Monthly Archives: July 2015

Summer Priorities

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My first summer priority in the garden centers on weeding, and my regular resolution to walk around with a weed identification book. My desire to know the names of garden plants extends to the weeds that know so well how to grow under all conditions, and without nurture.

One new arrival is the Black Nightshade (Solanum nigrum), which is a relative of several desirable plants, including potatoes, tomatoes and peppers. It is common throughout California.

7-17-15 - Solanum_nigrum

This weed grows up to four feet tall. UC’s Integrated Pest Management website describes its leaves as follows: “The first true leaves are spade shaped with smooth edges and the lower surface is often purple. Later leaves are increasingly larger, egg shaped, dark green, often purple tinged, with a smooth to slightly wavy edge, and covered with short non-glandular hairs and some glandular hairs.”

The plant produces small, star-shaped white flowers that develop in blackberries about one-quarter inch in diameter. Some varieties have edible berries, but their taste is not good enough to offset risking that you have a different variety in your garden.

To its credit, the Black Nightshade pulls up easily.

Another member of the Solanaceae, the tomato, is also flourishing in my garden. This year, I planted two cherry tomato varieties from Love Apple Farm, chosen at San Francisco Flower & Garden Show. A volunteer from last season, ‘Sweet Million’, popped up, so with minimal watering, I have an abundant harvest of cherries for salads and casual snacks outdoors.

Then, a friend gave me a seedling of a Black Krim (Solanum lycopersicum), a heirloom tomato from Russia. This plant needs consistent moisture. If the soil is allowed to dry out between watering sessions, the fruit has a tendency to crack.

Tomato fanciers relish its “rich, salty flavor,” so I’m watching for the fruits to ripen enough for a taste. When fully ripe, the tomatoes are a dark reddish purple or brown (not truly black) and with dark green around the top, or shoulder.

Screen Shot 2015-07-30 at 11.57.09 AM

Black Krim Tomato Credit: www.gardenharvestsupply.com/

Another priority for the summer is mulching, which is actually a good practice for any season, whenever the soil is uncovered. Mulching discourages weeds, slows the evaporation of moisture, creates a good environment for soil microbes, and protects the soil from erosion.

Organic mulches are available in garden centers in bags of 1.5 or 2 cubic feet. For larger gardens, chipped material from a tree service is a low-cost alternative. Such material is coarser than commercial mulches, and consequently lasts longer.

A tree service will drop a load of chips on your property without charge, if you can receive it on their schedule. Another option is load a yard or two of chips into your truck, at the service’s premises. Call ahead!

A responsible tree service will not bring or offer chips from diseased trees, but otherwise the chips will be from a randomly chosen pruning project. All chips are good in the garden, but some are more aromatic than others. Think eucalyptus!

Finally, during these warm summer months, we can anticipate significant rainfalls this winter, based on the meteorologists’ assessments of the El Niño ocean conditions. Potentially heavy rains won’t completely end our drought, but it could help a lot.

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Gardening’s Underlying Science

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We appreciate our gardens for their beauty and natural vigor, even as we know, deep down, that each plant is a wonder of science.

Well, perhaps that thought hasn’t entered your thoughts, recently, but it’s still true.

You might think we don’t need to dig into the science behind plant growth, as long as we keep them fertilized and watered and they keep growing. That’s not necessarily true!

I’ve been gaining interesting information about the science that underlies garden plants. One of the very good sources of that information is horticulturist Linda Chalker-Scott, Ph.D. She has published fine research reports, taught a lot of university courses, and has communicated a lot of plant science to home gardeners through Master Gardener programs in the State of Washington and her writing.

Her writing for lay readers has been published in several books and periodicals, and on The Garden Professors, a blog on which she and several colleagues share their expertise and opinions. This website (http://gardenprofessors.com/) includes fascinating reports of gardening myths.

Misconceptions abound in the gardening community.

I first became aware of Chalker-Scott’s contributions through two of her books, The Informed Gardener (2008) and The Informed Gardener Blooms Again (2010).

Her newest book is How Plants Work: The Science Behind the Amazing Things Plants Do (Timber press, 2015).

The Informed Gardener

In How Plants Work, she presents basic concepts of plant biology: cells, roots, nutrition, photosynthesis, leaves, seasonal cycles, growth patterns, pruning and propagation. (This very brief list of the book’s topics doesn’t convey the depth of her presentations. See the book for the full information.)

Dr. Chalker-Scott has written these chapters with her well-established commitment to communicating her scientific knowledge to non-scientific readers. She has managed to present the science effectively without “dumbing it down.” Gardeners with limited backgrounds in biological science can understand and appreciate this information, but will have to stay focused and perhaps read some passages more than once. I certainly did!

The book addresses some gardening myths, which I find always interesting, but emphasizes the positive message: knowing “how plants work” is the foundation of successful gardening.

To encourage you to read this book, I will share one of the book’s gardening myths, and an example of its garden science nuggets about which gardeners should know.

Myth: Landscape fabric blocks weeds while letting water and oxygen to pass through.

Reality: These fabrics soon become clogged with soil particles, and block the movement of water and oxygen. Meanwhile, weeds become established on top of the fabric, and some aggressive varieties manage to poke through.

Science Nugget: All plants have primary compounds that are required for growth and development: sugars, DNA, fats and proteins. They also produce secondary compounds that defend against pests and diseases, or that attract pollinators, or have other properties that are currently unknown. Chalker-Scott describes several kinds of secondary compounds and reports that every plant produces one or more unique compounds, and that scientists know about less than ten percent of the compounds that plants make.

We think we know a lot about the plants in our gardens, but we have a long way to go.

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Restoring Soil

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Several people commented on last week’s column on the carbon cycle. All endorsed the concept of restoring garden soil, to support its natural ability to sequester carbon.

One reader had questions about how to go about restoring garden soil. This is a Big Topic and you, good reader, might have your own questions, but you also might share his interests. My brief responses are below. Visit gardening.com for more details, including plant suggestions.

Q. Plow the grass under?

A. Losing the thirsty lawn is a good first step, because such monocultures are not appealing to wildlife. Plowing, however, could both promote re-growth of the grass and bring dormant weed seeds to the surface. A better approach is to kill the grass over several sunny weeks by covering it with clear plastic (solarization), or with newspaper or cardboard (smothering).

For information on Soil Solarization for Gardens & Landscapes, visit the University of California’s Integrated Pest Management webpage on the topic. The presentation emphasizes pest control; in this context, unwanted turf grass amounts to a pest.

The California Native Plant Society has Detailed lawn removal advice.

Q. Plant different grass?

A. Yes! California native grasses can provide the basis of an attractive meadow, which is more casual than a manicured carpet of turf grass. A meadow has unique aesthetic appeal; supports a variety of wildflowers and wildlife; requires little water, infrequent mowing, and no chemicals; and helps to restore the soil.

Kids on Native Grass Lawn
JACQUELINE RAMSEYER —
BAY AREA NEWS GROUP

Lily Baker’s front yard in San Jose
features a native grass lawn.
California native grasses help restore the soil.

For information on several California native grasses, visit the Tree of Life Nursery’s web page, “Masses of Grasses.”

A very good book by Carol Bornstein, David Fross, and Bart O’Brien is Reimagining the California Lawn: Water-conserving Plants, Practices, and Designs (2011).

Q. Grow more trees?

A. Absolutely! Trees and large shrubs are attractive additions to the landscape, valuable participants in the carbon cycle, and welcomed by all forms of wildlife. Invest a little research to select trees will thrive in your climate, and grow to an appropriate size for your landscape. Again, California natives are good choices.

A good introduction to California native trees and larger shrubs is available from the non-profit Nipomo Native Garden, which has produced a web page, “Native Trees for Landscaping and Wildlife.”

Q. Eliminate ground cover in favor of something with deeper roots?

A. Ground covers are any plants that hug surface or rise to any height up to four feet. Most importantly, they protect soil and soil microbiota from baking in the sun, or eroding. During the fall and winter, plant seasonal cover crops that draw nitrogen from the air and store it in their roots. Examples of such “nitrogen-fixing” plants include peas, beans, and clover. In the spring, before your cover crop sets seed, till the plants under to decompose and release their nitrogen into the soil to support the growth of other plants.

Deeper roots mean better drought-tolerance: deep-rooted plant can find moisture far below the surface. Such plants are generally preferable in the landscape, all other factors being equal.

The depth of roots varies among plants, reflecting adaptation to the plant’s environment. Among weedy grasses, for example, Annual Bluegrass (Poa annua) has roots only about right inches deep, while Bermudagrass (Cynodon dactylon) can grow to 60 inches deep in search of water.

Infrequent, deep irrigation encourages all plants to develop deep roots and drought tolerance. A common error with automatic irrigation systems is to schedule frequent, brief periods of watering. This practice encourages shallow roots, ultimately increases overall water usage and leaves plants vulnerable to dry periods.

Q. Shallower roots?

A. The advantage of shallower roots is that plants growing in arid climates have immediate access to occasional rains. Succulent plants have adapted to such conditions by developing shallow roots and the ability to store scarce moisture in their leaves, stems or roots. For this reason, gardeners often appreciate succulent plants for both drought tolerance and landscape appeal.

The New California Garden, which we envision here, features meadow grasses and succulent plants: a good time to start is now.

Gardening to Reverse Climate Change

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The threat of climate change has become a concern among scientists, environmentalists and gardeners (who might wear all three of these hats, of course). In the search for solution to this problem, these three interested parties have common ground, as we explore in this column.

As background, our climate is changing as a result of a disruption of the Carbon Cycle.

On Plant Earth, a fixed amount of carbon cycles through different forms: liquid, solid, or gas.

Carbon enters the atmosphere from several sources, including respiration of animals and plants, decay of animals and plants, eruptions of volcanoes, and releases of dissolved carbon dioxide (CO2) from the oceans.

Plants absorb carbon dioxide (CO2) from the atmosphere, and use photosynthesis to release oxygen back into the atmosphere and convert carbon into sugars that support the plant’s above-ground growth. At the same time, up to 40% of the CO2 goes to the plant’s roots, to feed soil microbes. The microbes assist the plant to acquire nutrients through its roots, and lock (“sequester”) carbon into the soil for very long periods.

The Carbon Cycle supports Earth’s climate and enables the growth of plants and literally all other living things.

Carbon Cycle

Credit: NASA/Globe Project

In the diagram above, notations in blue indicate pools of carbon and notations in red indicate fluxes of carbon, both quantities are measured in petagrams.

This complex natural process balances the amount of carbon in liquid, solid and gas forms. Vast amounts of carbon are stored in the soil and fossil fuels, and much smaller amounts are stored in the atmosphere, the oceans, and plants.

During the Industrial Revolution (1760 to c. 1830), humans began burning fossil fuels, cutting down forests, draining wetlands, converting grasslands to large-scale crops, paving paradise, and applying synthetic chemical fertilizers and pesticides. These activities have been disrupting the Carbon Cycle and altering this important balance.

The consequences include degraded soil with reduced ability to capture carbon, an excess of carbon in the atmosphere, the acidification of the oceans, and other effects, none of which are beneficial to living things (including us).

The broad term, climate change, encompasses all these negative effects.

Restoring the natural Carbon Cycle could reverse climate change.

Restoration requires feeding the soil with organic matter and planting cover crops to protect the soil from temperature extremes and erosion. In short, the solution is based upon regenerative, organic agriculture.

This strategy must be employed on a global scale, but we all should understand the Carbon Cycle and support this process of soil restoration in our own gardens and in our individual contributions to relevant public policy. Substantial private interests are invested in fossil fuels, “conventional” monoculture agriculture that depends upon synthetic chemicals, and other industrial methods that are changing our climate. They can be expected to resist this strategy of working with nature, so eventual success requires our vision and long-term commitment.

Each gardener could participate first in his or her own garden. That would be a fine way to celebrate our independence from, in this context, commercial interests.

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