To support public health and education: grow trees

By Lauren Lewis

When you stumble upon a street where the sidewalk trees are so big they form a full canopy over the road, it just feels good. (I’m picturing 24th Street in the Mission as an example, from Mission to Potrero.) Something about the completeness of the shade, or the feeling of outdoor enclosure, is rare and lovely in an urban setting. Because they are big, long-lasting plants, trees provide structure and large-scale greenness in a city, and it’s very noticeable when they’re lacking. Some interesting recent research has tried to identify the more nebulous benefits that humans derive from trees, and city governments, including San Francisco’s, are starting to prioritize the urban forest.

IMG_5393In 1982 the government of Japan began a campaign encouraging “shirin-yoku”, or forest-bathing, to promote public health. Since then, various studies have shown physiological benefits, like lower cortisol level and lower blood pressure, from time spent in a forest as compared to city. To me this is somewhat unsurprising, though, given the noise and stresses of the city as compared to a natural setting. What’s really interesting is work that has tried to pinpoint trees as the health-promoter, compared to other natural elements. One such study found that high school students whose view out the cafeteria windows was filled with trees showed higher academic performance than those whose views were mostly other landscape elements like lawns. Thoughtful landscape design that mimics wild nature can have benefits that go beyond aesthetics.

Looking at the same idea in reverse, i.e. the public health impact of lost tree cover, yields similarly compelling evidence. When a beetle infestation caused 100 million trees to die across the eastern half of the United States a few years ago, a forest service researcher looked at how human mortality in those areas was affected. He found that infested counties had significantly more deaths per year from cardiovascular and respiratory diseases than uninfested counties, controlling for other factors. Even controlling for income, race, and other factors that impact health, the tree mortality provided a significant explanation for human mortality.

San Francisco’s 13.7% tree canopy is lower than most other major American cities, including Chicago, LA and NYC. Some of this is attributable to the fact that San Francisco’s land was never a treed environment; it was dominantly a shrubby, grassy landscape. Especially in the western part of the city, the fog, wind, and soil properties create a challenging environment for trees. According to Allegra Mautner, tree care manager at Friends of the Urban Forest (our city’s awesome urban forest nonprofit), trees that are planted in the western part of the city have only a 50% survival rate, as compared to the norm of 80%.

But now that we’ve got a dense urban environment on this land, trees are crucial for the all the benefits they provide: quality-of-life, human health, habitat, heat-control, carbon sequestration etc. The city government recognizes this, and in 2015 the Board of Supervisors adopted the Urban Forest Plan to begin building a stronger and larger urban forest. In the 2016 election that effort got a boost when SF voters approved a proposition that moves responsibility for street trees from property owners back to the city. A funding challenge still exists to fully implement the switch, but this change has the promise to bring more consistent and better care to our street trees.

Striving for ant-human mutualism

By Lauren Lewis

The concept of ecosystem services gained recognition and common use among ecologists and policy makers only within the last 20 years or so. Ecosystems services are the benefits that humans collectively receive from the functioning of ecosystems. It’s the natural processes happening around us that we don’t control but that make the world as we find it. There are many examples (trees respiring oxygen, bees pollinating crops, etc), but specifically in an urban environment, the insects around us arguably provide some of the most crucial ecosystem services. They’re barely noticeable, but hugely present.

By numbers, ants are a massive presence in cities and they provide the crucial service of eating our trash. One study estimated that there are 8000 ants for every rat in New York City and 2000 ants for every human. The research team for this estimate is led by Amy Savage, a PhD ecologist who is a leader in the effort to understand non-human urban species and their interactions with each other and with us. Her work in NYC showed that arthropods, mostly ants, carry away and digest as much discarded food as all vertebrates combined (that’s rats, squirrels, etc). Ants are active cleaners of our cities.

In the garden, we’ve long recognized that ants are among the myriad creatures necessary for healthy soil; ants aerate soil by digging and they help break plant material down into smaller pieces for digestion by worms. But a recent study illuminated another fascinating benefit of ants for soil: the “aggregate mulch” churned up by burrowing carpenter ants can reduce evaporation from the soil surface. The burrowing action of these ants leaves soil clumps with a particular texture behind them. Greater thickness of this aggregate mulch layer was associated with lower soil evaporation rate, particularly in the hours right around noon, when evaporation is highest. At Small Spot Gardens we are big advocates of mulch for its ability to reduce water needs, so now we know that supporting ant populations could be right in line with that goal.

Various ant species behave in widely divergent ways, so supporting ant populations can mean a lot of different things, but overall, there’s a consistent theme of leaving some wildness for ants to use. For epigeic ants, those who inhabit only the top layer of soil rather than burrowing and nest in existing cavities, presence of appropriate nesting materials is crucial. One study of epigeic ants and their nesting preferences found that ants showed a preference for certain cavity types (“large” 6mm wide hollow twigs) and that all nest types were more abundant in forest sites than in vacant lots or gardens. The findings suggest that efforts to mimic a forest environment (with leaf litter on the ground!) can support ant life.

The Bay Area is home to over 100 species of ants, but unfortunately the introduced Argentine Ant has driven a lot of them away by outcompeting them here and across California. The threatening presence of the Argentine Ant is all the more reason to see your garden space as a potential haven for other ant species. The plant litter you decide to leave behind instead of transferring to the green bin might mean home for a native ant colony.

Less-is-more Gardening for the Birds

By Lauren Lewis

When it comes to active garden maintenance, the Small Spot crew almost always argues that less is more. We don’t say less is more out of laziness, but rather out of our understanding of the garden practices that can create beauty and sanctuary while simultaneously allowing wild ecological relationships to thrive. The goal of supporting bird life in the garden provides a wonderful example of our favored approach: thoughtful ecological planning followed by less-is-more maintenance.



House finch pair in the Presidio, photo by Will Elder,

Despite the density of San Francisco, our city is habitat for a huge variation of bird life. Besides supporting all the common garden birds that live here year-round (house finch, red-breasted nuthatch, black phoebe, cassin’s vireo, to name just a few), San Francisco is a key link in the Pacific Flyway, the biannual north-south migratory path of hundreds of bird species. Backyard gardens in San Francisco collectively cover more land than all our city’s wild spaces, so the way we choose to use them has a real impact on all those migrant and resident birds.

Designing your garden to include at least one “wild” section is key for providing landing spots where bird feel safe. Wild habitat has tangles of vegetation and bits of overlapping rocks and fallen branches, which can be tempting to remove or clean up when they occur in the garden. But this would not qualify as less-is-more. Retaining some of those elements (i.e. ignoring them) makes a more inviting space for birds.

A water source that gets refreshed is also important, but it doesn’t have to be a real bird bath; a bucket with a drip emitter inside that constantly refreshes the water can serve the same purpose. And of course a variety of plants that produce nectar, seeds, and fruit will mean your garden can host birds with different feeding patterns. The less-is-more lesson here is: let plants go to seed. If you manage them a lot you’ll end up with less garden-grown bird food and therefore fewer birds.

Now if you’re like me, then the idea of garden management for birds becomes more intriguing when you can focus your efforts on one species or a handful of species. If that’s the case, check out the SF Planning Department’s Green Connections Plan. Created in collaboration with Nature in the City (of the Green Hairstreak Project that I mentioned in a previous post), the Green Connections Plan is billed by the Planning Department as a strategy to make traveling through SF by foot or bike more pleasant and viable by creating routes that deliberately connect parks and open spaces. The added benefit is that these routes can be used by non-human species too. In fact each of the planned 24 routes crisscrossing the city is named for the species it’s meant to support, and many are birds.


Cedar Waxwing in John McLaren Park, photo via

One example is the sleek Cedar Waxwing, whose designated route is Page Street, from Market to Golden Gate Park (it doesn’t mean this species only lives along that route, but rather it was chosen as a representative of this Green Connection route, which is within its normal habitat). This bird is unusual in its largely fruit-based diet, which means there’s a manageable handful of garden plants you could plant to help support it, for example toyon and elderberry. The new SF Plant Finder, a part of the Green Connection Plan, is a fantastic gardeners’ resource that lets you explore and choose plant species with something like the Cedar Waxwing in mind. What I like about Green Connections is that it can help you choose a species to support and the plants needed to do that, and then if you practice some less-is-more maintenance, your garden can play an important role in the lives of our city birds.

Weeds as Mindset

By Lauren Lewis

A weed is simply a plant growing where it is not wanted. But there’s nothing inherently ugly or unpleasant about garden weeds as a category; in fact many are quite lovely, and not so different from their relatives that we plant on purpose.


On the left is oxalis pes-caprae, likely dominating your garden at this very moment. On the right is oxalis vulcanicola, a dainty, colorful addition to borders and containers.

Weeds are only unwanted because their impressive growth characteristics allow them to spread quickly in places they haven’t been invited and outcompete more desired plants. They are plants that have evolved to be the earliest, fastest growers after a disturbance in the environment. A disturbance could be a fire, a flood, a fallen tree that leaves newly exposed soil, the planting of a garden. Weed seeds are fastest to germinate, and their seedlings grow quickly, collecting more resources than their non-weedy neighbors. Weedy plants typically flower faster than other plants, and many have seed characteristics that aid wide dispersal, such as parachute shapes (like dandelion puffs) or hooks for velcroing to fur and pants (burrs).

All of these characteristics mean that weeds can dominate a disturbed environment soon after the disturbance. In a typical garden the disturbance is constant, which means the weeds are also constant. But in a natural environment following a single disturbance event, the pioneering weeds slowly change the environment in ways that encourage growth by the next types of plants- shrubs, small trees, etc. The weedy growth builds organic matter in the soil, the roots change soil structure, the plants can change the soil’s pH and mineral composition.

Weeds provide these crucial services to recovering natural environments, and despite their bad rap they also provide various under appreciated services to humans. For example, weeds and their roots protect our urban, oft-disturbed soil from erosion during rain. In a garden setting mulch can provide some of that same service, but weeds are substantially more effective since they are tethered to the soil by their roots.fullsizeoutput_28a4

Grasses are a massive category of weedy plants that provide humans with another crucial service: grains as a food source. Grasses are highly adaptive and dominant in habitats everywhere except Antarctica, with fast growth and a low growth point that lets them survive trampling and grazing. The earliest agriculture was cultivation of grasses for grain, and today grasses account for the majority of agricultural crops (wheat, rice, corn!).

For these reasons and many more, some creative folks are trying to give weeds a boost in reputation, using a variety of interesting methods. Spontaneous Urban Plants is a crowd-sourced mapping and research project aimed at noticing, understanding and celebrating the various benefits of the weeds growing in New York City. Weeds catalogued by the SUP project are categorized by the particular benefits they perform, including urban heat mitigation, carbon sequestration, food, wildlife habitat and many more. The project aims to subvert the negative assumptions about weeds in a way that can positively influence urban design.

Mona Caron is a muralist and photographer who is using her art to raise weeds up a notch. She happens to be San Francisco-based, and you’ve likely noticed some of her iconic murals around the city (above). Caron views weeds as under appreciated in their beauty, so she paints murals of giant healthy weeds, allowing her subjects to demand the attention she thinks they deserve.


Ribwort plantain in San Francisco. Photos via


At the small scale of a single garden, one can carry out the same kind of garden rebellion by simply questioning the decision to remove a weed. Is it preventing another plant from growing? Using fresh eyes, how does it look to you? Some plants that previously would have been pulled automatically might hold a new form of appeal. And even if you can’t find their beauty, you can boost the health of your soil by cutting weeds off at the ground level instead of pulling. Cutting the weed off and leaving the roots intact helps maintain soil structure and avoids the soil disturbance that patient weed seeds are waiting for. By keeping all or part of our weeds around, we can create healthier and maybe even more interesting natural spaces.

The literal power of flowers

By Lauren Lewis


Flowers are the garden’s showstoppers. Even the least botanically-inclined can appreciate their color and fragrance, and for Valentine’s Day they’re a near requirement as a sign of your love. For the plant itself, the flower allows for reproduction. Most flowers contain both pollen (the male contribution to reproduction) and ovules (like eggs) that accept pollen and turn into seeds. The colorful petals have evolved to attract critters like us, though more accurately insects and birds, who visit the flower and unknowingly carry the pollen to another flower. Plants rely on the beauty of their flowers for their continued existence.

In an urban environment, we can can use our love of flowers for a good cause. You’ve probably seen press about honeybee population declinewhich is concerning because of its impact on agriculture, but you may not have heard about the same problem happening among native pollinators (honeybees are originally from Europe). Hundreds of native pollinator species -bees, butterflies, moths, hummingbirds- are threatened by lost habitat, chemical use, and other factors. The good news is that we urban residents have some agency over the survival of those diverse pollinators depending on how we choose to use our open spaces, and especially how we incorporate flowers.

In one study of bees in urban parts of California’s central coast, researchers found that bee diversity and abundance were higher in gardens with more abundant flowers, more plant diversity and more open ground as opposed to mulch. The flowers provide bee food, and the authors theorize that plant diversity and open ground likely provide nesting habitat for varied bee species. The authors found that these garden-level factors were more strongly associated with bee population health than larger scale factors such as how developed the surrounding land is. This finding illustrates the potential power that a garden owner can have in the effort to protect pollinators.

Seattle’s Pollinator Pathway is a fantastic example of people using their power of garden design to support pollinators. Founded by Sarah Bergmann, the Pollinator Pathway is a mile-long, 12 inch-wide stretch of curb gardens planted with plants picked specifically to attract pollinators. It connects a college campus with an urban forest, in an effort to support movement of small pollinators, who often can only fly short distances at a time. Through Sarah’s effort, the owners of these tiny flowered plots collaborated to create something greater than the sum of its parts.


Photo credit: Matt Ziatunich

Here in San Francisco we have the Green Hairstreak Corridor, a series of small habitats in the Inner Sunset, intentionally designed to support the Coastal Green Hairstreak butterfly. This Nature in the City project focuses on the single butterfly species, but with the same goal as the Pollinator Pathway of providing a series of habitats that support insect movement, rather than a single oasis of appropriate flowers. This type of effort is inspiring in its ability to bring neighbors together toward a goal that goes beyond the beauty of their individual outdoor spaces.

Our gardens as part of the urban landscape

By Lauren Lewis

Cities exist in their particular locations because at the time of their formation the location itself offered something vital for their earliest inhabitants. Space to build shelter on, trees to build with, wildlife to eat, and above all: water. At a city’s inception city dwellers depended on these features of their environment for their lives and livelihoods, and if the features weren’t robust enough to support a growing population, a city wouldn’t form in that spot.

Do we still depend on these features? In a purely survival sense we do not. As San Franciscans we use water from the Sierras, our food comes from the Central Valley and beyond, our building materials are sourced planet-wide. But we do depend on these natural features for livability and identity of the city. Many of our neighborhoods, which give us a sense of home within the large urban landscape, are defined by geographic features, most notably hills and valleys. And certainly our open spaces big and small and all the benefits they offer us, are dependent on natural elements. Our open spaces, from our patio gardens to our regular walking routes down the Panhandle, connect us to the natural elements that have shaped life in the city for every single San Franciscan.

Version 2San Franciscans are very familiar with the city’s hills. We know the hills by the vistas they provide and the varying strenuousness of our daily walks, but what’s normally hidden from view is how the hills determine water flow below our sidewalks. Arroyo Dolores and Old Arroyo Dolores used to flow eastward down our current 18th and 14th streets to where they joined up into Mission Creek, around the north side of Potrero Hill and out to the bay. The east Mission neighborhood is low lying and was likely marshy in the past, and now when we’re lucky enough to get a heavy rain, there can be serious flooding on Folsom St.

What this means for us at Small Spot Gardens is that we are powerfully guided in our design and plant choices by the water that has historically flowed or avoided the ground under your particular space. When starting a new garden project we can refer to maps of old San Francisco (for example to predict whether plants in the garden are likely to reach underground water with any ease. When we choose plants with this in mind we’re tying your garden into the space and history that surrounds it.

Old blog

Once upon a time we had a blog here and it was a little different from what we’re doing now. Might be fun to glance at but we’re focusing more on the nature – city connection now 🙂 All the old posts are below.