by Bruce Bennet • The last three years have given us some of the increasingly hottest weather on record and forecasts for the next decade really don’t provide us much hope for the cooler, “normal” weather cycles. The next logical step in landscape development includes the issue of global warming in our part of the world. Let’s look at some existing plants that are being trialed as horticultural candidates which are up to the challenges of heat and drought.
For the past two years, I have been part of an evaluation process of some 15 different types of plants which may benefit our area’s gardens. The University of Washington Botanical Gardens joined a multi-year endeavor initially begun by the University of California-Davis California Center for Urban Horticulture and is funded by the U.S. Department of Agriculture. The expanded trials now include garden plots at the UC-Davis, the University of Washington Botanical Gardens, the South Coast Research and Extension Center, the University of Arizona, Utah State University, Oregon State University, and the North Willamette Research and Extension Center.
These Landscape Irrigation Trials are a longitudinal research project will help identify some of the best water-wise plants for our region. The findings will help the live-goods trade and gardeners of Puget Sound make smart plant choices for the hotter, drier summers climate scientists predict for the years ahead. From the ranks of the wholesale nursery industry, garden centers, Certified Master Gardeners from King County, and more, evaluators will rate some 350 plants in terms of their foliage, flowering, pest tolerance/disease resistance, vigor and overall appearance (aka, the “WOW factor”).
The plants which thrive best with the lowest amount of irrigation will be classified as the “winners,” and will be recommended to the green industry and Northwest gardeners, similar to the suggestions from the Great Plant Picks program through the UW’s Center for Urban Horticulture.
As this is only the UW’s second year participating in these trials, there is not, as yet, a list of drought-tolerant plants for the Northwest to recommend. You can, however, visit the UC-Davis website. Remember to select plants to research for your landscapes which grow well in our US Hardiness Zones (Zones 7 & 8). From these past two years of trials (and 20-years of hands-on experience), I have come away with a short list of my own favorites from the trials. Among these full-sun (six+ hours/day) loving candidates for your consideration are:
Chaste Tree (Vitex agnus-castus) ‘Blue Diddley’ is a dwarf (6’ x 5’) version of the straight species which can grow quite large (18’ x 15’). As a Mediterranean native, Vitex has proven to be extremely drought tolerant. This compact, intensely colored, freely blooming shrub could find a space in a mixed border or on a sunny condo deck. It would also be a great alternative to those who want the “look” of the invasive Buddleia (Butterfly Bush) in their yards.
Crape Myrtle (Lagerstroemia indica) ‘Center Stage Red’ is another great color counterpoint in the landscape. In late summer, this 12’ x 10’ small tree/large shrub commands the spotlight with its deep burgundy-to-black leaves and red flowers. It naturally grows with a narrow, space-saving habit and needs minimal pruning. If you find the leaves on your Redbud or Japanese Snowbell crisping during our increasing heat domes, a Crape Myrtle just might be the new urban setting tree for your yard. An added bonusthese plants offer is their disease and deer resistance.
Maiden Grass (Miscanthus sinensis) ‘Bandwith’ is the new gold (banded) standard in a dwarf (3’ x 3’) Miscanthus. This compact Maiden Grass has green foliage with pronounced yellow banding. The habit is solidly upright like ‘Zebrinus’ but stands half the height. Bandwidth flowers late in the season and adds extra interest to fading gardens. It makes a great landscape accent or a “thriller” in containers. Miscanthus is versatile from a design standpoint; it can be used as a single specimen, for mass plantings, or screening or in large containers. Even though it dies back in early winter, it will provide a buff-colored presence of winter interest which birds will enjoy for the seeds provided the homeowner for the vertical visual show.
Nine Bark (Physocarpus opulifolius) ‘Little Devil’ (4’ x 3’), has an upright spreading habit, fine-texture and dark foliage that sets it apart from the many greens of the landscape, and provides a nice contrast and can replace thorny barberries in the yard. This less-than-thirsty shrub is definitely easy-care and requires little, if any, pruning. Additionally, it is virtually free from pest and disease issues, and adapts well to wet or dry soil. Clusters of small purplish-white flowers bloom in June that contrast nicely with the burgundy foliage.
Rose (Rosa x) Oso Easy® ‘Urban Legend’ is a true-red excellent carpet rose (2’ x 3’) that blooms from early summer until hard frost and without trimming and deadheading, no less. The glossy green leaves seem to be pretty resistant and usually have no need for fungicides. This plant’s size and rigor make it an excellent candidate as a ground cover, edging or sunny spot that could use a bit more summer color. As with all of the plants on my list, once established, they require far less water than others in their taxa. I’d recommend an application of a granular fertilizer in spring and pruning in early spring.
A few other trial recommendations for you to consider include Bluebeard (Caryopteris x clandonensi), Buxus ‘Little Missy’, California Lilac (Ceanothus thyrsiflorus) ‘Victoria’, Chaste Tree (Vitex agnus-castus) ‘Summertime Blue’, Cotoneaster x suesicus ‘Emerald Beauty’, Nine Bark (Physocarpus opulifolius) ‘Diablo’, Rose ‘Blushing Drift’ and Rose of Sharon (Hibiscus syriacus) ‘Pink Chiffon’. Check out some of these drought-tolerant plants and win on several fronts; hold onto a bit more of your public utilities dollars, have a better looking yard and save some time watering your yards Happy gardening all!
Contributing garden columnist, Bruce Bennett, is a Washington State University Certified Master Gardener, public speaker and Seattle-area garden designer. If you have questions concerning this article, or have questions concerning your garden, contact Bruce at gardenguy4u@gmail.com.