Are Native Plants Always Better?
The 20th Street garden was planted about 3 years ago on October 6, 2012. At that time, 36 different plant species went in on 20th, Alabama and Florida Streets, about 2/3 of them native to California. (Note: The California Native Plant Society defines native plants as any species that was present before Europeans arrived.)
(Photo 2: Bunny Tails grass has survived many car bumpers on Florida St)
Since then a lot has happened – 3 years of record low rainfall and record high temperatures, in addition to the usual problems that plague all sidewalk gardens: feet, dogs, construction, cars, dumping, etc.
(Photo 3: Purple-flowered sea lavender with California fuschia and purple needlegrass)
Now in 2015, we still have a fair amount of diversity: 26 species are still present in the garden, with more than half of them being California natives. But when we look at the species in “good” condition, the story changes. 11 species are healthy and productive, with 5 of these being native and 6 being non-native. Non-natives are slightly outperforming natives on 20th Street.
How can this be? At first, it would make sense that plants that have always grown in a certain area would be healthier than exotic species. That’s not always the case, for the following reasons:
- The native environment has been altered. During development, soil may have been taken away or added from somewhere else. Creeks and waterways may have been diverted or blocked. Tall buildings change wind and sun patterns. A location may have supported a number of native plants in the past, but everything’s different now.
- Plants can be incredibly picky about where they grow. The state of California is a political boundary containing many eco-systems: shoreline, marsh, forest, grasslands, etc. Within these different eco-systems, plants develop a certain niche. Some grow in the open, others in the shade of other plants. Some grow on riverbanks, others a little uphill from water. When you walk in nature, you can see how various plants colonize areas where their preferred conditions are. If we cannot re-create their preferred conditions in the garden, they won’t thrive. It’s that simple.
- Many non-natives have an edge. Within any habitat, a number of insects and diseases also evolve to feed on certain plants. When we import a plant to a different habitat, their pests may be left behind. Without these local pests to slow them down, non-natives can grow faster and larger, out-competing the natives.
Here is a brief description of the 11 plant species doing the best after 3 years:
- Toyon (Heteromeles arbutifolia) This shrub is not only drought-tolerant but can grow in either shade or sun, multiplying the habitats it can thrive in.
- Wild Lilac (Ceanothus thyrsiflorus) This drought-tolerant shrub has a unique ability to convert nitrogen from the air into soil nitrogen, allowing it to grow in nutrient-poor soils.
(Photo 4: San Francisco gumplant in front of Salumeria)
- San Francisco Gumplant (Grindelia hirsutula var. maritima). This unassuming plant with cheerful yellow daisylike flowers quietly held its own while its competitors faded away. Now that it has more space to itself, it has spread considerably. This variety is specifically native to the San Francisco peninsula.
- California fuschia (Epilobium canum). The fuzzy silver leaves help reduce water loss, and the neon orange flowers produce many seeds, allowing new plants to sprout easily.
- Purple Needlegrass (Nasella pulchra). This is the state grass of California. It’s growing on the corner of Alabama and 20th interspersed with California fuschia and non-native sea lavender.
- Sea Lavender (Limonium perezii): This purple-flowered plant, beloved by bees and butterflies, is native to the shores of the Canary Islands. Ironically, it is endangered in its native habitat, but shows no sign of waning here.
(Photo 5: Strawberry Tree flanks both sides to the entrance of Central Kitchen.)
- Strawberry Tree (Arbutus unedo ‘Oktoberfest’): This Mediterranean native is well adapted to drought and coastal weather conditions. It would probably produce more flowers and fruit if we had more rain.
- Glossy Privet (Ligustrum lucidum): Since being planted in 1987, these street trees on 20th survived years of neglect and overpruning. Native to China, they are now found throughout the United States.
- Sweetshade (Hymenosporum flavum): Despite being native to Australian rainforests, these trees have prospered on the baking hot sidewalk of Florida Street. They have been getting TLC in the form of discarded ice being dumped in the tree wells.
(Photo 6: Pink Knotweed never stops blooming in the tree wells on Florida)
- Pink Knotweed: (Persicaria capitatum) This pink flowered ground cover can be found in neglected sidewalks throughout the city. An Asian native, it is used in Chinese medicine.
- Bunny Tails grass (Pennisetum ‘Bunny Tails’): Native to Asia and Australia, this grass has thrived on Florida Street despite the challenges of drought, parked cars and trash dumping.
Native plants still hold many benefits, including supporting local birds and insects for food and shelter. Yet local creatures can adapt. The most famous recent story is that of the Western Tiger Swallowtail butterfly. Normally it would lay its eggs on the California Sycamore, which grows by streams and rivers. However, it has adapted to lay eggs in the closely related but non-native sycamores (London Planes) on Market Street. Because the butterfly can adapt, it can survive.
Not every organism is as adaptable, and native plants are still important. But as the environment changes, it’s heartening to know that life in its many forms has a fighting chance.
Ellyn Shea is a gardener and consultant in San Francisco. Visit her at http://www.garden-guidance.com