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Elisabeth C. Miller Library

Keyword: Water conservation

Gardening in Summer-Dry Climates: Plants for a Lush, Water-Conscious Landscape

Gardeners are quick to discover that the Seattle area, and most of the coastal areas of the Pacific Northwest, tend to be dry in the summer and wet in the winter, despite our collective rainy reputation.  Many popular gardening books are from regions with reliable summer rains.  The plant palette these books suggest don’t work here without lots of supplemental water.

For decades, the encyclopedic “Sunset Western Garden” books have provided local guidance, especially with their fine-tuned zones that not only consider the impact of winter cold, but also summer heat, rainfall patterns, and topography.  While the last of these “Sunset” encyclopedias was published in 2012, these zones are now applied in a new book, “Gardening in Summer-Dry Climates” by Nora Harlow and Saxon Holt.  The authors also provide the “California’s Water Use Classification of Landscape Species” (WUCOLS) ratings, a handy tool that is useful even in Washington for estimating the water needs of a specific plant.

Both authors are from northern California, but they have done their research on the needs of gardeners further north, making this book useful well into southwestern British Columbia.  They recognize that “gardeners up and down the Pacific coast also share an upbeat conviction that the way we garden can make a difference.”  This can be achieved in different ways, but a primary tenant is “to work with rather than fight the summer-dry climate.”

The heart of this book is an alphabetical listing of plants chosen not only from the authors’ knowledge, but also the recommendations of an impressive list of regional experts.  To me, it feels a bit biased to northern California selections, but this is how the Sunset zones are handy.  Knowing that around Seattle you are either in Sunset zone 5 (near the water) or 4 (nearer the foothills), you can make sure the plant will grow for you.  The plant selection includes a mixture of trees, shrubs, perennials, annuals, and ferns, many of them natives to the region.

The rich photographs by Holt make this book an especially enjoyable but these images are also well-crafted to give a clear sense of growth habits.  Introductory essays and appendices further help with selection of plants, and how to address the special design considerations such as climate trends and the increasing dangers of wildfires.  If you’re designing a new garden, or revamping an old, this is an excellent resource to consult.

Excerpted from the Spring 2022 issue of the Arboretum Bulletin

Seattle Public Utility’s Thornton Creek Watershed Characterization Report

“This Thornton Creek Watershed Characterization Report presents background information about the Thornton Creek watershed. It is the first step in developing a Watershed Action Plan that will guide actions by government agencies, citizens and businesses to: reduce non-point source pollution; protect biological resources; preserve, enhance and restore fish and wildlife habitat.”

harvesting rooftop runoff water for vegetable gardens

I need to replace my roof, and I am thinking of installing asphalt or composite shingles because they’re what I can afford. I planned to capture rain water to irrigate my vegetable garden, but I’m concerned about toxicity. Is runoff from the shingled roof likely to be toxic?

 

I would not recommend using reclaimed rainwater from an asphalt shingle roof for any edible crop. Asphalt is petroleum-based. The runoff might be acceptable for ornamental plants, but the fact that asphalt or composite shingles tend to shed tiny particles means that those particles would be introduced to the soil around your crops.

An article from North Carolina State University Extension discusses “Water Quality of Rooftop Runoff.” It doesn’t specifically mention asphalt, but I don’t think it would be wise to use the reclaimed water on food crops.

Green Living Journal (now archived) has an article about roofing materials, and discusses asphalt shingles as well as alternatives.

The National Gardening Association site has a report, no longer available online, that describes rainwater harvesting.
Excerpt:
“Water from the rain barrel is, of course, not potable, but some experts also raise concern about possible contaminants from rooftops that can make the water unsuitable for edible gardens. According to an article in Landscape Architecture magazine, asphalt shingles and other porous or rough roofing materials can hold particulates such as bird droppings and other debris, as well as heavy metals from the air, which then wash into the rain barrel. Wood shingles that are chemically treated to resist rot and algae can leach the chemicals into the rainwater running off the roof. Zinc strips that prevent moss build-up can also be problematic. Some large-scale rainwater collection systems are even designed to allow for the first flush of water off the roof — which carries the majority of the questionable substances — to be diverted.

“Other people dispute these risks and say washing your garden produce is all that’s needed. It’s a judgment call. I tend to research things to death so I think it would be interesting to have some of my rooftop runoff tested at the health department.”

There is a very detailed and technical document entitled “Roofing Materials Assessment” from Washington State Department of Ecology (2013-2014 study results) if you wish to pursue the topic further.

If installing slate, clay tiles, untreated wood shingles, or a green roof is prohibitively expensive, the best solution might be to landscape the garden in such a way that you can reclaim runoff from the roof for non-edible plants.