Can a garden have too much carbon?
I'm expanding my garden and ran into a former burn pile. I've lived here for a little over 2 years and believe that there was no burning in that spot for at least 4 years (my neighbor remodeled this house). Can my garden grow well under these conditions?
Mesa County Colorado soil and fertility issues
Charcoal is most commonly made from burned wood. It is highly alkaline (high pH) and also rich in potassium salts. Colorado soils are already highly alkaline and rich in potassium. Adding charcoal ashes to gardens here only adds to soil characteristics already in excess, and doesn't supplement deficient elements such as nitrogen that limit plant growth in our area. Supplementing deficient elements is also known as fertilizing.
Increasing alkalinity causes further problems with plants ability to wrest iron and other micronutrients from the soil. The increased salts of a kind not contributing to deficient elements can cause plant salt damage. Further, the fine particle size of ash also tends to plug the pores of clay soils leading to water penetration and drainage problems.
In composting, dry leaves are a far better carbon source to provide energy for composting microorganisms than charcoal ash. Remember that the compost eventually is placed in the garden where the object is to supplement soil deficiencies, not add to excesses.
In short, ash contributes nothing to aid plant growth in our soil types and can only cause plant growing difficulties. Some gardeners may have applied ashes to eastern U.S. soils that are acid and low in potassium. In Colorado, soil circumstances are different and the practice is not recommended.
I suggest you bring us a soil sample from the area and we can do a quick salt test on the soil to make sure it is ok. High alkaline causes vegetables to be less productive and to possible die. We also have soil test kits we can supply to send away for a complete soil analysis.
Our office is located at 2775 Hwy 50 in the fairgrounds. We are open from 8-5.