Question: I keep hearing about alkaline soils from Rocky Mountain gardeners but what are they and how do they differ from regular soils? How do I need to garden differently in alkaline soils?
Soils in the Rocky Mountains were created from the weathering and erosion of rocks and mountains. Most mineral matter comes from rocks. Mineral-rich soils have a pH above 7 on a scale of 0 (highly acidic) to 14 (highly alkaline). Soil has a tremendous influence on the availability of nutrients for plants. Because of the structure of alkaline soils, these nutrients and oxygen can be withheld, making it difficult for the plant to take up these nutrients, even if they exist in the soil. This is especially true if the soil is wet clay. Gardening in wet clay is like gardening in a mixture of wet cement and Jell-O.
Where does “alkaline soil” come from?
Take a close look at the image above, which shows Bear Lake, Idaho, where I do the bulk of my gardening. High parent materials of calcium carbonate have given Bear Lake its famous turquoise color but notice the aridness of the mountains in the distance. High pH or alkaline soils are more prevalent in arid climates because there is not enough rainfall to leach the high ratio of minerals from the soils. The precious lake water is fed by high mountain snow that melts in spring and works its way to the lake, washing through layers of rich mineral grains that are part of the shale, sandstone and compacted quartz that compose the mountains surrounding the lake. Tests of the water in Bear Lake are usually in the pH of 8, or highly alkaline. In other words, both the soil and the water in high-mountain valleys everywhere, are highly alkaline.
How do I “fix” alkaline soils?
Trying to change what nature has provided is never really doable, and it is better for the plants and gardens to choose plants that thrive in soil with a high alkaline content. The main rub is that there is no real research or common knowledge on which plants like which soil. I’m not a chemist, I’m a gardener, but I’ve found the following perennials do well in my alkaline soils and water. There are a huge variety, so don’t fret if you happen to live in an area with alkaline soils. Mother Nature has your back and she’s created hundreds of gorgeous perennials specifically suited to this kind of soil!
The mallows like the Malva (the lavender-colored flower shown at the top of the picture) are alkaline-loving perennials as are the Achillea, Antimus, and Leucanthemum. Most Alpine perennials thrive in alkaline soils for they are rock garden plants. Native perennials like the Aquilegia or Columbines shown below are also Alkaline perennials.
Dr. Q, who specializes in gardening in the even more arid climate of Nevada, explains the difference between alkaline and acidic soils in this informative video. While he recommends amending the soil, I recommend an easier method: choose plants that have already adapted to thrive in the soil where you live.
Where can I find alkaline-soil-loving perennials?
Every perennial mentioned in this blog is an alkaline-compatible plant, and so is every perennial profiled in the western regional gardening book, Powerful Perennials. If acid-loving perennials are planted they may survive but will never reach their potential. This could explain why many perennials are shorter and stockier when planted in our Rocky Mountain gardens.
USU extension also has a helpful document for western gardeners who want to understand more about gardening in alkaline soil.