Environmental Center in August - Oakland
It’s a great privilege to work and farm two gardens; my own garden on my own home property, Poppy Corners, in Walnut Creek, and my school garden, behind the Environmental Center at Merritt College, in Oakland.
In some ways, these two gardens are very much the same. They were both conceived and begun by the same gardener - me. I have a certain gardening aesthetic, which you’ll find reflected in both spaces; I have a certain way of doing things that works well for me, and I use those methods in both gardens.
However, there are a lot of differences, too. I’ve been working in my home garden for nearly 19 years, while the school garden was started in January 2022. My home garden’s design, planting, and maintenance are largely done by me, with a little assist from Tom once in awhile, while the school garden is designed, planted, and maintained by a whole host of folks, mainly students, a new group of which arrives each semester. Each garden has been built using what materials could be found or purchased at the time, and the landscapes reflect that. The soils are different: In Walnut Creek, we have 100% clay, because this land was under water a long time ago; the school garden is on top of a hill which is uplifted volcanic matter that has greatly eroded, which gives it a rocky, sandy texture. (*Note - in both gardens I grow annual vegetables in soil that is brought in, because neither original soil is great for growing veg.) The goals for my home garden are to provide food for my family, habitat for wildlife, and beauty for the neighborhood. The goals for the school garden are to provide a safe learning space and a lovely place for students to gather; this forms community, which our program is determined to provide.
But another main difference between the two spaces is climate.
Walnut Creek is about 20 miles inland from San Francisco and its bay. It has mountains surrounding it to the east and west, while to the north and south are long valleys. Oakland is directly on the bay, about 10 miles east of San Francisco. Oakland runs from the flats in the west, up into the hills to the east; this divides the city in many negative ways, while also dividing it climatically. My school, as I mentioned, is in the hills.
Why does this matter, you might ask? We all have climate differences depending on where we live, but here in the Bay Area, we have far more differences than most, thanks to the influence of the San Francisco Bay and the Pacific Ocean. We call these ‘microclimates.’ I’ll get to those in a minute.
But first, this is the USDA Plant Hardiness Map. This map was developed primarily as a tool for farmers, but gardeners use it frequently as well. These zones are divided by the lowest temperatures rather than the highest; for instance you can see that the central northern part of our country gets quite cold in winter, while the southern part of the country stays warm (or at least temperate) in winter. If you look at this map, and the close-up below, it looks like the Bay Area (about a third of the way down the state from Oregon) is generally homogenous. That is, that the coldest temperatures in San Francisco are about the same as the coldest temperatures in Antioch. There are some slight differences, but it’s not markedly different. According to the USDA, Poppy Corners is in Zone 9b, which gets down to a low of 25 degrees, while the Environmental Center is in Zone 10a, which can get down to 30 degrees.
Not a lot of difference, according to the lowest temps.
Those lows are extreme examples, of course - they are what ‘might’ happen, while the lows over time are not nearly that low. I have found that wintertime in Walnut Creek includes a few nights under 30, while most of the time we are in the upper 30s to low 40s. In Oakland, the low rarely gets below 50, as is more usually around 55 at night.
The USDA doesn’t take in to account the high temperatures during the day, which are also quite different. For instance, summers at Poppy Corners generally involve regular daytime temps in the 90s, with many days over 100. Summers at the Environmental Center are much more temperate, and generally stay in the high 60s to the mid 70s.
Here’s another difference: The humidity in each place varies greatly. Walnut Creek rarely gets summer fog from the bay - we’re just too far inland and the fog has to make its way over the Berkeley hills to get to us. But we do tend to get ‘tule’ fog in winter, which is moisture creeping in from the Sacramento/San Joaquin river delta to our east. However, Oakland regularly gets fog in the summer, as it’s much closer to the bay. In fact there are many mornings when I arrive at work in the summer to find the path soaked by fog drip. And in winter, Oakland does not get the tule fog. All of these things determine what and how you grow plants, and the differences can get a little frustrating.
Long ago, it became clear that Bay Area gardeners needed some guidance; growing things in San Francisco was obviously not the same as growing them in San Jose, or Mill Valley, or Richmond, or Vacaville. Gardeners clamored for more specific zones, and in 1954, a local magazine called Sunset published a book called The Western Garden Book, which redefined the climate zones and in turn, local horticulture. The Western Garden Book was, and still is, considered the bible of western gardening. Many gardeners use solely the Sunset zones (17 of them across the west) to plan and plant their gardens.
The Sunset climate zones take in to account all of the things I mentioned above: Not just the wintertime low temps, but also the summertime highs, and the humidity, and even the elevation. On this map, you can see that my garden in Oakland is in zone 16, while my garden in Walnut Creek is in zone 14. The descriptions Sunset gives for each zone is great, but here’s what I think is the most salient point: The coastal climate of Oakland is dominated by the ocean weather about 85% of the time, and by inland weather about 15% of the time, while the inland valleys in Walnut Creek are the opposite.
On top of that, as an observant person, I have discovered that there are micro-climates within microclimates. Poppy Corners, being in the deep valley on the west side of Mount Diablo, tends to get even more extreme temperatures, because the air is trapped by the mountain. Our winter temps are lower, and our summer temps are higher, than other cities in zone 14. We know this because we have recorded it for several years on our weather station. Here’s another interesting and salient fact: In the Bay Area, it cools down at night. It very rarely stays warm, no matter how high the temperature gets during the day.
“Ok,” you might be asking, “so what does all this have to do with actual growing in each garden? What’s your point, Elizabeth?” Why am I obsessively pondering this climate-zone stuff?
Here’s why: Everything in the school garden grows better.
Now, the school garden is not as mature; the perennials haven’t been there as long, and haven’t had as much time to grow. The space is changing all the time, as we determine what the needs of our classes/desires of all the instructors are. These things are reflected in the appearance of the garden. But even still - I look at the vegetables and flowers and herbs and natives and fruit trees and I think, damn. Oakland’s got it going on.
This is counter-intuitive. You’d think that the higher heat of my inland garden would be better for summer veg, at least. Tomatoes and peppers like it hot, right? And you’d think that the inland winter chill would be better for fruit, right? And at one time, maybe that was true - maybe the differences wouldn’t have been so marked, 50 years ago. Just little things, little tweaks here and there, would help the gardeners in different zones to make subtle changes that gave them success.
But in our changing climate, we already know that the extremes are getting more extreme. In my Walnut Creek garden in the summer, I either have full sun which bakes everything to an absolute crisp, or I have partially shady conditions that sure, don’t burn the plants, but also don’t allow for maximum production. In the Oakland garden in the summer, there is full sun nearly all day - but the plants don’t burn, and the fruit and veg ripens spectacularly. Take this example of the tomatoes in each garden:
Poppy Corners - spindly and not a lot of fruits
Environmental Center - chubby and huge, and full of large as-of-yet-unripe fruits
Why is this? Here’s my theory: It’s all about the range of temperatures. In Walnut Creek, in the course of a year, we range from 25 degrees to 115. That’s not too different than many places in the United States. But, over the course of a summer day, we often range from 50 degrees to 100. A difference of 50 degrees is not unusual here. That’s a HUGE daily change. In Oakland? Over the course of a year, it ranges from about 40-80 degrees. Much less of a range than most places in the United States. And over the course of a summer day? Mainly about 65-75 degrees. Not a very large daily change.
And this, my friends, is the big difference in my two gardens. In a study on Elsevier called “Ambient Temperature Signalling in Plants,” the introduction states, “Plants are exposed to daily and seasonal fluctuations in temperature. Within the ‘ambient’ temperature range… temperature differences have large effects on plant growth and development, disease resistance pathways and the circadian clock without activating temperature stress pathways.”
Plants are adapted to yearly, monthly, daily, and hourly temperature ranges. What they are NOT adapted to is increased temperature stress. And it is extremely clear to me that we are experiencing increased temperature stress at Poppy Corners. What I could grow easily 15 years ago, or even 10 years ago, I cannot grow now. And for now, at least, Oakland’s extremes are mostly mitigated by the beautiful San Francisco Bay. THAT is why everything grows better at the Environmental Center. And it’s why we, as gardeners, have to be aware of what’s happening in our own plots in our own cities, and why we have to learn to adapt to how conditions are now, not how they were when we started.