Amending our Soils
The traditional way to amend soils is to add organic matter because organic matter helps sandy soils to retain water and soluble nutrients while helping clay soils to form clumps leaving space for air and roots. It sounds like the ideal solution but as might be expected, nothing is quite that simple.
One of the problems with organic amendments is that they don't last long. They break down especially rapidly in our alkaline desert clay soils then we're right back where we began. It's not so bad in beds of annuals where the soil can be turned under every year and more amendments added, but that doesn't help with trees and bushes that could live for decades or even centuries.
Another problem with using organic amendments when planting trees, especially in our hard dry clay, is that we tend to create what amounts to a large pot. The roots of the growing tree spread out quickly through the amended soil up to the edge of the original hole where they suddenly encounter the wall of our pot, they turn, and they grow around in a circle. What often happens is that the soil in the artificial pot becomes saturated with water and soft during the monsoon and the roots have nothing solid to grab. Making matters worse, the amended soil allows the tree to grow tall and top heavy so that a strong wind easily topples the young tree which had seemed to be growing so very well.
Over thousands of generations, plants with characteristics that increase their chances of survival in our harsh environment survived and reproduced causing adaptations. One common adaptation is slow growth. When we add organic amendments to the soil, these plants may grow too rapidly with long thin trunks and stems and may die early.
Some plants have increased their chances of survival during periods of dehydration by producing flowers abundantly to initiate a heavy cycle of reproduction. When we add amendments to the soil to prevent dehydration, the result is a reduction in flowering.
| "When we amend our dry hard clay soils with organic matter then plant flora that's adapted to the harsh environment, we're fighting nature and while the plants may appear to be thriving at first, they will often do better long term in a more natural environment." |
When we use organic matter then plant flora that's adapted to the harsh environment, we're fighting nature and while the plants may appear to be thriving at first, they will often do better long term in a more natural environment. Using a mesquite tree as an example, experts recommend refilling the planting hole with the same unamended soil that was removed without adding any amendments. Otherwise, the tree could become top heavy with roots growing in a circle instead of spreading out as an anchor. In high winds, such a tree could easily blow over.
Plants that are adapted to dry environments may also be poorly adapted to moist environments. Adding organic materials can improve the ability of our soils to retain water so much that the plants drown.
Another way to amend heavy clay soil is to add sand. The problem is that because a little clay goes a very long way, an enormous amount of sand must be added to change the overal character of the soil. What must be done would be to essentially replace the native soil with sand which is usually prohibitively expensive and requires removing the native flora. Nevertheless, this can be the only practical solution if you want to grow a small patch of lawn or a flower bed in an area like my back yard which is almost 100% clay.
I've just been reading about using cross-linked polyacrylamide as a soil amendment. This inorganic substance absorbs water and swells up, allows plant roots to take the water, and shrinks as it loses water leaving air pockets in the soil. For sandy soils, it increases the capacity to retain water and soluble nutrients because it can hold up to 400 times its own weight in water. Like organic materials, it doesn't last forever but it can last many years. Each cubic yard of soil takes about two pounds of cross-linked polyacrylamide.
As mentioned before, the easiest option is probably to just select plants that have adapted well to this soil. But if you really want to grow some plants that don't like our soil, and chance are good that you do, raised beds and planters make a good option. They can be built with railroad ties, cement blocks, concrete stacking blocks, rocks, cattle watering troughs, a large satellite dish, hypertufa (lightweight artificial stone) planters, or anything that you can buy or recycle that will do the job. I bought some plastic barrel halves used for watering horses, drilled drainage holes in the bottom with a hole saw, and covered the holes with galvanized hardware cloth to keep out the critters. Using potting soil and watering with drip irrigation, they've worked fine for tomatoes and now I'm trying other veggies.
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Watersorb — "Watersorb home of fine quality super absorbent polymers and water crystals." Supplier of cross-linked polyacrylamide.