The Organic Matter Controversy

Professor Carl Whitcomb of Oklahoma State University created a stir in the Atlanta landscaping community with his statement that organic matter isn't needed to improve the soil in plantings, in fact, it is counter-productive. This was treated as heresy by many, including this author.

Whitcomb's research was prompted by the varying specifications by state Department of Highways. Several state DOTs required contractors to amend the soil with organic matter, using anywhere from 10% to 50%. Whitcomb was curious as to which percentage was most efficient, and therefore, correct.

He experimented by planting nursery stock in 100%, 80%, 60%...down to 0% organic matter in the hole. He used several species and several types of organic matter. He did this in Florida, Oklahoma, and other states. His results were that the 0% organic matter worked best.

This is heresy. Everyone knew that the thing that separated rich topsoil from subsoil is the organic content. How could this be right?

Whitcomb probably wasn't convinced himself, and spent a lot of time on this subject. What he concluded was when the size of soil particles differ between the fine-textured native soil and the coarse-textured organic mix, water is sucked out of the coarse-textured mix and into the fine-textured native soil. This results in drying conditions for the roots.

(This is why I say to water the plants well before planting. It prevents the soil from wicking it out in the early critical days).

Another opinion is that the roots are happy in the rich soil, don't spread into the native soil, and lack long-term performance.

What Whitcomb suggested was to dig great big holes, the wider the better, and skip the organic matter. This loosens the soil for easy root penetration and allows water to soak in. You have one less soil boundary for water wicking. He says wide, not deep, because most roots develop in the upper surface where it can reach oxygen for growth.

Whitcomb also recommended organic mulch like pine straw or nuggets on the plantings. These will break downand add organic matter from the top, just like nature does with fall leaves building up and breaking down. He said to save your money on organic soil conditioner and to invest in mulch.

I was a heretic, but I converted. His data and logic was overwhelming. However, I still add organic matter , and here is why:

He was mostly concerned about individual holes dug for individual plants, where a landscaper digs a 12" hole and drops in a 10" diameter 3-gallon plant. This leads to bad drainage and a lack of root penetration due to compacted native soil.

He said that organic matter was acceptable if you were improving the soil for the area that the roots would fill during it's first five years.

I rarely ever "spot plant" where I dig individual holes. I almost always "bed plant" where I work the soil for an entire bed, providing loose soil for optimum root growth. Therefore, adding organic matter to a bed and tilling it in fits into his "five year root zone" clause, and I can still say I'm a Whitcombian planter.

Paul Burns

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