Much of gardening is trial and error, some would say.

Others learned gardening secrets handed down from generation to generation as tried-and-true wisdom.

These methods probably work just fine, but one group of gardeners relies on scientific research to guide their efforts.

That’s the premise behind “The Tucson Garden Handbook,” the guide put out by the Pima County Master Gardeners.

Their third edition is updated with the latest information gleaned from scientific papers across the country, including findings from the University of Arizona.

“It’s all in alignment with what comes out of research from the University of Arizona and other sources,” Deborah Green says of the new handbook, which was released in January.

The book uses the same information that is taught to people in the UA’s 50-hour Pima County Cooperative Extension master gardener training course. Their mission is to educate the public on scientifically based practices.

“This is like the CliffsNotes of the (master gardener) manual,” Murray DeArmond says. “It’s boiled down to the essentials.”

Green, a master gardener for five years, and DeArmond, a 16-year master gardener, are the main authors and editors of the greatly expanded version of the handbook’s second edition.

They pulled information from well-regarded local organizations, such as the Rose Society of Tucson, and master gardener programs throughout the United States, as well as research from the UA College of Agriculture & Life Sciences. They also had local master gardeners review the information to make sure it’s up to date.


Some information goes against conventional wisdom.

For instance, while expert gardeners advise pruning a tree during the plant’s dormant period, the handbook gives this advice based on scientific observation:

“Our desert native trees may be pruned during the summer months. These plants heal efficiently after pruning even in the heat of summer.”

Another example involves fertilizing citrus trees. The back story is not included in the handbook but in a fall 2015 master gardener newsletter.

The extension office in Yuma found in extensive studies that the recommendations were inadequate for the Arizona climate and instead were beneficial mostly for the California growing season.

So the standard recommendation to fertilize near Valentine’s Day, Memorial Day and Labor Day does not appear in the handbook.

Instead, local master gardeners suggest January-February, March-April and May-June for feeding orange, tangerine and grapefruit trees; January-February, March-April and August-September for lemon and lime.

The authors admit in the handbook that not all gardening issues can be solved by science.

“... There are no research-based, definitive rules for watering your garden,” according to the handbook.

The reason is that there are too many variables, among them soil structure, weather conditions and seasons.


When the original handbook was published in 2009 and updated in 2011, it was organized around five demonstration gardens that the master gardeners tended as educational displays. Each garden’s committee wrote its respective section.

With today’s 12 demonstration gardens, much of the advice overlaps. Green and DeArmond, who were asked to create the third edition, decided to reorganize the information into broad categories.

Much of it is still presented by plants: natives, flowers, roses and edible gardens, for instance.

Garden creation and maintenance is gathered into one chapter, which includes new sections on companion planting and pest management.

Container gardens of all types of plants are grouped into a single chapter instead of spread out depending on what one puts in a pot.

A chapter also expands on the previous editions’ information on the master gardener program itself, including its public events. It lists books, websites and guides often used as master gardener resources.

References are cited so that gardeners can delve more deeply into the research behind the recommendations.

“This is an easy reference, especially for new gardeners to the valley,” Green says. “They would have things that would help them be successful as new gardeners.”

Adds DeArmond: “This will reassure people that they can have a highly successful garden.”

Contact Tucson freelance writer Elena Acoba,