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Specializing in colorful, water-conserving gardens

Specializing in colorful, water-conserving gardens

Summer Reading: Bob Perry’s Landscape Plants for California Gardens


When is a picture book more than a picture book?

When it’s Bob Perry’s “Landscape Plants for California Gardens.”

The new, encyclopedic book features 3,100 color photos, along with detailed descriptions and growing tips for 2,100 plants. Perry includes the usual suspects, such as roses, lantana and agapanthus, along with scores of interesting natives and other Mediterranean plants.

What’s more — and what truly sets this book apart — is the extent to which Perry identifies the irrigation needs of those 2,100 plants.

“I wanted to produce a resource that could be useful for many garden and landscape situations, while at the same time continuing to advocate the need to conserve water,” Perry said.

Orchid rockrose

Indeed, whether you’re installing a new landscape, adding a few plants or just applying the information to your existing garden, Perry provides exactly what you need to know, including methodically systematizing the seasonal watering requirements of each and every plant.

Altogether, the color photos and detailed information make the book far more comprehensive than any other California gardening book I’ve read, including the venerable Sunset Western Garden Book. Thanks to all those glossy photos, it also weighs in at nearly 8 pounds. It will be the mainstay of my garden library for years to come.

A Few Easy Steps

Now plenty of writers and gardeners — myself included — emphasize that many California natives and Mediterranean plants are ideally suited to grow here on the Central Coast because they’re naturally adapted to our moist, cool winters and dry, warm summers.

But Perry is the first author to organize such a broad spectrum of landscape plants into a deceptively simple system.

First, he sets out two irrigation groups.

Group 1 plants, such as Japanese maples, hibiscus and roses, need to be watered on a regular basis all year.

Group 2 plants, such as many succulents and native plants, grow well with dryer conditions during summer.

“That was done with the specific intent to bring attention to plants that are California natives and Mediterranean and arid climate adaptations that would thrive with regular to normal winter rainfall in winter months, and would perform well and look good with reduced amounts of supplemental water in summer months,” Perry said. “And not just simply ratchet up the irrigation for all plants during the summer months when turf grass needs the most supplemental moisture.”

Within those two irrigation groups, Perry assigns “plant factors,” which describe each plant’s year-round watering needs.

Group 1 plants need consistently high (H), moderate (M) or low (L) irrigation throughout the year.

Group 2 plants need high/moderate (H/M), moderate/low (M/L) or low/very low (L/VL) irrigation, depending on the season.

Otto Quast Spanish lavender

For instance, Perry lists ivy geranium (Pelargonium peltatum) as M – 1, which means it needs moderate irrigation year-round, while Spanish lavender (Lavandula stoechas) is M/L – 2, which means it grows well with moderate water in the winter and low water in the summer.

“We make sure that people are sensitive to the seasonal distribution of water,” Perry said. “Organize plants into two plant groups. Those that need regular water so they don’t get moisture stress, and those that are very nicely adapted to moisture stress… Then be mindful that within those groups, you have low, moderate and high preferences for moisture.”

To simplify further, Perry lists the plant factor and irrigation group at the top of each plant entry, along with a chart that notes in which of California’s 24 plant climate zones that particular plant will thrive.

He also provides a master checklist, along with 33 plant lists based on such attributes as woodland garden plants, flowering trees, and fragrant flowers and foliage.

Diving Into the Details

Hot Lips sage

Perry said he’d be happy if most homeowners get that far in organizing their gardens.

And you can easily stop there. But for folks and professionals who want to push further, Perry dives into the science of evapotranspiration (ET), which describes how much water a plant loses to evaporation and transpiration.

By comparing a plant’s ET to a region’s annual rainfall, the thinking goes, you can come up with a rough idea of how much irrigation is necessary, and on what kind of cycle.

Farmers have a long history of doing just that with any number of crops. About 30 years ago, Perry said, UC Cooperative Extension took the idea and tagged just one crop — cool-season, tall fescue grown 4 to 7 inches tall — as a reference plant by which the watering needs of other ornamental plants could be assessed.

“Cool-season, tall fescue has been deemed to be consistent in its water needs and very responsive to lack of moisture,” Perry said. “It became the reference crop, setting the high-water bar as to what it would need.”

The actual rate (ETo) then varies by where you live.

For instance, Perry presents charts showing ETo rates in 13 California cities. Cool, coastal San Francisco has the lowest ETo: cool-season, tall fescue needs 35.1 inches of water a year to thrive there. Meanwhile, in blazing hot Needles, the same fescue’s ETo is a whopping 92.1 inches of water a year.

After ETo comes rainfall. The difference between the two numbers will help you figure out how much you’ll need to irrigate.
Numbers from several Central Coast weather stations are online at

In Nipomo, the ETo from July 2009 through June 2010 was 43.6 inches of water. Precipitation during the same period was 17.65 inches, which resulted in a shortfall of 25.95 inches.

In Santa Ynez, the ETo was 50.69 inches; precipitation was 23.4 inches of precipitation and the difference was 27.29 inches; in the Goleta Foothills, 50.71 inches vs. 26.61 inches, a difference of 24.10 inches; and in Santa Barbara, 44.80 inches vs. 13.89 inches, a difference of 30.91 inches.

New Gold lantana

Fortunately, most plants don’t need — or even want — as much water as is necessary to maintain that cool-season, tall fescue at a height of 4 to 7 inches.

That’s where Perry’s plant factors become important again, since most plants need only high, moderate or low amounts of water, comparatively speaking.

But what complicates matters is that you still have to account for soil type, wind and how much moisture moves in off the ocean, as well as the efficiency of your irrigation system.

Throw in a few more calculations and you can get really confused.

However, Perry illustrates the concepts with such easy-to-read charts that it all becomes clear.

Plus, he constantly reinforces that you’re mostly there if you simply group your plants according to one of the two irrigation groups, then within the three different plant factors.

Perry takes out even more guesswork by presenting palettes of plants that are compatible with 27 common landscape trees, such as crape myrtle, jacaranda, coast live oak and California fan palm. For each palette, he lists companion trees, shrubs, vines and perennials. In addition, he notes horticultural preferences, aesthetic character, seasonal moisture and irrigation schedules.

About Bob

Seaside daisy with sulfur buckwheat.

Bob Perry has been urging home gardeners and professionals to attune their designs to the natural environment for more than 30 years.

He has been a licensed landscape architect since 1972, and is a long-time landscape architecture professor at Cal Poly Pomona, UCLA Extension and USC. He has designed demonstration gardens for a number of communities, including Pasadena, Malibu, West Hollywood and at Cal Poly Pomona. He has also been a member of the WUCOLS committee since its inception, a group that has been charged under the state’s model water efficient landscape ordinance with categorizing landscape plants according to their watering needs.

Perry’s two previous books were also about plants and water conservation: Trees and Shrubs for Dry California Landscapes, 1980; and Landscape Plants for Western Regions, 1992.

Perry’s new Landscape Plants for California Gardens retails for $87.50. It’s available online at both his website,, and, at a discounted rate of $78.75, which includes sales tax and shipping.

Seeds of Wisdom

Rather than a one-season-fits-all approach, Bob Perry’s “Landscape Plants for California Gardens” introduces a new, ground-breaking way to design and irrigate California gardens.

Copyright, Joan S. Bolton. All rights reserved. Reproduction of text or photos in any form is prohibited without written permission.

2 responses to “Summer Reading: Bob Perry’s Landscape Plants for California Gardens
  1. Bob Perry has confidence in us gardeners or he would not have gone to the trouble. Sounds like I owe him the honor of putting that book in my library before I start serious renovation next year. THANK you for sharing.

  2. I have frequently refered to Bob Perry’s first two books. This new volume sounds like the ultimate reference book for serious gardeners and professionals in water challenged Califronia. I have to have it!

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