Pulling Back the Woodchip Cover

Over the last five months we've covered the old lawns and area under the oak tree with wood chips. Our landscaping plan is not to simply cover everything with mulch and walk away. Instead, we hope to improve the infrastructure by restoring and augmenting the soil. We've had some good winter rains this year which should also help.

Wood chip cover

Section 1: moist soil and healthy root (an earthworm escaped)

Is any of this actually helping the soil? This week I pulled back the woodchip cover to see what's happening underneath. I didn't know what to expect (if anything), but it can be satisfying to monitor progress. My plan was to pull aside the chips in three different sections and see what was happening "under the covers".

Section 2: loose clay soil

Section 3: decomposing wood chips

The soil was moist, which was expected since we've had several good storms pass through the San Francisco Bay Area in the last several months. In one section, the moss was no longer green (but its root mat was still intact), an earthworm raced for cover in the soil, and a nice healthy root was visible. In a second section, the clay soil broke up easily. In a third section, some of the lower-level wood chips showed a bit of fungus (I think this means decomposers are starting to work on them to break down the wood), and a bulb was pushing up through the mulch. Finally, under the bird bath, I found a little colony of white fungus (I think). I'll check again in several months to see what happens as the weather warms and turns dry. Stay tuned!

Decomposers under the bird bath

Wood Chips Under the Oak

More wood chips! This time we're focusing attention on the area under the big oak tree. Over the years the soil has become compacted under the tree, and some its roots are growing above ground. The area is covered with a lovely green moss during the wet winter months (but is typically brown and dry the rest of the year). Our arborist recommended that a covering of wood chips would help with soil restoration.

More wood chips from BeeGreen

I ordered seven cubic yards from BeeGreen, which is quite a pile of wood chips (my previous order was five cubic yards). Luckily I had help moving all that material to the yard under the oak tree! The wood chips will help conserve moisture in the soil, as we transition to the dry summer and fall season. The chips will also break down over time, decomposing into the soil.

New wood chips under the oak in the background (older chips in the foreground)

I'm hoping for another winter rain to "water in" the new chips (maybe next week). I'm also hoping the squirrels will be able to find their acorn stashes from last fall, now that their usual landmarks are covered. From experience, I know that the birds continue to visit the bird baths and feed on insects, even with the wood chip cover. I'm sure the squirrels will adapt as well.

Wood chips in the fore- and background (a band of mossy green remains)

Air Spade

Soil compaction results when soil particles are squeezed together, eliminating air space. This makes it harder for water and air to infiltrate the soil, and for roots to grow and take up water and minerals. While researching methods of restoring compacted soil in Soil Restoration Under the Oak, I came across an arborist tool called an air spade (also known as an air knife). 

The air spade is powered by an air compressor, and moves soil away from tree roots at super-sonic speed without damaging the roots. The video shows several tree care applications, including vertical mulching around marker 0:54, and soil aeration around marker 2:25. Note that this is not a product promotion, just a very informative video. You can find more examples by searching the Internet using a variation of "air knife for arborists".

In our case, our arborist did not recommend something as powerful as an air spade, since the compacted soil under the oak tree is not in a foot traffic area. The wood chips are sufficient to start.

Learn more:

• Keeping Native California Oaks Healthy, by Bruce W. Hagen, Forest Pest Specialist, Forest Pest Management Program. California Department of Forestry and Fire Protection, Tree Notes, Number 7, June 1990.
• What is a Super-Sonic Air Knife, by Conner of Root Cause Seattle (video).
• AirSpade for Arbor Applications

Soil Restoration Under the Oak

 The soil under the oak tree needs some help. The soil has compacted over time, and some of its roots are exposed above ground. The root zone is not a foot traffic area, but over time, gravity and natural drainage have eroded and compressed the soil. We stopped irrigating the area years ago. The lawn died, and was replaced with moss (beautiful during the rainy winter season, but less so during the dry summer months). It's good that we stopped watering, since too much water during the warm season invites disease for oaks.

Majestic oak tree trunk and limb

I scheduled a consultation with our arborist from Brende and Lamb to discuss the health of our oak tree, and get the scoop about soil restoration. Our landscaper had expressed concerns about several small cavities and cracks in the bark at the base of the tree. We've been letting the oak leaves collect under the tree in a natural duff to jump start the soil restoration process. I wondered whether we could do more, such as bring in a load of wood chip mulch (see Wood Chips Everywhere!), or aerate the soil using a soil aerator or an air spade (a.k.a, an air knife). I also wanted to discuss irrigation, since we have plans to modernize our old, broken system.

Small cavities in the oak bark go back several inches

Our arborist has been monitoring and pruning our oak for years. He opined that the cracks in the bark were part of the natural growth pattern, and that the small cavities were probably fine since they did not harbor standing water. Limb attachments in a v-shape are more worrying, since they can trap moisture that can lead to rot (versus u-shaped attachments, where water rolls off more easily). He recommended that we bring in wood chip mulch to protect the soil, and encourage its restoration. He also recommended that under our big trees, a soaker hose  is a good irrigation solution (even oaks appreciate an occasional (monthly) drink of water during the hottest months).

Ridges and roots under the oak tree

Optionally we could aerate the soil. He thought the air spade would be overkill, since our oak is not in a high traffic area. But he described a method of using a deep-root irrigator to create holes in the soil, and then filling them with organic mulch to enable the exchange of oxygen in the soil. Many tree services offer the service, but it would be quite expensive for the area under our oak. Instead he recommended doing it ourselves - chipping away at it over time, especially during the rainy season when the soil is typically moist. It's a pleasure to meet with someone who knows and loves trees. We now have the information we need for the next steps!

Wood chips in the foreground, and leaf duff beyond

Wood Chips Everywhere!

I recently ordered five cubic yards of mulch as part of our soil restoration project. We've neglected our yard over the past several years, and are now doing something about it. Our hope is to create a wildlife- and people-friendly sanctuary here in the Oakland hills. See Soil Restoration and Horse Bedding to learn more about the transformation. 

Fresh delivery of wood chip mulch

I researched several free sources of mulch, including ChipDrop. They match up arborists with homeowners, to recycle mulch for free (or a donation). I love this idea. But the quantity could vary from three cubic yards to 12 cubic yards, and delivery could be at any time the landscaping team is in the area. Between keeping people from parking in front of the delivery zone, coordinating with gardeners, and the unpredictable quantity, it seemed more sensible to start with a trial run on a smaller scale. 

Expert delivery

We used BeeGreen Recycling & Supply, located right here in the San Francisco Bay Area. BeeGreen has a good selection of landscape materials, including bark, mulch, rocks and aggregates, soil and amendments. They also recycle local materials, and they schedule a two-hour delivery window. I chose a small bark in a nice earth tone, and used the Material Calculator to determine the quantity we would need to cover the area. I'm hoping the small-sized bark decomposes more quickly than the larger size, releasing nutrients into the soil.

Wood chips along the patio wall

Wood chips covering the historical lawns

Our gardener spread the wood chip mulch over the former lawn area, and in a strip along the patio wall. Now we're hoping for rain to help speed decomposition and soil restoration process!

Horse Bedding

This fall we're working with our gardener and a landscape consultant to enrich the soil in our yard. We recently received a delivery of about 12 cubic feet of horse bedding from a nearby stable. It is comprised of the chips and straw used to line the stables, and horse manure, and is a coup for our Soil Restoration project. 

About 12 cubic feet of horse bedding

We postponed its delivery until the heat wave and forest fire smoke had subsided, and cooler weather arrived. Surprisingly the bedding has no unpleasant odor. Instead, it has a mild, earthy smell that is quite pleasant and natural. 

Horse bedding is gold for the soil

Our landscape consultant spread some of the bedding on a section of the old lawn that has lost all of its topsoil. The wood chips will protect the compacted soil, and eventually break down. The manure, which contains some of the nutrients (nitrogen, phosphorus, and potassium) that animals consumed, will also break down and become incorporated into the soil. 

Horse bedding on the old lawn

Horse bedding under camellia shrubs

He spread another batch of the horse bedding under the camellia shrubs that are in the back of the house. A nearby Japanese maple and magnolia tree will also reap the benefits. This enriched mulch will contribute to the process of process of soil restoration, especially when the winter rains start in a month or so.

Soil Restoration

 I'm afraid we've neglected our garden for too long. Between trips to Seattle, Alaska, and the desert, explorations in the regional parks, and researching and filming "plants to dye" for projects, our yard has suffered (but no regrets for all that life lived!). Add a long drought several years back, a broken sprinkler system, and a rigorous career, and things are looking a little ratty. Part of this was intentional – the first phase of converting from a water-thirsty garden from yesteryear to a modern native plant and wildlife friendly garden. The idea was to practice survival-of-the-fittest gardening for awhile, and see what survives!

Brown, compacted lawn

We'll start with the remaining bones of the original garden, and work from there to create the next phase of the garden's life. I actually like what remains - the oak tree is a major focal point. The native toyon, hawthorn, and prunus shrubs in the lower yard are holding their own, and provide a screen and sound barrier for busy traffic and a habitat for birds. The junipers and sedges are also healthy. The camellias are a little leggy and scruffy (but may be at the end of their life cycle). The pittosporum and tulip tree by the fence look pretty good (their roots may be pirating water from our neighbor). The lawns are brown most of the year, but the embedded moss typically greens up in the rainy season and looks quite beautiful. Quite a few flowers come up in the spring from spring rains.

On the negative side, the soil where the lawns once thrived is compacted and needs restoration. So does the soil under the oak tree (carefully). We're teaming up with our maintenance gardener, and a gardening consultant who has helped clients all over the Bay Area with their gardening projects. One of our first steps is to bring in mulch, organic matter, and fertilizer to enrich the soil. We're looking forward to the transformation, and will keep you posted!

Soil Compaction - Step Four

Back to my soil recovery project for an update. Recall in Soil Compaction Recovery - Step 3, my cover crop was fully developed. Soon after that report, I cut down the cover using a machete; and turned under the soil to break it up and incorporate the roots and plant material. As an experiment I left a corner section unturned, with the idea of planting seeds in the soil without disturbing it. I have read that some farmers are using this technique on a large scale to help preserve soil.

The soil is prepared.

In July I planted several varieties of beans and peas in this small 10 x 10 foot plot. I fertilized with organic Alaska fish fertilizer, laid out my rows, and planted seven types of seed. I was pleased at how friable and tillable the soil was after just one cover crop. Per usual, I had a few experiments going, including: (1) using seeds for 2012, (2) using seeds from 2004, (3) using seeds from a variety of growers (Burpee, Ferry-Morse, Cornucopia, Seeds of Change, and NK Lawn and Garden), and (4) using Heirloom seeds that I harvested from my bean crop last year.

Planting lines.

I expanded my drip system to the new plot, by adding a second line to my hose system, and and a switch between the two lines. Eventually I plan to install a more permanent, and automated, drip system, but am content for now to learn all I can about drip systems and how they work.

Second drip line added.

I also reused my bamboo trellis from last year - moving it out of the raised bed, and installing it in my recovery plot for the bean and peas. The trellis is looking a little shoddy, but the bamboo, plastic cinches, and webbing appeared strong enough to handle another season.

Repurposed bamboo trellis.

Soils in Our Environment

Soils in Our Environment, by Duane T. Gardiner and Raymond W. Miller, is a great book for learning about soil. This book is for soil nerds only, probably not the typical gardener. But if you are up for it, you can learn a lot about soil from this book. We used it as the text for the Soil Management class taught by Dr. Ed Brennan at Merritt College.

The first half of the book covers soil composition; physical, water, and chemical properties; organisms; soil formation and morphology; and soil taxonomy. That gives you a good background for understanding other topics like nutrition, fertility, erosion, and irrigation. The book describes how to read soil surveys to better understand your specific soil, and provides specialty topics like soilless culture, salt-affected soils, and soil compaction (a favorite topic). The Appendices provide information about the many graphics, references for measuring soil volume and moistness, a refresher on the periodic table (handy, since it had been decades since high school chemistry), and a glossary of term.

The book is well written and nicely illustrated with photos, charts, illustrations, and graphs. Turns out, all that science is pretty interesting, and really useful for finding out more about practical gardening things, like how to deal with clay soil, acidic soil, erosion, and so forth. I recommend this book as a reference.

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.

HTML Tables

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.

HTML Tables

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.

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.

Street Trees in Santa Cruz

Santa Cruz implements fabulous planters for their down town street trees. They are basically wide, raised beds surrounded by protective railings. This enables the roots to spread to establish a good foundation, enhances soil aeration, and reduces soil compaction. Multiple trees are planted in a single planter, which is similar to nature where trees often grow in groups or groves. The planters provide an environment for mature trees, which add shade and beauty to the street.

Large street tree planter in Santa Cruz -
corner of Walnut and Pacific Avenues

These planters contrast with the small square of soil that is typically allotted to street trees. Root structures are covered with concrete, so roots are confined, walked over, and the soil is not properly aerated. In this condition, tree roots often break up the pavement causing uneven and dangerous surfaces for pedestrians.

Santa Cruz has a strong program of urban forestry, and a commitment to incorporating street trees in their landscaping to promote a sense of place and relief in the urban landscape.

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.

Arborist to the Rescue

It's the retaining wall

Our arborist came to assess the health of our trees, and give an estimate for pruning some of the big trees. This is something we do every two or three years to keep the trees in scale with the property, and ensure safety.

He also gave a diagnosis for the death of the three maple trees - last year’s broken sprinkler and the retaining wall conspired to flood the roots and drown the trees. Roots need oxygen in the soil in order for the tree's hydraulics to work. The water and oxygen exchange draw water up the trunk and out through the leaves. With flooded roots, the tree suffocates.

The soil may have also become compacted. Soil compaction can be a problem with clay soil. The solution to this is aeration to increase pore space in the soil, enabling a better exchange of water and oxygen. The process involves using an aerator to dig holes in the ground every 18 inches, and fill the holes with compost.

Once we remove the trees , we'll be  planting new maple trees, because we miss their beauty, elegance, and grace. 

Clay Soil Shocker

If you are from a region of the country with loamy soil, or one of its variations, the clay soil in the San Francisco Bay Area can be a shocker. Drainage is slow; soil turns to sticky mud when saturated; then clumps or is brick hard when it is dry.

But, the clay soil structure also attracts nutrients and holds on to water, which is ideal during the summer dry season. With a little work and knowledge, and some new practices, you may come to appreciate clay soil properties. Some ideas worth exploring:

• Garden with raised beds or containers.
• Amend the soil to increase pore space, and improve drainage.
• Plant a cover crop or mulch to prevent soil from becoming compacted.
• Use native plants that are are adapted to clay soil.

For a good web article about working with clay soil, see Keith Baldwin's web article "Improving Clay Soils" in Fine Gardening.

Use containers or raised beds for plants that do not thrive in clay soil.