by High Country Gardens
The Importance of Soil Drainage in Your Garden
Soil drainage is a very important factor to consider when planting Salvia, Agastache, Lavender, Penstemon and other perennials that like "well-drained" soil. The essential element in well drained soil is oxygen, which is just as important as water in growing healthy plants. Soil that is water-logged does not drain well and is anaerobic (oxygen deficient) resulting in drowned and rotted roots.
In addition to enabling more oxygen to get to plant roots, there is another great benefit to improving drainage: it takes more heat to warm up water than it does to warm up soil, so you can count on an earlier start to your planting season if your soil isn't water-logged.
Identifying Native Soil Types
How you create "well-draining soil" is dependent upon the makeup of the soil currently in your garden.
Sandy soils will drain easily—perhaps too easily. In addition, sandy soils are notoriously bad at holding nutrients, requiring more fertilization. Amending the soil with organic matter will help on both counts.
Clay soils often hold too much moisture, squeezing out the oxygen between soil particles and producing a dense texture that is difficult for roots to penetrate. Compounding that problem, clay soils can crack at the surface when dry, creating fissures which expose roots to sun and arid heat. And as it dries, clay uses reverse osmosis to pull water OUT of the roots of plants in order to maintain its moisture level. Sticky and heavy when wet, hard as a rock when dry—if you have clay soil and wish to preserve your tools and sanity, amendments or raised beds are a must.
Caliche is a combination of calcium carbonate and clay. This combination forms a layer of very poorly draining white chalky alkaline clay. A caliche layer will typically occur from 6 to 12 inches below the surface soil layer. Dealing with it isn't easy—often requiring a pickax and a ferocious battle of wills. When planting deeply rooted trees and shrubs be sure to "punch through" the caliche layer to the soil below. This will greatly facilitate drainage through the hardpan.
Enriching and Improving Native soils:
To improve the fertility and water holding capacity of sandy soils dig in compost. Compost can also be added to improve air penetration and drainage in clay soil. Include Yum Yum Mix fertilizer, Planters II trace minerals and phosphate at recommended rates and dig the compost into the native soil.
Note: Avoid too much compost; use amendments in a 1/3 compost to 2/3 garden soil ratio. Also keep in mind that even bagged "topsoil" should be mixed into the existing soil and not used by itself.
Creating "Well Drained" Soil in Clay
The essential element in well drained soil is oxygen. When planting perennial plants that like well-drained soils in clay, the best thing to do is to create a raised bed or berm (mounded pile of soil). Mix the native clay half and half with coarse sand or crusher fines. (DON'T use fine sand; this will create concrete.)
If planting hardy garden perennials you should add compost and Yum Yum Mix to the soil (1/3 to 2/3 ratio) before mixing the soil with the sand. Mix the sand and enriched soil as you are filling the raised bed or piling the berm.
For plantings that include Penstemon, Salvia and other xeric native plants, mix only sand and clay leaving out the compost. Compost and Yum Yum Mix are mixed by the handful into the individual planting holes to avoid an overly enriched soil mix.
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