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Water-wise hydrozones

  • April 4, 2020
  • Barbara Robertson
  • Is it déjà vu all over again? Will gardeners add “drought” to the growing list of things we need to think about this year? As I write this column, I’m hoping for the “March Rain Miracle” because the Marin Municipal Water Department reports rainfall at Lake Lagunitas is less than half a year ago, and only 67 percent of normal. 

    So, this is a timely reminder that when planning a new garden, replanting a few plants, or remodeling an existing garden, do it with water needs in mind as a good practice. Moreover, it turns out that creating a water-wise garden fits nicely within fire-smart and climate-smart landscaping practices. 

    You can improve the efficiency of watering and avoid under watering or over watering, which leads to runoff, by creating hydrozones. Hydrozones are groupings of plants with similar water needs. Fire-smart landscaping advisors suggest grouping plants into ‘islands” with hardscape interspersed as a fire break and for ease of maintenance. Each island could be a hydrozone and thus be water-wise, as well. 

    You might, for example, plant a well-watered edibles bed in the fire-smart zone five to 10 feet from your house. Growing your own food is climate-smart, and if you place that edibles grouping within fire-safe proximity to your home, it saves your own energy going back and forth to harvest.  You could then place an island of water-wise native pollinators farther away. Thoughtfully planned islands can help not only provide the spacing desired for fire safety, they make thoughtfully designed irrigation by hydrozones easier to design and install. (Check http://marinmg.ucanr.edu for see Fire-smart Landscaping practices on our main page and follow local policies.)

    But, how do you know how much water plants need?

    A remarkable online tool called WUCOLS IV – Water Use Classification of Landscape Species – can help (https://ucanr.edu/sites/WUCOLS/). Based on observations and extensive field experience of 36 landscape horticulturists, WUCOLS IV provides the irrigation water needs of over 3,500 taxonomic ornamental plant groups used in California landscapes. 

    That makes it useful for planning new gardens, to check the actual water needs for plants on existing irrigation lines, and to know which plants to add on a line. You may discover you can reduce water usage in already planted areas.

    You can search the WUCOLS database by city and/or plant name (Latin or common), and select plants based on water use and/or by type of plant. 

    The result is a list of plants meeting your criteria, many with pictures. All have descriptions that include size, appearance, requirements, and sometimes a bit of history. As you select plants, you can collect them into a list. 

    For example, I searched WUCOLS for Mill Valley and Ceanothus and saw a list of 49 plants. I scanned the photos and discovered Ceanothus gloriosus (‘Anchor Bay’), a ground cover growing up to three feet tall by eight feet wide with dense holly-like leaves on spreading branches and clusters of blue-violet flowers in spring. The native of San Luis Obispo County coastal bluffs likes cool sun and afternoon shade inland. It has low water requirements, but prefers moist well-drained soil.  A search for rose hybrids returned an expected “moderate water” need, but the roses ‘Cecile Brunner’ and ‘Rosa Rugosa’ (Japanese Rose) need only low water.

    Using WUCOLS to think smarter about how to make my existing garden better suited to our changing climate became a wonderful way to spend a shelter-in-place afternoon. 

    Artists often talk about how restrictions can foster creativity. The same can be true in the garden. UC Marin Master Gardeners often promote the idea “The right plant in the right place.” With water-wise, fire-smart, and climate-smart considerations to keep in mind, it could be time to think about the inverse as well: Creating the right place for the right plants.