The Arizona Soil pH Challenge and How to Deal with it

The Arizona Soil pH Challenge and How to Deal with it
We are living on a limestone mountain and so Iron deficiency and alkaline pH are things we live with here. Like many other plants, Grapes are susceptible to chlorosis, and symptoms of iron deficiency tend to be common on soils rich in limestone.
When I moved here from Michigan, many long years ago, being an avid gardener, one of the first things I did was improve my garden soil. I went to the garden supply store and ask for a bag of limestone for my garden. The clerk laughed and ask “Where are you from? Another transplanted Eastern gardener, right?” “Honey, you don’t need limestone, you’re living on a limestone mountain now!! Those acid soils back east need limestone, we need the opposite here. Ironite and Sulphur help our alkaline soil, but good old-fashioned compost and manure will really make gardening easier.”
If soils are too acid or too alkaline it ties up the nutrients in the soil and makes them unavailable to plants. So you pile on the fertilizer and your plants are still not happy. Here’s where compost and manure come in. The micro-nutrients in compost contain living micro-organisms that improve the soil and neutralize the pH so that nutrients are available to plants.

Arizona soils present many challenges to gardeners and landscapers unfamiliar with the area. It is important to realize some of these challenges so that we can spend our time efficiently and be productive in trying to improve them. Soil alkalinity, or rather the effects of it on plants, vexes landscapers and home gardeners alike.

Alkalinity is measured using the pH scale. You can skip this paragraph if you understand pH, or just want to know that neutral is good and really don’t need to know why. The pH scale goes from 1 to 14 where 1 is highly acidic, 14 is highly alkaline or basic and 7 is neutral (having a balance between acidity and alkalinity). The abbreviation “pH” stands for “potential of hydrogen” and refers to the amount of hydrogen ions in a solution. The pH scale is not linear but logarithmic. That is, a soil with a pH of 8.5 is ten times more alkaline than a soil with a pH of 7.5 and a soil with a pH of 6.5 is a hundred times more acid than a soil with a pH of 8.5.

To give some points of reference using common liquids, lemon juice has a pH of 2, vinegar is 3, milk is 7, baking soda and sea water are 8.5, milk of magnesia is 10.5, ammonia is 12, and lye is 13.

The pH of soil refers to the way the saturated soil solution interacts with other soil compounds and nutrients. A near-neutral or slightly acidic soil is generally considered ideal for most plants. With some notable exceptions, a soil pH of 6.0 to 7.0 requires no special cultural practices to improve plant growth. Most soils in Arizona are alkaline and have a pH of between 7 and 8.5. Native plants are adapted to these conditions. However, introduced landscape and garden plants often struggle as the pH approaches 8.5.

Soil pH is most critical with respect to nutrient availability. Nutrients such as iron and zinc tend to become less available to many plants in alkaline soils. In our area, iron deficiency is most common.

Symptoms of iron deficiency are chlorosis (green veins with yellow or whitish areas in between) on the new growth. Older leaves remain green. These symptoms are especially prevalent on Photinia fraseri plants when they break bud in spring.
Iron deficiency is most common in the spring when daytime temperatures climb, but soil temperatures remain cool. Additions of soil sulfur can help acidify soils to overcome these deficiencies, but it is very difficult to apply enough to make a significant difference, especially over the long term. Soil sulfur should be applied to alkaline soils where annual crops are grown. This can be repeated each season.
The fastest way to overcome iron deficiency is to apply chelated (pronounced kee-lated) iron to the foliage. Chelated iron products have been prepared in a specific way to keep them readily available for absorption once they are introduced into the soil. The chelation process prevents them from being rendered unavailable by alkaline compounds in soil. Some gardeners use Ironite applied to the soil to overcome iron deficiency. This is usually ineffective, because Ironite cannot release enough iron to overcome an iron deficiency.
Zinc deficiency is most common on deciduous fruit and nut trees. Zinc deficiency is characterized by small leaves that are curved, have wavy edges,

have dark veins and yellowish blades, or leaves only in small bunches at the ends of the branches. To correct this, apply a zinc sulfate solution to the foliage when leaves first emerge, and two or more times until all new leaves have developed. The zinc sulfate only affects the young leaves it contacts. As the leaves mature, the thickened leaf cuticle will prevent the zinc from entering.

Once understood, we can make alkaline soils more productive by applying the appropriate nutrients, building raised beds, or planting less susceptible drought adapted landscape species.

Some plants don’t seem to mind, or actually like a little alkalinity, or poor soil. When I have plants, I’ll let you know if they are adapted to our soil, or if it’s important to provide them with amended soil in order to be happy.
Fortunately, you can test your garden soil pH without a soil test kit for a fraction of the price. Collect 1 cup of soil from different parts of your garden and put 2 spoonfuls into separate containers. Add 1/2 cup of white vinegar to the soil. If it fizzes, you have alkaline soil, with a pH between 7 and 8.
If it doesn’t fizz after doing the vinegar test, then add distilled water to the other container until 2 teaspoons of soil are muddy. Add 1/2 cup baking soda. If it fizzes you have acidic soil, most likely with a pH between 5 and 6.
If your soil doesn’t react at all it is neutral with a pH of 7 and you are very lucky!
Acidic amendments that make alkaline soil happy.
Hardwood leaves, like maple and oak, chopped up is better.
Pine needles are great, and they don’t blow away.
Peat Moss from the garden department is a good way to add acid.
Coffee grounds mixed in the soil around plants.
Organic soil acidifiers like Garden Suphur, Dr Earth, Acid Lover’s Fertilizer and Organic Acid Acidifier.
Hope this helps your understanding of soil pH and happy gardening.

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