Master Gardener Monthly: Gardening in Arizona Soils

Picardo_Oct_03

Rick Coggins PictureBy Ric Coggins

According to the Arizona Master Gardener Manual, “The ideal vegetable garden soil is deep, friable, well-drained, and has high organic matter content.” “Friable” is a term that refers to the soil’s ability to be readily crumbled into smaller fragments. Most soils native to Arizona tend to be shallow, mostly clay in structure (the opposite of friable) and are usually lacking in any organic matter. While there are some varieties of garden plants that tolerate clay soils, many of the plants we wish to grow struggle in this soil environment.

Soil pH is also a factor in plant roots’ ability to absorb nutrients. The optimum pH range for most plants is slightly acid to a pH neutral, between 5.5 and 7.0. Most central and southwest Arizona soils will range around 7.5 to 8.0 pH or higher. Our alkaline pH soil can inhibit a plant’s ability to absorb nutrients as phosphorus, magnesium, manganese, boron and zinc, even if these are amply present in the soil. These issues require a certain degree of management if vegetables, fruits and ornamentals are to be successfully grown in our region. A soil test can be performed by a reputable test lab that will tell you exactly what you are beginning with and make certain recommendations on the steps needed to amend your soil.

Soil Amendments

Soil amendments are substances we add to the soil to improve its quality. Amendments can be natural or synthetic. Fertilizer is a great example of a soil amendment. While scientific research indicates the individual plant responds no differently to a natural amendment over a synthetic amendment, other research shows that the overall biological health of the soil improves best with natural amendments.

As previously mentioned, most Arizona soils lack organic matter. With an ideal organic content of five percent, we usually find our soils to contain less than one percent. Amending your soil with composted organic material is likely the single best thing you can do for your garden. Composting your household and workplace organic matter is a good way to gain “free” soil amendments.

Soil amendments are not a one-time “fix.” Rather, they are a long-term solution, which over time will improve soil drainage, texture, and will increase the soil’s bioactivity

Raised Beds and Container Gardening

Raised bed and container gardening offer an effective alternative to amending your “in ground” garden soil. Like ponds and aquariums, raised beds and container gardens are basically “artificial environments” which provide the necessary habitat for its desired resident’s survival. Confined, elevated spaces can be filled with soil and organic composition perfectly matched to the needs of your desired plants. This way, you can begin with soils that would otherwise take years to build in the ground.

The framing materials for your raised beds can be wood, concrete, recycled materials, metal or anything that is strong enough to support and confine your “soil islands.”

Once the walls are constructed to your needs, they are filled with soil. Beginning with a coarser base of gravel will afford good drainage, especially for plant varieties that don’t like “wet feet.” The remainder can then be filled with a mixture of native soil, composted organic material and a little sand for good measure.

Raised bed and container gardens are easy to manage in terms of fertilization and irrigation. It’s also easy to create cloches (covers) that will allow shade from the summer sun and protection from winter frost. Of course with container gardens you can simply pick your plants up and move them indoors or elsewhere should the weather become too cold or too hot.

March Planting Guide

March is a busy month for our spring and summer gardens. We are still able to plant artichokes, and it is also time to plant basil, either from seed or transplants. By mid month you can plant lima, snap and yardlong beans. You are safe to plant beets as long as you get them in by March 15. Now is the time to plant most of your sweet corn and cucumbers from seed. March is also the month to set out your eggplant transplants. You would also do well this month in planting your cantaloupe and watermelon seeds. Tomato and pepper transplants, sweet potatoes and pumpkins, as well as summer and winter squashes should also be planted in March.


For more on soils, raised beds or what to plant in March, ask a Master Gardener! Call the “Plant Help Desk” at (602) 827-8201 or email maricopacountyplanthotline@gmail.com.

Ric Coggins is a University of Arizona Master Gardener (Maricopa County) who grew up on a one-acre garden tended to by his father, who was a regular contributor to organic gardening and farming magazines. Ric continues his father’s “green” traditions, owning and operating The Fool on the Hill Farm, a one-acre organic garden homestead in Mesa.

Read more about gardening at greenlivingaz.com/greenthumb

1 Comment
  1. I really enjoyed reading your article. I have been interested in learning about how to grow plants in Arizona for a long time since I seem to have a “brown thumb”. All of my previous farming endeavors have been sadly unsuccessful, and now I know why. Thank you so much for your informative publication, I look forward to future articles.

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