Climate Zones 101

Sandy soils, dry winters—we're not in Palo Alto any more!

This week I was down at the San Diego Botanic Garden, where the differences between the Encinitas climate and the Palo Alto one I live in were on full display. For landscape designers like me who grew up reading the Sunset Western Garden Book, the concept of climate zones is second nature. But for plenty of other folks, it's about as foreign as, well, another land.

Horticulturally speaking, a climate zone is simply an area where the growing conditions are consistently unique from any other area. Back in 1960, the U.S. Department of Agriculture defined 10 "plant hardiness zones" throughout the country, based mainly on winter low temperatures to help growers understand where crops would, and would not, survive the winter. Over time those definitions have been refined and the zones subdivided, and today there are 26 USDA zones. You can see a map online here.

Here in the West, Sunset Magazine took the idea a step further, defining "Sunset climate zones" that take into account not only winter low temperatures but also summer highs, wind, rainfall, humidity, elevation, latitude and ocean influence. The result is a finely detailed picture of where plants will not only survive, but thrive. From its original 13 zones in the western states, Sunset now has identified more than 50 unique climate zones throughout the U.S. and Canada. These climate maps have become indispensable tools for garden designers, landscape architects, builders, and of course homeowners. Plant growers, who want gardeners to have success with their products, routinely label their plants with the USDA and/or Sunset zones those plants are best suited to.

But why do zones matter, anyway? Because — whether for a budding home gardeners or a professional landscape architect — the first rule of planting design is "right plant, right place." So if you're designing a garden in San Diego, you can know that here in Sunset Zone 24, winters just won't get cold enough for most cherry trees to bear fruit. On the other hand, if you're designing for Palo Alto, you can assume that the Agave attenuata that thrives down here in the mild coastal desert will turn to mush during our freezing Zone 15 winters.

Subtropical trees thrive in a subtropical climate zone

Sure, plenty of people are in what I call "zonal denial" — gardening on the edge of reality, insistently planting frost-tender plants in cold-winter areas (and high-water turf grass in what's really a desert). They may skirt outright failure enough to be emboldened in their efforts, but their gardens aren't really thriving. And plants draped with flannel sheets and holiday lights probably aren't the curb appeal most people want.

So don't live in that state called denial. Know your zone and plant accordingly. Your garden, and your neighbors, will thank you!

Agave 'Blue Flame', hardy to 25°F — just on the edge of Palo Alto's climate

California's New(ish) Irrigation Laws

Although California has legislated landscape irrigation for a few years now, most of us haven't noticed it… until now.

But suddenly, homeowners applying for construction permits are getting the unpleasant surprise that a whole package of landscape documentation, including irrigation and planting plans and a slew of math, may be required as part of the permit submittal. What the…?!?

A brief history: way back in 1990 the state determined (wisely) that water is a finite and precious resource in this Mediterranean climate, and 16 years later managed to enact Assembly Bill 1881 to promote the conservation of water in the man-made landscape. (A much better history is here.)

As part of AB 1881, California drafted a Model Water Efficient Landscape Ordinance (MWELO), which defines maximum applied-water allowances and requires estimates of total landscape water usage based on calculations of plants' evapotranspiration rates and a few other factors. If that sounds complicated, it is; and a cottage industry of designers and auditors versed in not only horticulture but also irrigation principles and documentation has grown in response.

AB 1881 also mandated that by 2010, local governments adopt either the state's Model Ordinance, or a local landscape ordinance that is at least as effective as the state's in conserving water. Now, most local governments are not known for either their foresight or their ability to respond nimbly to a bureaucratic requirement. So, unsurprisingly, in 2010 quite a few cities opted to simply adopt the state's ordinance as-is; and because enforcement would require staff which would require money and perhaps cost (or at least delay) permit revenue, most were less than stringent in enforcing the new law.

The tide has turned, however, and now towns from Agoura Hills to Yucaipa have adopted local ordinances, and figured out how to enforce the requirements within their zoning permit process. As a result, many more garden designers and landscape architects have become conversant in acronyms like MAWA, ETWU, WUCOLS, ETAF, and ETo, and begun offering landscape documentation packages as part of our services. It's a lot of work — here's the MWELO submittal requirement:

§ 492.3  Elements of the Landscape Documentation Package.
(a) The Landscape Documentation Package shall include the following six (6) elements:
(1) project information;
(A) date
(B) project applicant
(C) project address (if available, parcel and/or lot number(s))
(D) total landscape area (square feet)
(E) project type (e.g., new, rehabilitated, public, private, cemetery, homeowner-installed)
(F) water supply type (e.g., potable, recycled, well) and identify the local retail water purveyor if the
applicant is not served by a private well
(G) checklist of all documents in Landscape Documentation Package
(H) project contacts to include contact information for the project applicant and property owner
(I) applicant signature and date with statement, “I agree to comply with the requirements of the water
efficient landscape ordinance and submit a complete Landscape Documentation Package”.
(2) Water Efficient Landscape Worksheet;
(A) hydrozone information table
(B) water budget calculations
1. Maximum Applied Water Allowance (MAWA)
2. Estimated Total Water Use (ETWU)
(3) soil management report;
(4) landscape design plan;
(5) irrigation design plan; and
(6) grading design plan. 

Additionally, the Landscape Documentation Package is usually required to be signed by a licensed landscape architect, licensed landscape contractor, or certified irrigation auditor. Which means that in addition to being a lot of work, it's not cheap.

Fortunately, WELO requirements do not apply to every project. If a permit isn't required, for instance, or if the total affected landscape area is less than 5,000 square feet, the state MWELO wouldn't apply. But since most cities have their own ordinances now, the only way to know for sure is to call your local building department and ask for a copy of the local WELO.

There are a couple of pieces of good news in all this. First, if you're clear on your WELO requirements at the outset of your construction project (i.e. at the beginning of design, not the day before you plan to submit your plans), there's no reason a qualified professional can't prepare your documentation well in time for permitting.

Second, the fact is that WELO requirements—although a bureaucratic tar pit—are saving water. They are forcing all of us to reconsider gratuitous lawns, to learn our water-thrifty plants, and to group those plants into sensible hydrozones, which is just good horticultural practice. As landowners and designers and stewards of the earth, we all are getting a little bit better in our roles.

Imagine that.

What Are We Doing Here?

The artful landscape holds surprises big and small.

I'm really not one to make new years' resolutions, but as I head into my tenth year of designing landscapes, I know there is an opportunity here to do a lot more than simply decorate people's yards.

Water management is something we all need to be thinking about, whether it's controlling winter flooding or surviving summer drought. The last ten years have seen a remarkable increase in awareness of permeable landscaping as well. From interlocking paver systems to poured-in-place pervious concrete, products are available now that will lower the impact of our development in almost any application. There also has been a vast increase in the number and diversity of native and adapted plant species available, as nurseries realize "low water" and "low maintenance" are more than just a trend.

These are all strategies to make the earth happier, and that's important. But it's also important to keep the spirit happy. The landscape isn't just a place we happen to walk through; it's where we live. It's what we come home to, where we relax, where we entertain our family and friends and the people who aren't yet friends but will be soon. The landscape not only inspires us, but also invites to to take part in its beauty, and by extension, the beauty of the surrounding environment: our world.

When we are sensitive to our landscape, we notice the little things: the morning frost, the autumn foliage, the summer sunset. We notice the long winter shadows, and appreciate the long summer days that much more. And, even as we become attuned to the regularity of the days and the seasons, we are also more open to the surprises that await us everywhere we take the time to look (or smell or listen or touch or taste). And this, this brings us joy.

I coined the name "Verdance" to convey what I hoped to offer every client: the artful combination of "green" (verde) with "joy" (danz, or dance). That's still what I'm doing here, and I've been lucky enough over the past ten years to work with a few clients who want to do it together.

Who's next?