Learning to Love California Gold : Part Two
As a self-professed plant geek, one of the most inspiring things to me is the abundance and diversity of life. Even after centuries of study, we continue to discover new and fascinating things about the workings of the natural world. In 1993, the first edition of the Jepson Manual estimated 5,862 species and subspecies of plants native to California. A 2001 study by the California Native Plant Society put that number closer to 6,500 species, and the current edition of the Jepson (now available as an online interchange) catalogues about 7,600 species, subspecies, and varieties native to California alone. Even a casual study of this diversity, and the many thousands more species that can be found across the globe, reveals patterns (some intuitive and some subtle) that provide insight into a plant’s origin. In looking at a plant’s form, its leaves and flowers, and its growth patterns, we can see evidence of its evolutionary history – the visual trademarks that distinguish it as uniquely able to survive in its native environment.
1)Desert plants store water in succulent leaves or stems, and defend that precious water against herbivores with thorns. Cacti and other succulents growing in the Huntington Desert Garden by Pamla J. Eisenberg/CC BY-SA 2.0
2) Understory plants often have large dark leaves to maximize photosynthesis. Alocasia micholitziana ‘Frydek’ by James Steakley (Own work)/CC BY-SA 3.0 or GFDL via Wikimedia Commons.
3) Plants adapted to windy conditions (like near the shoreline) often have creeping forms, small leaves, or rosettes of leaves close to the ground to minimize wind resistance. Eriogonum latifolium (coast buckwheat) and Erigeron glaucus (seaside daisy)by oliveoligarchy/CC by 2.0
Using plants that adapted to thrive in our local climate makes sense as a simple way to reduce the amount of water, fertilizer, herbicide, and labor needed to maintain landscapes in the built environment. It also allows us to cultivate an aesthetic that is uniquely California and celebrates the natural diversity of our state. Many of our California native plants, as well as plants that originate from other dry-summer regions of the world such as the Mediterranean basin, Australia, South Africa, and central Chile, have adapted to go months without rainfall. Their coping mechanisms generally fall into one of the following categories:
- Drought avoidance – plants avoid drought stress altogether with deep roots to find water, leaf shapes to minimize water loss, or dormancy during the dry season. Drought-avoidant plants won’t stay green and growing in the face of severe drought stress.
- Drought tolerance – thanks to slowed growth rates, altered photosynthesis, or other cellular changes, drought tolerant plants can still grow and thrive even after months without rain.
- Low water use – unlike drought tolerant or drought avoidant plants, some plants use very little water on average, but will not survive a prolonged period of dryness. Many hybridized or horticultural varieties of our native plants fall into this category. They would not survive in a non-irrigated landscape, but will do beautifully if regularly irrigated, even in small amounts, in a cultivated landscape.
Many plants employ more than one water-saving strategy within these categories, and some that have the most impact on a plant’s use in the built environment include:
- Slow growth – Many woody drought-tolerant species grow slowly, taking 5-10 years from the time of planting to reach a mature size. While the delayed gratification may frustrate those looking for instant impact, the tradeoff of a long life span means that they will look great for years to come. Examples include manzanitas (Arctostaphylos spp.), and oaks (Quercus spp.).
- Summer dormancy – The largest group of summer-dormant plants is perennial grasses, which grow in the winter and spring and slowly fade to gold during their dormant state in the summer. A few woody plants are summer-deciduous, including California Buckeye (Aesculus californica) which is one of the earliest plants to leaf out in spring but will drop its leaves early during a dry summer.
Short life cycle – Annual plants also exhibit a kind of summer dormancy, but because their life cycle is only one growing season, this dormancy occurs between generations after the plants flower, set seed, and die in the spring and summer. Seeds lay dormant during the dry season, springing to life with the winter rains.
- Succulence – Like cacti and agaves, some plants store water in succulent stems and leaves, enabling them to survive long dry periods where water is unavailable.
- Small fuzzy leaves – In hot sunny areas where more than enough light is available for photosynthesis, small fuzzy leaves can help keep plants cool and minimize water loss. Small hairs on the surface of the leaves create an insulating layer that minimizes air flow across the leaf’s surface and keeps leaf temperatures low. Plants with fuzzy leaves often look grey, silver, or dusty green and can infuse a variety of colors and textures into a plant palette. Examples include Flannel bush (Fremontodendron californicum), lavender (Lavandula spp.), and sagebrush (Artemisia).
By understanding the mechanisms that plants use to save water, we can design landscapes that meet both the aesthetic expectations of landscape users as well as today’s standards for resource-use reduction. Moreover, we have an opportunity to create landscapes that are dynamic and vibrant, changing not just with the seasons but over time as they mature and evolve. In a newly-planted landscape, masses of quick-growing grasses and perennials can provide texture, color, and movement while slower-growing shrubs are still small. As the woody backbone of the landscape fills in, colorful perennials and textural grasses can serve as accents against a mature evergreen backdrop. With all the stunning variety of the natural world around us, it seems a shame to design a landscape that is static and unchanging, especially if we can achieve longevity and durability while still allowing for change over time. A rush of green followed by an explosion of color with winter rains and warm spring temperatures, the dappled shade of oaks in the summer, and golden grasses nodding in the autumn breeze. As landscape architects, we embrace the opportunity to create places that inspire, delight, and help us connect to the beautiful place we call home!
Brenna Castro is a Job Captain in our Sacramento Office and is also one of our resident Plant Experts!