Healthy Soils for Healthy Vegetables

Written December 12, 2012, published in late December, 2012, all photographs by Kathleen Sayce

Soil health for vegetable gardens is more precise than for ornamental gardens and native plants. Most vegetables are annuals or biennials, living only one year, or over one winter.  All of are from other places and climates, with nutrient and soil needs considerably different than local soils can provide. Vegetable plants need:  Deep, open, well-aerated soils with soil carbon, diverse minerals, sunlight, warmth and regular water. With these, they grow quickly into tender, nutritious and edible foods; without them, vegetable plants struggle, easily fall ill, and fail to thrive. Vegetables generally are not shade plants, especially along the raincoast; warmth and regular watering are needed for vegetables to grow well. 

Well-grown vegetables are able to resist weather, diseases, insect pests, and have high levels of minerals, proteins and other plant compounds. This photo of Red Russian Kale was taken in Jim Karnofski’s vegetable garden by Kathleen Sayce.

Soil Carbon

As with other kinds of plants, vegetable plants need soil carbon. The forms that are the most usable for vegetable plants are not aged wood chips or forest debris, but well prepared compost with humus, and biochar (biologically activated charcoal). Vegetable plants use soil carbon throughout their root growing areas, so gardening practices for optimal plant nutrition incorporate carbon of several kinds throughout the soil profile. Gardeners work carbon into the soil with a rototiller or shovel, add layers to the surface, side dress plants, and amend planting holes. They also fallow garden sections every few years, planting cover crops to put more carbon back into the soil. 

Carbon promotes soil health by giving soil organisms food to eat (carbon) and places to live (cellulose scaffolding). The one drawback is that, being formed of cellulose (wood), most forms of compost break down quickly. So gardeners need to add compost regularly, year after year. Only humus, a brown, clean-smelling, somewhat sticky substance, persists for decades to centuries in soil. Compost piles can form humus if clay and local soil are added to each layer. 

Compost with charcoal added is dark colored, and is now ready to go into the vegetable garden.  Photo of one of Jim Karnofski’s compost bins.  

A second soil carbon material, biochar, is charcoal that has been activated with compost or soil microbes. Biochar has an advantage as a soil amendment: charcoal is stable in soils for centuries to millennia. When gardeners add biochar, this is a permanent improvement in the soil. Add biochar along with compost, and over time, you will have the same productivity with less compost. 

Making Biochar

When wood is burned, charcoal is formed during the burning process. If burning is complete, the wood goes to charcoal and then to ash. Starving the fire of oxygen (a process called pyrolysis) promotes charcoal formation and keeps the fire from consuming all the wood. Innovative pyrolysis burners are being developed at backyard and industrial scales to produce large amounts of charcoal with minimal amounts of ash. When the charcoal is wet and cold, it can be added to compost to be inoculated. See  HYPERLINK "http://www.biochar-international.org/" http://www.biochar-international.org/ for biochar producing devices. A short video for an introduction to home charcoal making is on You Tube at  HYPERLINK "http://www.youtube.com/watch?v=dqkWYM7rYpU" http://www.youtube.com/watch?v=dqkWYM7rYpU .

Freshly made charcoal is ready to go into the compost pile when it is wet and cold, and broken into small pieces. 

Mineral Nutrition

The second soil management practice for optimally healthy soils is to use soil tests to determine what minerals are needed, and then to add those missing minerals in the correct amounts. Soil tests are inexpensive, and a simple way to ensure a garden is not over-fertilized with some minerals and too low in others. It’s a good gardening practice to test soils in your vegetable garden and adjust your fertilizer program every year. Minerals can be added as rock dusts, algae extracts, and other forms.  The differences in terms of productivity can be staggering; I’m not talking ten percent increases or even twenty. At times, improvements can be on the order of multiples, as measured by plant weights or volumes, fifty pounds of potatoes instead of twenty, for example.  

Jim Karnofski, local vegetable gardener and retired nurse, has delved into soil mineral nutrition as a neighborhood soil analyst, and is wiling to teach anyone interested in learning the details how to decipher soil test results. He also makes custom nutrient blends for specific soils. I tested my soils a few weeks ago, after years of adding carbon, trace minerals, and organic fertilizer blends. I found that my soils are surprisingly low in boron, manganese, sodium, copper and sulfur. Jim composed a custom blend to meet the nutritional deficiencies based on the soil test. I’ll add a portion of these missing nutrients every few months, test again in coming years, and keep adjusting minerals to improve my soil. A new book by Steve Solomon, The Intelligent Gardener: Growing Nutrient-dense Food, goes into splendid detail about vegetable nutrition. 

The sum of all of these actions (adding carbon, testing soils and adding mineral nutrients) is to have optimally healthy soils. Healthy soils produce healthy plants, able to resist disease, drought and insect predation. In turn, healthy plants produce nutrient-dense vegetables and fruits, which are better foods for us.  Many chronic human health conditions go away when people make the change to eating fruits and vegetables grown on optimally healthy soils. I think we’d all like to live healthier lives, and my personal task for the New Year is to promote soil health, so as to promote human health. 

Healthy soils for Garden Plants

Written November 30, 2012, published December 2012

Hand in hand with good plant choices, and planting at the right time (fall) to fit the local climate, is promoting soil health.  There are two paths to take; one is for native perennials, shrubs and trees, and the other is for vegetables. I’ll discuss vegetable soils later. Today, my focus is on ornamental gardens, especially native plants––perennials, shrubs and trees–-and the soil these plants need to grow well. 

On a hillside under pines, Evergreen Huckleberry, Vaccinium ovatum, and Soft-footed Sedge, Carex leptopoda, grow in thick layers of wood chip mulch. Photo by Kathleen Sayce

Our climate is a curious one, with wet winters and dry summers. Wet winters mean that it’s difficult for soils to hold onto nutrients, many of which are water-soluble. Long months of cold rains mean that nutrients wave at plant roots as they wash past and out of reach. Worse, those long wet months bring the ground water table up to the surface in low areas. Roots of most upland plants do not grow in water due to low oxygen levels. The result is these root systems are relatively shallow, and nutrients wash past even more quickly. Also, during severe windstorms, plants with shallow roots are more likely to blow out of the ground. Due to a long wet season, local soils are also acidic; native species tolerate and even prefer this acidity. 

Streambank orchid, Epipactis gigantea, is growing in a low wet swale, amended with compost and aged wood chips. Photo by Kathleen Sayce

In nature, soils store carbon in several forms:  living and dead wood, including logs, branches and twigs, or thatch, and living and dead roots. Many species of fungi and bacteria live on these materials. Wood, roots, branches and twigs are composed of cellulose, the most common biopolymer on the planet, which is made by living plants from sugars formed during photosynthesis to shape cell walls. Those sugars and celluloses are the plants’ building blocks and trade goods. They trade sugars with bacteria and fungi for water and nutrients. 

In thick layers of woody mulch, Stropharia fungi produce mushrooms, the fruits of soil mycelia. Photo by Kathleen Sayce

Different species of fungi live on heartwood, greenwood, cambium, bark, roots, and dead wood. Specific fungi live on living roots, dead roots, and on duff materials––twigs, needles and branches that fall to the forest floor.  Specific fungi associate with specific shrubs and trees, connecting via their mycorrhizae (fungal filaments in the soil, which are often whitish and look like thin fragile roots) with plant roots, to share water and nutrients. 

Mushrooms are abundant in garden soils with ample carbon, such as aged wood chips.  Photo by Kathleen Sayce

The fungi get simple sugars from the plants, and the plants get minerals in return. There may be bacteria in association with both that fix nitrogen, and also share with fungi and plants for sugars.  Animals that live in the soil eat roots, fungi and bacteria, and are eaten by other animals. Their bodies are food for other bacteria and fungi. Soil ecosystems are largely hidden from us by virtue of size and location, as most soil organisms are microscopic and all are out of sight underground. 

To promote healthy soils for native plants, then, it is not sufficient to provide water and fertilizer. In fact, nitrogen fertilizer by itself, without the supporting structure of soil carbon and soil organisms, throws soil out of balance, causing soil carbon to be eaten and further depleted in the soil, year after year. 

Balance is restored to the soil by adding several forms of carbon:  compost, biochar (biologically activated charcoal), tree litter and wood chip mulch. As I mentioned at the beginning, this is not a soil designed for vegetable gardens, but for native trees, shrubs and perennials, species that have lived here for thousands to millions of years. 

Blue-flowered tall camas, Camassia lechitlinii, is growing in a plant bed that was widened; the thick wood chip and compost layer is now ready to plant. Photo by Kathleen Sayce

There are efficient ways to feed these forms carbon to the soil. One is to mix in compost and biochar around the root zone in the planting hole when you put in plants. The second is to layer all of these materials on the surface, year after year. Carbon promotes the growth of soil organisms, which in turn collectively improve soil health, help it retain nutrients and water. 

Wood chips can go on the surface of the soil in a mulch layer. These aren’t fresh from the chipper, but aged chips, piled and kept damp until well-colonized by soil fungi. The piles are aged for a year or more, until fungal mycorrhizae (visible as small white threads) have thoroughly spread throughout the pile. Once a soil is on its way to improved health, in alternate years spread compost or wood chips. 

How do you know there’s enough carbon on top of and in the soil? You will see fruiting fungi (mushrooms) during the wet season. When mushrooms appear, they tell you that the soil has enough carbon to be reasonably healthy. The gain is in the garden: plants need less summer water, grow well without added fertilizers, flower abundantly, set seed, and resist drought and disease. 

Plant in the Fall for good growth the next year

Written November 4, 2012, published mid November 2012

As an ecologist who likes to garden, I’ve worked and reworked the design and plants in my garden for years, starting with a traditional older coastal garden with lawns, rhododendrons, camellias and roses. I tried perennials and cottage-style beds, then a more Mediterranean-style garden with sages, lavenders, rosemary, bulbs, rockroses, and no summer irrigation.  This led me to focus on soil health, lower impact gardening, and to growing more native plants. I always had a few in my garden, especially evergreen huckleberry and sword fern. Now I have many more, and the result is a hardy, tough garden, full of flowers, bees, butterflies and birds, that needs little to no summer water. 

Common Camas, Camassia leichtlinii, grows 30-40 inches tall, with light blue to dark blue flowers, and is very attractive to native bumblebees and early butterflies. Camas grows in spring wet /summer dry soils, in full sun. Photo by Kathleen Sayce. 

Our wet winters and dry summers aren’t common around the world. Places with some rain all year round, or with dry winters and summer rainfall, cover most of the planet’s landmass. Our local area is considered a cool Mediterranean-type gardening zone. In Mediterranean-type climates, the driest time of year coincides with the most sun and heat. Our summer and early fall weather tends to be quite dry. Small patches of this climate occur all over the world at moderate latitudes, yet the total area does not cover more than ten percent of the planet.  

Pacific wax myrtle, Myrica californica, is an evergreen shrub to small tree. It grows in full sun to part shade, and can tolerate both damp and dry sites. Birds like its waxy berries. It makes good hedges for screening, to 10-15 feet tall, and mixes well with shore pine and salal in hedgerows. Photo by Kathleen Sayce

How our native plants cope

Native plants in the maritime Pacific Northwest compensate for dry summers by timing bud-break, leaf-out, flowering and seed production to seasonal water. These plants also engage with soil fungi with roots; this improves access to nutrients and water. Native plants often have two distinct growing periods, spring and fall, and may go partially dormant in late summer when water stress is the greatest. Many flower in spring, set seed by early to mid summer, and wait out the dry season partially dormant; then they put out new roots in fall. They are ready to grow if rain falls during the dry season, but survive if the weather stays dry.  

Kinnikinnick, Arctostaphylos uva-ursi, is a low growing evergreen groundcover with pink flowers and red berries. It grows in full sun to part shade, in damp to dry sites, and mixes well with heathers and salal. Photo by Kathleen Sayce

Plant in the fall

The best time to plant is in autumn––after the start of rain, usually October or November. As soils cool down and rain starts, plants’ roots begin to grow. They grow new roots when soils are moist and temperatures are at or above 40 F. In mild winters, this can be almost all winter long.  The bigger the root system by next spring, the more that plant will be able to grow that summer. Fall planting decreases the amount of water needed the next summer because these root systems are bigger than if planted in spring, just before the dry season starts. Reduced watering the next summer by planting the prior fall sounds pretty good. Less watering during the dry season is also very efficient. 

Salal, Gaultheria shallon, is an evergreen shrub that can be kept low or allowed to grow more than six feet tall. It has early pink flowers and edible dark blue berries, and grows in damp to dry soils, full sun to part shade, and mixes well with other shrubs and groundcovers for hedges and woodland plantings. Photo by Kathleen Sayce.

Food for native animals

There is an important ecological reason to use native plants: to support native animals. Insects, birds, small mammals, and the animals that feed on them, are ultimately dependent on native foods. Yes, there are introduced plants that can be eaten by generalist native animals, particularly deer. By and large, most native animals key in on a few native species. If you want butterflies, bees and other pollinators, birds, amphibians and mammals to hang around your yard, put in native plants. Large areas planted to introduced species are ecological deserts for native animals. There’s nothing for them to eat. 

There’s an excellent book on this subject by Douglas Tallamy, Bringing Nature Home, which contains a wealth of details about the complexity of native plant communities, the animals they are food for, and the choices we have to encourage, or discourage, native ecology in our own yards. He writes about Delaware, but the principles are the same here in the Pacific Northwest. 

If you dislike hauling hoses around, and prefer a garden that can take care of itself in droughts, torrential rains, and snow, then select native plants over introduced plants. There are hundreds of species, including trees, shrubs, perennials and bulbs. The result is a garden that is more attractive to native animals, including butterflies, bees and birds, which needs little to no summer water, and survives our wet cold winters in good condition.  Don’t forget the time of year to put in those native plants––in fall. 

Indian rhubarb, Darmera peltata, flowers in the spring, then the leaves come out afterwards. It prefers soils that are wet to damp year round, in part sun to shade. Photo by Kathleen Sayce