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 2

The next part of my soil recovery plan was to plant a cover crop, similar to what farmers do to protect the soil. I had learned more about cover crops when I visited Oak Hill Farm in Sonoma County last fall. They use an organic cover from Le Ballister’s Seed and Fertilizer in Santa Rosa. They plant the cover crop in the fall, typically in October, and then mow it down and incorporate it into the soil in February.  Farm Manager David Cooper had admonished it is important to mow before the seeds set.

100% Organic Plowdown cover crop mix.

Pea, bean, barley, oat, and vetch seeds.

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I ordered 15 pounds (the minimum shipping order) of the 100% Certified Organic Plowdown Mix. The mix includes Magnus peas, bell beans, barley, oats, and vetch. Many of these are in the legume family, which means they set nitrogen. I seeded densely in my zeal, but I’m sure a seasoned farmer would know better.

Seeded in.

Watered in.

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I tamped down the seeds into the soil as instructed, and then watered in. Within a couple of weeks I was rewarded with bright green new growth, and on my way to repairing the compacted soil.

The cover crop emerged in October, a couple of weeks after planting.

Succession

In Designing California Native Gardens, Alrie Middlebrook describes her use of succession (moving through a series of simple-to-complex planting stages, culminating in a final stage) in her garden designs. For slower growing shrubs and trees, she recommends planting them with ample spacing, so they can grow to their mature size without overcrowding, and filling in with shorter-lived grasses, bushes and flowers. She gives the example of establishing an oak woodland garden in a hot area of a yard. While the oaks were getting started, she planted chaparral species that could tolerate the heat, and then started to introduce oak woodland understory plants as the oaks became established and their watering needs changed.

I saw succession at work while growing up in Southeast Alaska. A marker at the Mendenhall Glacier Visitor Center indicates the location from which the glacier had receded only a hundred years before. The glacier left behind barren, ground bedrock; over time moisture- and air-borne soil particles began to accumulate. Early plant species—such as fireweed, grasses, and alders—moved in. Alders can live in poor soil, and fix nitrogen, so they contribute to building the soil. Over time, spruce trees replaced alders – shading them out. A new understory of shade-tolerant plants emerged, such as fern, horse tails, moss, devil’s club, and Indian rhubarb. During this process, organic material accumulates and decomposes, further enriching and developing the soil.

Succession at work - this peninsula at Mendenhall Glacier used
to be barren rock just several decades ago.

The key ideas for using succession in the home garden are: (1) enrich the soil naturally, and (2) design an attractive short-term garden that allows slow growing trees and shrubs the space and time they need to get established.

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!

Give Peas a Chance

March 17 (Saint Patrick’s Day) is the traditional day for planting peas, but I typically plant them in late May in the San Francisco Bay Area. We usually enjoy peas well into September, when we are experiencing our hot, dry season.

Why are peas so great to grow? Not only are they easy to cultivate and eat, but they can be planted in very poor soil. Peas are in the legume family, which includes nitrogen-fixing plants. These plants “capture" nitrogen out of the air, and “fix” it into the ground. Peas provide their own fertilizer! The plants require rhizobia bacteria in the soil. The nitrogen cycle is one of those beautiful mysteries of the garden.

Last year I planted Super Sugar Snap Peas
from Renees Garden (reneesgarden.com).

We enjoyed peas for several months.