l Double dig, a British expression, is what avid gardeners do. It refers to loosening the soil by turning it eight to 10 inches deep on the first tilling and then another eight to 10 inches deep in a second tilling to create a total depth of 16 to 20 inches of loose, friable soil.
reen roof is a roof with a garden or parklike area. For years, green roofs have been used as shelter from the weather. For example, there are sod roofs that have been used in different parts of the country or roofs made of drought-tolerant plants. But green roofs have become more extravagant. Many are found on commercial properties, and they can be used for strolling and might include a shelter for protection. They’re increasingly designed to be aesthetically pleasing. The Mormon Temple in Salt Lake City has one of the grandest rooftop gardens I have seen, with planters, prairies, forests, shrubs, deciduous and coniferous trees, and water flowing across the garden and over the edge of the building. If you want to learn more about green roofs, take a look at “Green Roof — A Case Study: Michael Valkenburgh Associates’ Design for the American Society of Landscape Architects” by Christian Werthmann.
l Genetically modified seeds are those that have had their cells biologically engineered to resist pesticides and keep their seeds from germinating (making many of them sterile).
l Invasive alien plants, such as amur honeysuckle, are flora that are native to Asia and Western Europe but have colonized in many parts of this country, eradicating the habitats of native plants that wildlife need for shelter and nesting.
l Cultivaris a term used to describe a plant that is cultivated to introduce characteristics that set it apart from other plants in the same species. The cultivar name is set off by single apostrophes at the end of the botanical name and is sometimes used as a common name for the plant as well. For example, fringed bleeding heart (Dicentra
eximia) is a beautiful specimen for your garden. The cultivar (Dicentra
eximia ‘Luxuriant’) has a more graceful habit, and its 15-inch-long stems flower red when planted in a predominantly shady, moist, well-drained site rich in compost. Cultivars are not grown from seeds; they are grown from rooted cuttings taken from the parent plant to ensure that the offspring will have the same characteristics.
l Living walls are green spaces on the walls of houses or commercial buildings. These walls can have plants that grow vertically up steel structures or plants that use their tendrils or aerial roots to attach themselves to walls. Plants can also cascade down a wall from planters.
l Native plants can be a confusing term. Are the plants native to certain regions of the country or all of North America? Native plant purists consider native plants to be those that grow in a specific microclimate. Purists would say that purple coneflowers are native to Colorado, where they originated, even though they have been transplanted all over the East Coast.
l Rain gardens retain storm water and use it to infiltrate the ground, filtering pollutants and recharging the ground water. “Ideally, most, if not all, of the water that falls on a site should stay on the site,” says Zora Lathan, executive director of the Chesapeake Ecology Center in Annapolis.
l Runoff refers to storm water washing oils, salts, trash and sediment into streams and rivers. It is responsible for excess nitrogen that stimulates the growth of algae, which cuts light and oxygen to other aquatic life.
l Permaculture describes the philosophy for creating healthy communities. Toby Hemenway, author of “Gaia’s Garden: A Guide to Home-Scale Permaculture,” says permaculture aims to build ecologically sound, economically prosperous communities for people, wildlife and plants to coexist in harmony. One way of doing that is to minimize imports and exports from a site, including fuel, fertilizer and soil amendments. Permaculture relies on existing energy flows for sun, wind and water power, according to “Living Community: A Permaculture Case Study at Sol y Sombra” by Ben Haggard. Another precept of permaculture is to create compost to enrich the soil and use gray water to irrigate plants. As it flows through the vegetation to a lower part of the garden, the water is purified into potable liquid and can be used again.
Joel M. Lerner is president of Environmental Design in Capitol View Park, Md.