Rainscape Design

Using Native Plants to Clean Up Toxic Sites

Ira Johnson — Sun, 12 Jun 2011 21:35:01 +0000

There are several kinds of bioprocesses that use plants to clean up soil toxins (Phytoremediation), but a couple stand out as being more valuable to use by landscape architects and garden designers. Phytostabilization (the immobilization of contaminants by plants) and Rhizosphere Biodegradation (the breakdown of soil toxins by microbes in the soil level called the rhizosphere) are the most applicable for broad use primarily because they are less expensive than other kinds of phytoremediation processes. However, there are other benefits in using these two processes over some of the others, the most important being the link between site cleanup and habitat restoration when native plants are used instead of non-natives.

When phytostabilization is applied soil toxins are ‘locked up’ or stabilized in soil, limiting the spread of the toxic pollutants to other areas. These mechanical and chemical processes can be further enhanced with a well-designed planting plan that creates an extensive and elaborate rhizosphere that can host a variety of toxin destroying microbes. Native plants are most suitable for doing this due to the extensive root systems they have evolved over time to deal with periodic drought conditions. Native plants have also co-evolved with numerous local soil microbes, giving them an advantage over exotic non-natives in creating extensive microbial communities in the rhizosphere. What’s particularly good about combining phytostabilization and rhizosphere biodegradation is that you can use native plants to accomplish both processes. These bioprocesses can be applied to any region of the country by utilizing the local flora and fauna, and in this case the local fauna includes local soil microbes.

Rainscape Design’s native planting plans can be applied in phytostabilization and rhizosphere biodegradation schemes. Our specifications for installation and maintenance of these remediation landscapes are intended to help establish transplants quickly, with beneficial microbes, and create a sustainable nutrient cycle. This nutrient cycle also supports the microbes needed to neutralize toxins in the soil. For more on using native plants for phytoremediation see the following link: Spiraling Roots.

Planting with Bay Area Rain Patterns

Ira Johnson — Wed, 16 Feb 2011 02:58:27 +0000

The San Francisco Bay Area’s rainfall pattern and quantities vary widely from one year to the next and from month to month. See Weather Link for details. This creates some opportunities and challenges to gardeners and the landscape industry. In this region, regardless of your micro-climate conditions, it is possible to plant, grow and enjoy a variety of food crops and ornamental plants, year round. A simultaneous opportunity and challenge is timing when you plant something to take advantage of the rain softening effect on soil to make the job easier, without taking the risk of working soil that’s too wet.

Due to the clay content of many soils in the region, a challenge for the landscape industry (and the home gardener) is constructing landscapes and installing planting plans without damaging soil structure. All soils, except sandy structured ones, are susceptible to soil compaction while wet and even dry soil can be affected. It’s the clay soils, however, that risk the chance of being permanently damaged structurally, if worked while too wet. In this case, degree matters. Clay soil needs to be moist to be workable at all (especially with hand tools), but if too wet, even walking on clay soil can severely compact it. This often leads to nutrient-rich, clay soil being hauled away and replaced with sterile imported soil, adding cost to a project and creating less sustainable plantings in the long run.

This winter’s early and significant rains have made the last four weeks or so, an ideal time to “work the soil.” It’s been moist, but not too wet. There are things you can do to protect soil as you take advantage of this time. Mulching with a thick layer of wood chips is protective to soil, as is temporarily laying down plywood or other broad expanses of stiff material to walk on adjacent to the areas you are working. This disperses your body weight, lessening the risk of compaction. Our rain pattern is predicted to change over the next week. Working with the pattern, instead of against it has lasting (sustainable) benefits.

Five reasons to have your landscape professionally designed by a landscape architect

Ira Johnson — Tue, 04 Jan 2011 19:27:02 +0000

Professional design of your landscape:

Expands your home into the outdoors where you can enjoy California’s climate year round.
Allows you to direct resources to where they are most needed, saving you time and money.
Allows you to distribute your water resources to what is most important to you and your family, saving you money.
Allows you to phase in installation according to your budget.
Design fees are usually less than 20% of the overall cost of a project.

Visit our services page for a complete list of our landscape design and construction capabilities.

Leaving plant litter in place

Ira Johnson — Wed, 29 Dec 2010 17:34:28 +0000

The common landscaping practice of mulching under and around plant material to conserve water, help maintain consistent substrate temperatures, and as a weed inhibitor, can also play a role in carbon sequestering and global warming. Of the variety of mulches used in landscape maintenance, the most important and least used is litter from the landscape itself. The biomass generated by trees, shrubs, perennials, and ground covers (high in Carbon content) is typically blown off and hauled away, adding unnecessary expense to usually tight maintenance budgets. If the collected plant litter is placed in landfill sites, then the 45%-50% of carbon contained in the material is slowly converted to methane gas (Smith and Heath). Methane gas is 23 times more potent than CO2 as a greenhouse gas (Keppler and Rockmann 54). Alternatively, if plant litter is left in place then the carbon it contains is sequestered for extensive periods of time while the material decomposes and is absorbed by the soil (Hu). In addition, while covering the soil surface, plant litter slows down emissions of CO2 from the soil to the atmosphere (Si-Qing et al).

We recommend in our maintenance specifications to leave all but large, hazardous, and unsightly plant litter in place to help establish a sustainable nutrient cycle.

Sources

Keppler, F. and Rockmann, T. 2007. Methane Plants and Climate Change. Scientific American, February.

Hu, Shuijin 2001. Nitrogen limitation of microbial decomposition in a grassland under elevated CO2. Nature, January/409. 188–191.

Si-Qing, C., Xiao-Yong, C., Guang-Sheng, Z., and Ling-Hao, L. Study on the CO2 release rate of soil respiration and litter decomposition in Stipa grandis Steppe in Xilin River Basin, Inner Mongolia. Journal of Integrative Plant Biology.