by Charlene Burgi
This past weekend I was able to catch up on some reading. A stack of magazines had been set aside in wait to reveal wonders within the pages of creative designs, new plant ideas and general outdoor goodies.
Fourteen pages into the first magazine, I was taken by surprise. Did you know that this January, after 22 years, the U.S. Department of Agriculture (USDA) made changes to their plant hardiness zone map? As you know, a plant’s “hardiness” is its ability to tolerate adverse conditions such as freezing temperatures. The zones help gardeners choose plants that will survive and thrive in their area. The USDA’s planting zones were re-analyzed based on the average lowest winter temperatures over the past 30 years, with the result that typically warmer-zoned areas shifted toward the north.
For example, in the past San Rafael was classified as zone 10 with expected low temperatures ranging between 30 – 35 degrees Fahrenheit. Now it is zone 10a with expected lows of 35 – 40 F. This is no big deal for Marin’s temperate climate, or so it would seem. A complication is that the USDA planting zone map differs from the Sunset Western Garden zone map, which shows San Rafael in zone 17 with low temperatures ranging from 23 – 36 F. The difference is enough to make or break frost-tender plants in our garden.
Bougainvillea is a great example of a plant that could take the temperature at 35 F, or become compost material at 23 F. The plant is excellent for water conservation; it requires minimal care and produces maximum high color in bloom. It thrives at my house in Novato. It has been there for over 50 years and produces gorgeous brackets of red every summer. A cold snap can send it into dormancy, but the plant always recovers. The section of Novato where my plant lives is classified as zone 17, like San Rafael. However, my plant has the bay influence, is facing due south and is right up against a protected area next to the house. In another zone 17 garden lacking those same growing conditions, it could not survive.
Who, then, are we to believe? The bottom line: Nobody knows a garden as well as the person who lives and works in it. Only you know the hot spots, the areas that puddle, the wind-protected microclimates. Only you know if you have seen the frost lay on the ground for hours after your morning coffee. Only you know if your garden tends more toward zone 10a or zone 17 temperatures. Only the engaged gardener will know which plant-hardiness database is most helpful for making proper plant selections for a healthy, thriving garden. And did I say this information was no big deal for Marin’s temperate climate?
On to page 15: Shade Loving Plants for a Dry Landscape Garden …
We have just a couple of spaces left in our FREE Irrigation Essentials workshop Saturday, April 14, 10:00 a.m. – noon at the Mill Valley Community Center. Learn how to get your system ready for irrigation season and how to manage it to get the most from every drop. Call Wendy at 945-1521 to reserve your spot.
Then join us at the Earth Day Marin Festival on Saturday, April 21, 11:00 a.m. – 6:00 p.m. at Marin Civic Center Lagoon Park. This free, fun, family-friendly event includes music, organic food, interactive activities, speakers, local artisans and more. MMWD will be there celebrating our 100th anniversary along with other Marin public land agencies—drop by to say “hello”!