• The Collected Seed

Clay soil. My biggest garden challenge.

Every good garden starts with good soil. This means that if your soil sits on the extreme end of any of the soil spectrums, whether its the soil type (eg: sandy, rocky, clay, etc), or factors such as being badly degraded, contaminated, or having an inordinate pH (acidic or alkaline), finding balance will take work. Gratefully, it pays off in the end with healthier plants and more vitamin rich produce.


Preparing for my mason jar soil test. More about that below.

My challenge is heavy clay. I wish I was joking about this but near my house, this heavy clay soil is actually used to create bricks. I believe soil texture is like the weather, no one is ever happy with theirs, but there are extremes and I'm living on top of one.


Knowing how to deal with soil extremes begins by knowing what you're dealing with, and that starts with having a history of the property. In my area, former pastureland is being quickly converted into neighborhoods which could mean badly degraded soil and even soil contamination from years of single crop farming. If that's the case and you know you want to garden, get a soil test. A county extension office can help with that. In some of the urban neighborhoods, lead contamination is a problem because of pesticide and termite treatments that are no longer used but have left behind contaminates that will stay in the soil for decades or longer. This is again something history and a soil evaluation could reveal.


Looks can be deceiving. The middle arrow in this photo (right side) appears to point to sand, but that would be on the bottom. The very bottom in this case is silt. The light band is a light colored clay (middle arrow) and the top arrow points to where the clay and water separate. This indicates I have a very heavy clay with a little silt but not enough to be considered a clay silt.

I knew my house was set on heavy clay when I moved in and for that reason from began gardening here with my first large (6'x3'x3') container for growing tomatoes. I didn't understand the extent of my "heavy clay" until I did my first Mason Jar Soil test, a technique I learned in a gardening book given to me by my husband's aunt. It's no longer in print but this explanation from Gardner's Supply Company is a good summary and the soil triangle is the best.


By dissolving your soil in a jar of water, you're able to evaluate the ratios of clay, sand, silt and organic matter. As these settle, they should form bands in the jar, allowing you to estimate what percentage of each is in the soil. During my first test, I kept waiting for bands to form and never saw any. I had only clay settling to the bottom. When I repeated the test for this post, some bands appeared but still, it revealed heavy clay soil with just a little silt content..


I was already a composter but I knew the problem was bigger than my bit of hobby composting would be able to address. I also considered that long term, I wanted much more extensive gardens than containers could provide, and purchased soil would be cost prohibitive, so I dug into my soil health education. I've learned about and tried many methods to improve my soil and increase organic matter, and I'll discuss those in future posts. The first step to winning any battle though is to understand the opponent. Here's what I've learned in 5 years of dealing with my heavy clay.



Understanding clay soil


Clay soil is the exact opposite of sand, it has very fine particles and holds water a little too well in many cases. It doesn't absorb water very well though, which I imagine is one of the many curve balls Mother Nature throws at us just so she can sit back and laugh. While sand and clay are opposites. adding sand to clay is a NOT a solution. That's a bit like adding gravel to concrete mix - it makes it stronger.


Clay soil becomes mortar-like, contracting tightly when dry which creates several problems. It cracks badly, with cracks in my yard sometimes measuring a half inch across and a few inches deep. This can become serious enough to cause building foundations to crack from instability as it pulls away from structures. These tough as concrete characteristics make dry, hard clay soil impenetrable by plant roots and makes for back breaking work for the gardener. It's not any easier to work with when wet because it is literally heavy and sticks to every tool. Imagine digging your way through a tub of modeling clay and you'll have an idea of what it's like to work in my yard when the soil is saturated. Wet clay causes further damage to plants and the soil profile through compaction. It's important to just stay off of clay soil when it's wet, something I realize is easier said than done. This is also the slowest draining soil-type, something important to realize when choosing plants.


It's not all bad news though when it comes to clay soil. In addition to holding water, clay soil also holds on to minerals and is usually very rich in micro and macro nutrients. It's also very sturdy, meaning that once plants get a strong foothold, it's difficult to uproot them. I've never read anything to support this, but I hear gardeners with loose soils complaining a lot more frequently about moles, voles and gophers than gardeners in heavy clay soil.


Clay tends to be slow to warm in the spring and can retain heat in the summertime. Those aren't really issues in my region since our growing season is long, approximately 220 days, but it might be something to work around in shorter season areas.



Quick ways to evaluate clay content


I think the Mason Jar Soil Test is the best at-home way to assess the soil type but when there isn't time to do that there are some other ways to get an idea how much clay soil has.



Get a fistful of the dirt or compost and see if it holds together when it's wet. If it holds like a ball, you have clay. It becomes more crumbly if it has a high organic matter content or if it is more loam-like than clay.


The ribbon test is another way to see how clay-ish soil might be. If it holds together in a ball, go one step further by squeezing it between your fingers. The longer a ribbon of clay that can be created this way, the higher the clay content. In my case, much of my soil is like modeling clay so I can make a long ribbon, but in "improved areas" the soil has a consistency more like Play-doh so the ribbon doesn't get as long before it begins to crumble.


The stick figure made from clay really has no bearing on evaluating soil content. I have to keep my sense of humor about challenges and this is just an example of me laughing at the situation instead of getting upset about it. I've dubbed him "Clay Dirtman" and he's going to be my soil mascot!

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The 
Collected Seed