Soil Compaction Recovery – Step 3

Step 3 of my soil compaction recovery plan may seem like a repeat of step 2. Not really. I think it is important to acknowledge nature’s part in the process. Sure, I prepared the soil and planted the seeds, but while I was traveling in the fall, celebrating Thanksgiving and Christmas, watching weird plant movies in January, working several major deadlines at work, and studying trees during the spring semester at Merritt College, nature was quietly doing the real work.

Cover crop in November.

I checked progress over time, in between rain storms and when it was light enough (difficult when I was leaving for and arriving from work in the dark). Each time I was thrilled at the progress, and excited to see a whole different palette of plants grow. I grew up in Southeastern Alaska, so I’m not exactly a city girl. But we didn’t have crops. What can I say - it’s a thrill! I rooted around the soil a bit also. I can’t say that I can report anything major, but the soil remained broken up and porous.

Cover crop in late May.

However, things did get out of hand between March and May, when I was steeped in travels to Southern California and Spokane, deadlines at work, and my Tree ID class. Basically, I did not plough under my crop in February as I should have (or in March, April, or May). I’m afraid Farmer David would be aghast, and lecture me that I’ll be pulling pea and vetch weeds for the next couple of years. But my real goal is improving the soil – that part may still be a success.

Soil Compaction Recovery – Step 1

About a year ago, I came up with a plan for recovering from soil compaction in a section of my garden. Recall we had removed an overgrown pine tree and then never planted anything to protect the healthy soil. The clay soil had become compacted, unsightly, and unusable. Part of my plan to fight soil compaction was to break up the soil and add organic material.

The soil has been broken up in a 10' x 10' section of the yard.

In September, I started to execute my plan. The patch of dirt is relatively small, so I broke up the soil manually with a shovel. I did wet the soil lightly with a hose, and then waited a day or so. Once the dirt had softened, I turned the soil, breaking the large chunks into smaller ones to increase pore space. If this had been a larger area, I would have borrowed a tool from the tool lending library to help with the process.

Organic chicken manure amendment.

Next, I added some organic matter, in this case chicken manure, and allowed it to set for a couple of weeks. I also created a small path of wood chips to the compost bin, on the border of the area I was restoring, as a buffer against further soil compaction.

A bark path to the compost helps prevent
additional soil compaction.

Fighting Soil Compaction

I have done some research into how to fight soil compaction, so I can come up with a game plan for restoring my compacted soil to healthy, productive soil. The primary thing I learned is that it is difficult to restore compacted soil, and the best solution is prevention. Great. But there are some guidelines and principles I can use:

• Break up the ground to start the process of adding pore space.
• Don’t work with wet compacted clay soil. The molecules can slip into even more compacted configurations. Let the soil dry out a bit.
• Add organic matter, such as compost, to the soil. Work the organic matter into the top few inches of soil. Organic matter breaks down quickly, so this is an iterative process of adding organic matter, working it in to the soil, letting it break down.
• Use mulch to cover soil if you do not plan to plant immediately.
• Keep people from walking over the soil, to prevent further compaction. Ideally provide paths where needed.
• Use a cover crop to protect the soil, and even develop it. In agriculture, farmers plant a cover crop, such as alfalfa, between other crops. A crop like alfalfa, a legume from the Fabaceae (formerly Leguminosae) family, can actually grow in poor soil, and fix nitrogen in the soil to enrich it. Cut the foliage at the end of the growing season, but leave the roots in the soil to improve aeration.

Agriculture uses cover crops to hold the soil in place,
 and enrich the soil. The same principle can work
in the personal garden.

I learned a lot about soil from the Soil Management class I took from Dr. Ed Brennan, and from a soil compaction project I worked on with team members in the Arboriculture class I took from Jocelyn Cohen, both at Merritt College. Stay tuned to see if this research and knowledge pays off!

Soil Compaction

Healthy soil is a blend of decomposed minerals, organic material, microorganisms, and pore space, which provides oxygen. Soil characteristics include color, structure, and texture. Soil color is influenced by the parent mineral, for example, a red soil may indicate iron. Soil structure describes how the soil arranges itself in aggregates, for example, clay soil dries in hard, dry clumps. Soil texture is the composition of sand, silt, and clay, for example, sandy soil drains quickly, where clay soil holds on to water. Healthy soil should be teaming with life to provide a home for trees, shrubs, and plants.

Soil can become compacted, which means pore space is reduced or eliminated. This may happen purposefully during construction of a house, where soil is compacted to stabilize the soil. This can also happen when raindrops strike bare ground over a period of time, ground is used as a path or road, or ground is left fallow with nothing growing in it. When soil becomes compacted, water runs off and does not penetrate the soil; roots cannot move through the soil as easily; and the water and oxygen exchange between soil and roots cannot take place. The microorganisms that are required for healthy soil cannot live in this condition. The soil becomes unusable.

Soil has become compacted in a section of the yard
where a tree was removed.

My garden has an area where the soil has become compacted. We took out a pine tree several years ago that had grown out of scale for the property, and was growing close enough to the house to become a fire hazard. We cleared out the tree roots, but never replanted anything in the area. The soil has become compacted, with nothing growing on it except for a colony of moss which revives during the winter rains. The rest of the year, the soil is like a clay brick. I’d like to restore this patch of ground to life.