no more than three feet wide. Fill the enclosure with 20 percent composted manure, 40 percent compost, 40 percent planting mix (most planting mixes already contain vermiculite) and water thoroughly. Let set for at least two weeks, and you are ready to plant.

Maintaining existing garden beds

For maintaining an existing garden, managing soils to improve tilth and maintain fertilization are related but not always the same process. Compost or manure are added to the soil to improve soil tilth (a physical condition of the soil as related to ease of tillage and suitability to support plant growth) but will add minimum amounts of nutrients. Manufactured or organic fertilizers can be added to supplement soil fertility but will not usually improve soil tilth. Soil amendments refer to any material mixed into the soil.


By law, the term fertilizer refers to a manufactured material that guarantees a minimum percentage of nutrients, at least the minimum percentage of nitrogen, phosphate, and potash. An organic fertilizer is derived from natural sources and guarantees the stated minimum percentage.


Amendments supply nominal amounts of plant nutrients. It is most likely the organic material in a soil amendment is a food source that allows microorganisms to multiply. The larger the number of microorganisms increases the conversion of nutrients already in the soil to plant usable form. In clay-type soils, organic matter (over a period of time) glues the tiny soil particles together into larger aggregates, increasing pore space. This increases soil oxygen levels and improves drainage, which in turn increases root depth, allowing roots to readily reach a larger supply of water and nutrients.

In sandy soils, organic matter holds over 10 times more water and nutrients than sand. Organic matter also encourages the beneficial activity of soil organisms, making nutrients readily available for plants.

In a vegetable garden, the routine addition of organic soil amendments such as compost will optimize potential yields and quality. Your goal should be to increase the organic content of your gardening soil 4 to 5 percent over a long period.

When is best time to start a compost pile? Today!

If you are adding manure to your compost pile, make sure it is aged so the salt has been leached out.

Cultivate all compost or soil amendments into the top six to eight inches of the soil. Do not leave compost in chunks because it will interfere with root growth and water movement.

In a vegetable garden it is not recommended that you add woody materials such as bark or wood chips. They may interfere with seedbed preparation and may result in soil nitrogen depletion.

Repeated application of organic materials builds up a pool of material that releases nutrients very slowly. In the long run, this nutrient supply decreases the need for supplements.

When is the best time to start gardening? Anytime!

Remember, feed the soil, not the plant. If you take care of the soil, the soil will take care of you.


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