Soils of Norman, Cleveland County, Oklahoma

Bonus content for How to save the world with plants #04 by @cast-iron-garden.bsky.social

This page is a work in progress!

Soil basics

Usually when you see soils described for a given plant in gardening, they talk about drainage; moisture (dry to wet); particle size as sand, loam, or clay (caliche is also listed on Native American Seed’s website, but I haven’t seen it in our area); and nutrients. Most gardening pages don’t mention the soil horizons but it’s vaguely helpful and also pretty cool, so I’m including it at the end. (Those are the layers as you go deeper into the ground.)

Drainage and moisture

different soil types also hold different amounts of moisture longer or shorter time periods, but that can also be affected by the location of the site (a hilltop versus a valley between higher spots). So these are related but slightly different. You can have moist, well-drained soil, but you can also have moist, waterlogged soil (more of a swamp). Plants need air to their roots so their adaptations to this condition matters for growing.

Particle sizes (also called soil texture)

This section will contain links to various extension service home test pages on how to use a jar and water to sort out particle sizes. I found a few different variations. - MSU Extension Service - USDA Soil Texture Calculator - CSU Extension Service - GrowIt BuiltIt blog’s example pictures

To me, the commonalities are - You have to mix the soil well and it needs to not be too clumpy. Sieving (which I failed to do, being unmotivated) and dish soap seem to be the two commonalities here. - You have to give the clay particles (the smallest ones) time to settle. That can be anywhere from 24 hours to weeks. - The time given for viewing and marking sand particles is between two minutes and an hour. - The time given for viewing and marking silt particles (the next size up) is between two and 24 hours (?) and they can settle to compress eventually. Measure after compression? - The color of the particles does not matter. You’re looking at size. I noticed in mine that the sand layer had a mix of dark to light particles, and again in the loam layer. Particle size is continuous, of course, so using the time windows given above are helpful but not exact.

Nutrients

Loam is just a mix of particle sizes, though we tend to associate it with river bottoms and soil with a lot of nutrients. But, it doesn’t have to have a lot of nutrients. The particle sizes would still be there even if you slurped all the nutrients right now (like potato farming? find reference). Too much nutrient supplementation is not helpful (and can be difficult or unhealthy) for many native plants in their natural habitats.

Soil horizons (the layers)

The cool SoilWeb Map that lets you look at the layers at any given address in the United States.

If you live in a new housing addition (or are restoring a hard-used agricultural land), sometimes you will be missing one or more top layers that tend to contain nutrients and microbial partners. You may need to start with really tough colonizing plants or supplement with compost or microbes to get a jump start on a later-succession ecosystem.

Because most prairie plants will have deep roots, you can look at several layers in your soil profile to see if there’s anything dramatic to limit your species. Usually sand specialists requiring well-drained are less common. I had a hard time finding anything that’s really a clay specialist, because everything but the sand specialists can deal with it.

General types according to gardening reasons with some characteristic species

Ecological site descriptions from USDA. I tend to use indicator plants as well (need to read article). vegetation types are correlated with soil types, and closer to what you might need for gardening though not exactly.

Sandy loam

This is most of Norman, especially central and south. I will place two pictures from my yard.

Brown and red sandy clays

It only takes a small percentage of clay-sized particles to make a soil feel sticky and have big cracks in the dry summer. This soil is common in a lot of central and north Norman. Most native species are fine with it. Even with the clay, spots with elevation don’t hold water and are thus still well-drained. I’ve only heard of this being a problem for house foundations, picky non-native species, and domestic vegetables (especially root vegetables).

River “sand” and loam

The closer you get to the Canadian river and creeks, the more well-drained loose soil types you tend to get. There are also occasional ancient sand dunes (such as in Oliver’s Woods Preserve by Highway 9 on the south end of town) at a smaller scale where you can detect differences in growing conditions. For example, in my own yard, the north side of the driveway has more sandy and more trouble keeping any grass (and more sand-burs).

Eastern red sandstone

This is where the Cross Timbers post oak and blackjack oak forests naturally grow. You start to see these rock formations as you go east and northeast of town, such as around Lake Stanley Draper (technically Oklahoma City) and Lake Thunderbird.