Instead of amending the soil to match the plant, it’s easier to match the plant to the soil you have.  Native plants like Yarrow (Achillea millefolium) and its many cultivars are well-adapted to the alkaline soils found in dry climates. They thrive in soils with minimal organics.

(photo credit: Okanagan Xeriscape Association)

Kamloops gardeners expect a lot from the plants they choose. To survive in this harsh growing environment, the ideal candidates need to be cold tolerant, heat tolerant, drought tolerant, non-invasive, pollinator friendly and even fire-resistant. Often missing from the list, however, is another important criterion: plants should be able to tolerate the region’s alkaline soil.

What is pH and why does it matter?

Soil pH is important because it affects 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 common.

Alkalinity is measured using the pH scale. The pH scale goes from 1 to 14 where 1 is highly acidic, 14 is highly alkaline and 7 is neutral (having a balance between acidity and alkalinity). Soil in dry climates like ours is generally alkaline. Simple soil pH test kits are available at several local nurseries.

Most crops will survive in a soil pH of 5 – 7.5. When the pH isn’t in the plant’s preferred range, the yield for food crops may be compromised and ornamentals will have fewer flower. Some plants just won’t grow.

According to Bev Herman, a scientist who owns and operates Pacific Soil Analysis, it is harder to lower soil pH than to increase it. Additives like sulfur are a temporary measure.

 “It would likely be a one-year fix. The parent material in the soil will push to return to its original state,” she said.

Finding the right organic soil amendment

Organic matter helps with soil alkalinity and offers many other benefits as well. Organic matter is defined as raw or partially decomposed plant and/or animal residues.

It binds soil particles, granules and aggregates together. It aids water penetration and aeration of plant roots in clayey soils and increases moisture-holding capacity of sandy soils. It also provides some nutrients for plants and food for beneficial soil microorganisms.

Just because a soil amendment is labelled as ‘organic’ doesn’t mean it is worth the cost of applying it. Some organic amendments can actually, lower soil quality.

“Many products can be correctly labelled as organics, for example wood, sawdust, straw, or peat, but they can only improve soil physical properties. They can improve friability, water holding capacity,” said Bev.

These kinds of organic amendments do not decompose to provide many nutrients. Worse, they rob the soil of nutrients that are already present.

Other, “high-quality” organic amendments like animal manures, sea soil, mushroom manures, compost and food waste do provide nutrients as they decompose.

Animal manures are not all equal

Bagged or bulk steer manure often contains excessive salts that accumulate from urine during confinement. Bev stresses the necessity to leach salt from steer manure after being incorporated into the soil

“Several irrigations before planting, or applying in the fall and letting winter moisture do the job are necessary to reduce the sodium level”, she added.

Horse manures can contain weed seeds. This can be a major disadvantage and should be considered before using horse manure in a garden or flower bed. Well-composted horse manure, on the other hand, can be weed-free.

Rabbit, goat, sheep, and llama manures are excellent for use in gardens and can be incorporated without composting prior to planting. Manure from these animals does not contain weeds.

Very few wholesale nurseries include information about the pH preference of a plant on plant tags.  One very useful, credible source of this information can be found at thespruce.com, where plant profiles are reviewed and fact-checked by an editorial committee made up of experienced master gardeners and landscape professionals.