July 13th, 2009



California Poppy Reserve March 2009

 When excavation is required, take care to preserve existing top soils, to set them aside in the order in which they were removed. Value and protect site soils during the construction process and return them to the land as close to their original place as possible when construction allows. Cover site soils with organic mulch during the construction process to a depth of at least 6 inches to prevent the intrusion of invasive species. Keep the soils cool and encourage microbial activity.


Landscape with native plants, particularly plants selected from the plant communities of the region.  When soils are protected and allowed to return to their native state, we are designing for the protection of the natural world. Healthy native soil is a sponge. It absorbs rain and slows down run-off. It stores and releases water and nutrients as plants require them. It filters, traps and ultimately breaks down urban pollutants such as oil, metal and pesticides. It also filters and purifies the air and water that percolate through it. It perpetuates life on the Earth by supplying valuable nutrients and antioxidants to plants.


Disturbed soils invite invasive plant species to thrive. Invasive plants affect water quality, species diversity and populations, reduce favorability for species reproduction, and reduce available food sources. Invasive plants accelerate soil erosion and stream sedimentation, absorb precious water sources and affect water quality.



Disturbed site

 When an exotic plant invades a soil community, it can alter the links between the plants and organisms that are above the ground and the plant parts and organisms that are below the ground.


A billion soil microbes are found in one teaspoon of soil. Perhaps of those billion soil microbes, there are 4000 different species of bacteria, fungi, nematodes and protozoa. The bacteria bind the finer soil particles together. These become micro-aggregates bound together by fungal vegetative growth. The abundant presence of these symbiotic fungi leads to substantial increases in the nutrient uptake of host plants. Because mycorrhizal fungi can have affects on both individual plants and plant communities, when an invasive plant is able to alter their dynamic, this may affect the long-term relationships of many plant species in a forest.


Exotic plants can directly alter the physical properties of the soil and the attributes of an ecosystem. Certain invasive plant species literally transform ecological communities.



Chaparral garden with a gravel driveway



Grassland and chaparral garden

If we hope to create truly sustainable communities, understanding and protecting local ecosystems for future generations can only be accomplished when we restore our native soils by selecting plants that have evolved in those soils for millions of years.  If you’d like to view the article in its entirety, please click on www.middlebrook-gardens.com


is a committed advocate and practitioner of the sustainable lifestyle, respected landscape professional and California native plant specialist. Her San Jose, California-based build/design firm, Middlebrook Gardens, has installed over 250 California native gardens and remains on the leading edge of the rising sustainability movement.


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