I must extend an apology. As a boy gardening at our home in Lisbon, N.D., and on my grandparent’s farm between Alice and Fingal, I naively thought all soil was probably similar to ours, which was a pleasant and workable soil.
However, I would read longtime Forum newspaper columnist Dorothy Collins bemoaning the heavy clay soil of the Red River Valley in her garden column that I enjoyed every week. I wondered if Fargo and other Red River Valley gardeners were just being picky about their soil.
Now I offer a heartfelt apology for my past thoughts, as I’ve gardened in the Red River Valley soil for the last 40 years. Yes, it’s a rich soil, but the word gumbo is descriptive and I realize past gardeners were not simply whining.
The gooey clay soil is slimy when wet and bakes to concrete when dry, with cracks wide enough to lose a good-sized wrench if you happen to drop one.
Clay soils have an upside. They retain moisture during dry periods, and tend to hold nutrients longer than sandy soils through which water and fertilizer quickly percolate downward.
But clay soil is definitely difficult. What can we do to improve a heavy clay soil, whether it’s in the Red River Valley, or other heavy soil around the region?
A common question is whether the addition of sand would improve the workability, texture and drainage. Oregon State University says, "No amount of sand can be added to a clay soil to change its texture. The large sand particles provide a surface onto which the tiny clay particles adhere. The result can be a more difficult soil to manage than the original clay.”
That makes sense, because you can make bricks from clay mixed with sand. They key to improving clay soil is organic matter, including compost, manure, leaves, straw, untreated grass clippings and peat moss.
Oregon State University continues: “In finely textured clay soils, organic material creates aggregates of the soil particles, improving drainage and making it easier to work. Soil with good tilth does not come about with a single addition of organic material, but from a consistent soil-building program. Repeated additions of organic matter change the physical properties of clay soils, but these additions must be regular in order to maintain the changes. There's no break for people who garden in clay."
How much organic material should we add? Three inches of organics added to the soil surface of gardens and flower beds each year is a good rule of thumb. Fall is an effective time to add a generous layer of leaves, bagged manure, compost or peat moss to the soil surface and dig or rototill into the top 6 inches of soil. By next spring, you won’t recognize leaves or whatever material you’ve added, as it decomposes rapidly into rich substances.
Organic material doesn’t even need to be incorporated into the soil for its beneficial effect. In flower gardens and between rows of vegetables, organic material can be applied as a surface mulch, which reduces compaction, encourages soil microbes and improves the topsoil as it decomposes on the surface.
Limiting tillage is linked to better management of heavy soil also, as reduced tillage increases soil organic matter, soil carbon, nitrogen and the all-important soil microbes that keep soil healthy.
Clay soils aren’t the only types with challenges. Sandy soils can be difficult because they don’t store water readily and can’t provide the consistent moisture most plants need for healthy growth, and they don’t store nutrients well.
To improve sandy soils, spread 3 or 4 inches of organic material over the surface of gardens and till into the soil before planting. Do this initially when preparing gardens and keep plantings well mulched. As mulches break down, they continue to add organic matter to the soil.
Don Kinzler, a lifelong gardener, is the horticulturist with North Dakota State University Extension for Cass County. Readers can reach him at firstname.lastname@example.org or call 701-241-5707.