Clay soil, Amending Clay soil, Planting in Clay Soil

In most of the Merced area we have hard-pan clay. Even in some parts of Atwater the sand layer is very thin with the same clay under it. It’s not the end of the world but it takes fixes and tricks to work with it. With organic growing methods natural roles are mimicked as closely as possible by the gardener. Because we like to eat non native plants some adaptations have to be made. I think I should start with what soil ideally could be, then what clay is and how to get your soil closer to ideal.

Soil serves a multitude of purposes directly and indirectly for plants. Its purpose and characteristics change gradually as it gets deeper. I’m going break it down into three layers.

The top 2-3 inches in nature is usually the decomposing plant material from plant litter from previous growth. This zone is where the essential nutrient nitrogen is produced by microbes. This is also the zone that is home to most bugs and their eggs, molds, fungi, bacteria and viruses. Some are detrimental, others beneficial and some essential. We can reduce the detrimental by thoroughly composting this layer away from the plants and then reintroducing it to the soil [See How To Compost]. Roots are rare in this upper layer for most plants. Nutrients from this layer are carried by water to roots below.  Ideally this layer is up to 50% empty space. That space transitions between being filled with air and water. [Future blog about water and air]

The next layer is usually denser. It is the mineral remains and the woodier parts of plants and decomposed rock in some form. It is denser with smaller capillaries, so it has less air and its water holding capability is more than the layer above. That’s why this is the layer we try to saturate when we are watering. This is where most of the roots are. They are gathering nitrogen washed down from above, potassium, phosphorus, and small amounts of a lot of other nutrients from this layer. As gardeners this is the layer we try to make as loose and deep as possible (12 to 18 inches) so the roots can freely spread as far as they wish. This layer has less microbial life and it works much slower due to lower temperatures and less air. In this layer is where earth worms, scarab larvae, the occasional potato bug live. Not many other bugs live down here.

The next layer is even denser. It is compacted from the weight of the soil above. Other than trees, most plant roots have a hard time penetrating it. Most of the spaces between the molecules are filled with water, not much air. It’s pretty dead down here.

 

Now, our clay in Merced is pretty much like that bottom layer all the way up to surface. So, we have to build the top two layers. The reason it is like this is mostly because of the shape of the particles of clay. They are flat, shaped kinda like dishes in a big pile.

It’s really hard to get roots to grow through it and it compacts easily. So we need to break it up. Sand helps a little, but clay and sand is the recipe for brick. It makes it a little more like this.  The clay molecules are much smaller than sand, but I hope you get the idea.

It’s still really hard for roots. So we need to mix in compost until it’s at least 50% compost/sand to 50% clay. That will sufficiently break up the clay and even out its air/water holding capability.

 This only needs to be done once or, anytime the soil becomes compacted. Not walking on the soil will keep it loose. The “mixing in” process [tilling] is very labor intensive. The natural biology of the soil is disrupted by tilling. The micro organisms that live in each layer are moved to a new layer and some die. This is why it is best to till as little as possible and to give the soil as much time as possible to recover before planting.

The top layer is just compost. For most crops like tomatoes and peppers, I add about a ½ inch layer every other week, as soon as the seedlings are a few inches tall. Then slowly increasing to every week until they start to fruit. Then I stop for the season. Leaf crops get it evenly over the whole season.

An edaphologist would probably laugh at this post. Soil science is extremely complex. They usually talk in 4 to 40 horizons of soil. The organisms at work are diverse and numerous.

I can’t bring myself to tell anyone what I think they should do without giving them an equal amount of why I think so. I’ve done my best to explain the “why” in a topic that honestly bores me just before it goes over my head. I hope you find this helpful in dealing with a sticky [soil] situation. clay soil, fix clay soil, amending clay soil, planting in clay soil, gardening in clay, clay, soil, vegetables, vegetables in clay, organic vegetables, soil amendments, compost, composting, making compost, vegetable gardening, organic gardening, Merced clay, Merced gardening