Guest Speaking Event

I know I have not checked in here for quite awhile; I keep meaning to write, but my work schedule has been unremitting. I promise that the spirit is willing even if the workload is not, and perhaps soon I will be able to share some cool new garden thing with you. For instance, something about all the cool bird boxes Tom has been working on… and did you know that house finches eat the blossoms of manzanitas for pollen and nectar???

For now, though, you might be interested in joining a zoom talk I’m giving on Tuesday, January 30, at 4 pm (California time), for our college design forum. The subject is ‘Intensive Food Production for Urban Spaces.’ I’d love to have you join in; the link is below.

(By the way, if you’ve been in my classes, particularly Edible Landscaping, this is all material you’ve heard before so you’ll probably want to skip it.)

Hope to see you there!

Here’s where to join.

Road Trip

*Note from Elizabeth: Tom is posting today!

We've been driving electric cars for a number of years. When our trusty Mazda Protege 5 that we purchased after Adam was born finally got too old to properly maintain, we first looked at hybrids, but then settled on the first of a series of Chevy Bolts that have come under our care. We leased a couple of different Bolts between 2017 and 2020, and purchased our current Bolt in 2020. In all that time, we had never taken a trip that would require stopping to charge the car part-way through the trip. The Bolts have been very capable of handling our normal usage – commuting to Oakland and San Francisco, ranging out for hikes across the East Bay and North Bay – with overnight charging from our garage outlet. I think the longest drive I ever took was a drive to Sacramento and back, a round trip of 120 miles or so, well within the capability of the Bolt. Any longer drives we've taken (to Southern California or our trip last July to Lassen National Park) have been with our gas-powered Honda Pilot.

Paprika, our 2020 Chevy Bolt

This changed last weekend when we decided to drive down to San Luis Obispo to visit Adam at Cal Poly. The drive from our house to SLO is about 230 miles, right at the upper end of the Bolt's range. We didn't want to chance it, and so planned a stop on the way down in King City, about 170 miles from the house, where there are a few fast chargers on the EVgo network, something we got an account for when we got our first Bolt but haven't used in years (we're on the freebie "just pay us when you use it" plan).

The drive to King City was fine - a little more traffic than we expected, but nothing horrible. We arrived, found all of the chargers to be available, and plugged in with the car registering about a 44% charge. We found a little coffee shop around the corner and settled in to a nice iced coffee. Within 30 minutes the car was charged up to 80%, but without firm plans for charging once we got to SLO (we were spying another EVgo station near a supermarket), we went ahead and let the car charge for the full 60 minute limit EVgo puts on a charging session, getting us up to about an 87% charge before proceeding to SLO.

As it turned out, the hotel we stayed at had a couple of lower-speed charging stations, so that solved our SLO charging needs. We plugged in there (downloading another app to do it, EV Connect) and got back up to a full charge as we slept.

On the way back we initially planned to stop in Gilroy at another EVgo station, but as we arrived, two other cars had just pulled in to the stations that were showing as available on the app. We drove on about another 10 miles to Morgan Hill and found an open spot there (the last open spot of a bank of four chargers). Another iced coffee at a nearby spot; this time we only had it charge about 45 minutes, getting us from around a 30% charge up to about 75% before we unplugged and moved on, knowing that we'd be able to just plug in at home upon our arrival.

All told, a very successful trip! The stops we had to make to charge, while certainly longer than the five minutes you'd spend filling a tank with gas, didn't seem overly burdensome. Elizabeth and I are still doing intermittent fasting, but if we were lunch-eating people, these stops would have fit in perfectly with a stop for lunch. That said, the charging station at the hotel was an unexpected and pleasant surprise. Also, had we been on a longer car trip (say, down to LA, 360 miles away), we likely would have wanted to make two charging stops along the way, unless we had a guarantee of some kind of overnight charging once we got there.

Now for some engineering, economics, and environmental impacts.

Charging speed. Our 2020 Chevy Bolt has a battery that can store a total of 66 kiloWatt-hours (kWh) of charge, and a maximum charging speed of 55 kilowatts (kW). One might think that you'd be able to just divide – 66 kWh capacity ÷ 55 kW charging speed = 1.2 hours = charge from 0% to 100% in an hour and 12 minutes – but that's not the case. In order to promote longer battery life, electric car charging rates are modulated during the charge, going at a higher rate when the battery is at a low percentage but then tapering off as it gets closer to 100%. The EVgo app shows a cool graph of charging speed while you're charging so that you can see how it's going:

The Bolt's 55kW max charging rate is on the low end of electric car charging rates, as is the 66kWh battery capacity. For comparison, the Kia EV6 long-range model has a larger battery capacity (77.4 kWh) and a much higher maximum charging rate (233 kWh); the Ford F-150 electric extended range has a 131 kWh capacity and a charging rate of 155 kWh. How those larger batteries translate into range will, of course, vary with the weight of the vehicle and how you're driving it, but the faster max charging rates means that you can charge up much more quickly using one of the fast chargers, so long as you can find one that'll support the faster charging rate. The EVgo location in Morgan Hill had four fast chargers, but two of those four are limited to 100 kW, so even though a car could charge more quickly, you're then limited by the charger itself.

Economics: All told, we put about 470 miles on the car with this trip, using 130.16 kWh of electricity, which works out to about 3.6 miles per kWh. The charging sessions we did on the road and at the hotel cost us $43.65; we also charged again once we arrived home to get us back up to the full "tank" that we had when we set out. That charge (at our current off-peak overnight PG&E rate of about $0.40 per kWh) will cost us $14.08, so our total electricity cost was $57.73. Most of the gas stations we saw on the trip were charging about $5.50 per gallon of 87 unleaded, so that same $57.73 would have gotten us about 10.5 gallons of gas, putting our equivalent fuel efficiency just under 45 miles to the gallon. Not too shabby.

Carbon: Some rough math – in 2021, PG&E said that they're emitting 89 pounds of CO2 per MWh of electricity, so the 130.16 kWh of electricity we used for this trip put about 11.6 pounds of CO2 into the air. Had we burned the 10.5 gallons of gas noted above (at that really efficient 45 mpg equivalent), we would have released 210 pounds of carbon into the atmosphere. Taking that same trip in our Honda Pilot, which gets about 24 mpg on the highway, we would have used about 19.6 gallons of gas, releasing 392 pounds of CO2. Now, PG&E's electric power mix is very carbon-friendly – 50% renewable, 39% nuclear, 4% large hydro, and only 7% natural gas – resulting in a CO2 rate that's an order of magnitude below the national average, but even if we were charging in Texas (where electricity generation emits 856 pounds of CO2 per MWh), our electric car trip would have emitted 111 pounds of CO2, which is still half of what our theoretical super-efficient 45 mpg gas car would emit.

As I mentioned earlier, this trip to SLO turned out to be very successful, and it's opened up some possibilities that we might not have considered before. It also shows the work to be done, mostly on the availability of public charging stations. California has 14,000 public charging stations, which is a lot (the other 49 states combined have 37,000 public stations). The availability of public stations is important not just for those taking long trips, but also for people who don't have the luxury we have of plugging in the car overnight at the house. California committed to phasing out the sale of new gasoline-powered cars by 2035, which in some ways is right around the corner, but it seems eminently doable. With transportation making up 28% of the country's CO2 emissions, taking bold steps to lowering the CO2 emissions is an important component of our work to mitigate climate change.

Leveling the Hive

When we installed our top bar bee hive (made by my father) ten years ago, we picked a nice site in a place that got morning sun and afternoon shade, was sheltered from wind, and mostly hidden to passersby. We also leveled the site before putting the sawhorses and hive in place, resting them on concrete blocks to keep the legs up off the soil.

Over the years, the earth has settled and shifted. This is due to many factors: One, this is earthquake country; two, we have 100% clay soil which swells and shrinks during wet or dry periods (and in California, it’s either very wet or very dry, not much in between); and three, I’ve been adding mulch in that area for years, which has probably worked its way under the legs somehow. So it’s not a surprise that our hive began to list.

For a long time, we would ‘solve’ this problem by shimming up a side (you can see our first shim on the left). That was an easy ‘fix,’ and would hold for a while before needing to shim it up on the other side. Sometimes I would even put an especially large piece of bark under one of the sawhorse legs. It wasn’t an exact science, but the thought of moving the whole thing and re-doing the area was daunting.

But finally, this fall, the hive started to lean in earnest. This was worrying, not least because if it started to gain some momentum, the whole thing could have just slid off the sawhorses, which would have been a colossal mess and would probably really freak out the bees (and make them very aggressive and/or want to leave), or even harm them. Was it leaning over that far? Probably not, probably I’m exaggerating. But what was definitely happening was that our bees started to beard every night, even on cool nights.

Bearding is when bees hang out at the front of the hive, on the ‘front porch’ so to speak, and make a big hanging mass of bodies which looks like a beard on the hive. This usually only happens when it’s super hot out, and the bees can’t keep the hive at the 93 degrees they prefer. They remove some heat from the hive by removing bodies. Smart, right? But bees can also beard when they run out of room, or if there is poor ventilation in the hive.

See the picture at the top of this post? That’s a beautiful comb, from our top bar hive. Since top bars don’t use frames, like Langstroth hives, the bees build on a bar which rests on the top (hence the name). What this allows is for the bees to build the way they like. And bees like to build their comb in catenary curves. When the hive is level, the comb perfectly fits the shape of the hive box, allowing for something called ‘bee space,’ which means there’s just enough room at the edges and bottom for the bees to move freely around the colony.

Gravity plays a big role in how bees build comb; they naturally build in line with the pull of gravity. When a hive is level, they create an ideal comb. When a hive isn’t level, the bees are confused. They build asymmetrically or in a funky shape. The comb can encroach on other combs, and create a mess. It can also lean with the hive, and honey is heavy, so the comb can slide off the top bar and create an enormous sticky pile of wax, honey, and bees at the bottom of the hive.

My working theory, while viewing the leaning hive, and the constant bearding, and after hearing how Tom, when working in the hive, found lots of comb stuck to the sides and bottom (so the bees weren’t building comb correctly), was that the unevenness of the hive was past the point where a shim would help. We just needed to redo the entire area. This was a bummer, because it meant we had to move the hive.

Just like there’s an ideal time to work inside a hive (sunny warm afternoons, when a good portion of the bees are out foraging), there’s an ideal time to move a hive, and that time is never. But, second best is when it’s dark and the bees are tucked in for the night. So, since I’m not allowed to work anywhere near the hive due to my allergies, we recruited my dad to help.

Mom and Dad came over for dinner, and once it was dark, Tom and Dad went out to the hive and discussed the operation. Tom brought out our other sawhorses and set them nearby. They both made sure to cover arms and legs securely to avoid stings. Mom went out with a flashlight to help light the scene. And then there was nothing for it but to move it, that heavy hive, over to the side several feet. Job done! And no one stung, and no fuss from the bees at all.

I checked on them periodically the next day, and they were very confused. But by the second day, they had a new pattern of exiting/entering all figured out.

Then, the following weekend, the real work began. Tom started by removing eight inches of mulch and leaves until he found bare ground. Then he bought 240 pounds of construction-grade sand and wheelbarrowed it over to the space. Wet, level, wet again, level again, rinse, repeat. Then he bought bigger concrete footings and set them in. Level, pound, level again, pound again, rinse, repeat. Finally the sawhorses went back on the blocks. And then, my dad had to be pressed into service for the second time (will work for cookies!) and helped move the hive back in place in the dead of night. And voila! A newly leveled hive.

The bees had absolutely no confusion the day after moving back, which was interesting. They must have good memories. Or deep instincts that reminded them that they oriented to this position originally.

So, that oughta do us for another ten years. Unless the big one comes, and then we’ll have other things to worry about anyway.

Foliar Feeding - Does it Work?

In the past couple of weeks, I have toured several different farms and gardens where the caretaker sung the praises of foliar feeding. “The plants absorb the nutrients so much faster and growth just explodes!” said one farmer enthusiastically. Every time I hear a comment or recommendation regarding foliar feeding, my inner bullshit alarm goes off. I just don’t believe it actually works. But is my hunch true, or am I just stuck in old thinking?

Years ago, I was enamored with the idea of making compost tea and then spraying it as a foliar feed on my veg and fruits. I was sure it would improve the health of my plants, deter pests, and increase yields. Making compost tea is a lot of work; it requires a bubbler in order to oxygenate the mixture as it’s steeping, keeping the organic matter in a mesh bag so it doesn’t clog the bubbler, then decanting the mixture into a sprayer, etc etc etc. And then the spraying itself, messy and time-consuming. All of this has associated costs, too - you need to buy a big sprayer, a bubbler and tubing, several containers to hold everything, and mesh bags or cheesecloth. This is all after the regular work of making compost, which is noble and important but not exactly a hands-off project. After all this fuss, I really didn’t notice much of a difference in my plants when I performed foliar feeding.

Not long after, I took a Plant Nutrition class as part of my ‘nursery management’ coursework at Merritt. Several students were convinced that foliar feeding worked better for plant nutrition than any other method. My instructor was dubious. She explained that leaves are not designed to take in nutrients. There are nearly microscopic holes on the bottoms of leaves, called ‘stomata,’ which evolved to provide gas exchange - these holes allow for oxygen and carbon dioxide to move between the plant and air as part of the process of photosynthesis. They can expel water, but actually repel water that’s trying to come in, using a waxy coating for that purpose.

More recent research has revealed the existence of micro-pores on the surface of leaves, and they are lined with negative charges which attract positively charged cations (things like calcium, magnesium, and potassium). This research has shown that nutrients can enter these pores as ions in water, but sprayed leaves dry very quickly and limit much absorption, and only about 15% of the nutrients applied this way are absorbed.

And as my professor then told us, even if leaves do take in nutrients in this way, the plant is really not designed to move nutrients other than sugars from the leaves to the roots, or to any other part of the plant. The whole system is designed to draw nutrients from the soil solution (a pool of available water at the rhizosphere that contains nutrients) up through the roots and into the xylem, which is a kind of fluid river that moves water-soluble nutrients from the roots to the rest of the plant. There’s a downward river, too - the phloem - but it’s carrying sugars made in the photosynthetic process down from the leaves to the root zone. That’s what it’s designed to do, not carry nutrients from the stomata down to the roots. So even if nutrients are entering the leaves, they are stuck in the leaves. They are immobile due to that stronger positive charge.

Let’s take calcium for instance. A gardener recently told my class that she sprayed her tomatoes using a foliar feed of liquid calcium to prevent blossom end rot. But calcium will not move from the leaves to the fruit. It can only move from the roots to the fruit. Tomatoes also do not absorb calcium through the skin. So this is arguably not helping the plant avoid blossom end rot. (And if you’re a long-time reader of this blog, you already know that blossom end rot is not really a calcium issue.)

Remember my plant nutrition class? My professor posited that what was really happening in foliar feeding was that the nutrients were dripping off the plant and down into the soil, thereby entering the soil solution. But she was not married to that theory and was game to experiment. So, in lab, we planted a bunch of leafy vegetables in 4” pots. Then we covered the whole surface of the soil with plastic wrap. Then we turned the plant on its side and sprayed the leaves with a foliar feed (I can’t remember what the actual fertilizer was, unfortunately). This way the feed dripped off the leaves onto the ground, instead of down into the pot. And the plastic wrap was there as insurance to make sure that nothing entered the soil. We let the plants drip dry before righting them, removing the wrap, and watering them with plain water before replacing the wrap. We cared for these plants over the course of the whole semester.

Care to guess the result? The plants in 4” pots with only foliar feed did very poorly indeed. They were yellowed, diseased, and wilted. We concluded that foliar feeding didn’t work, or at least it didn’t work well enough to supply enough nutrients to the plant.

But that’s not a rigorous study, so I consulted some other recent research. According to a 2016 study by the University of Wisconsin-Madison’s Agriculture Department, “for many nutrients, there is little or no published information showing a valid relationship between crop yield increase and tissue nutrient concentration that provides good reason for making widespread recommendations to apply a foliar- or soil-applied fertilizer that includes that nutrient,” and, “for many of these essential nutrients, we lack proven research that defines the exact minimum nutrient concentration below which yield is harmed and verifies that a beneficial yield response to foliar feeding occurs.” And according to a 2020 article from Ohio State University’s College of Food, Agriculture, and Environmental Services program, “results (in foliar feeding) were inconsistent and didn’t reveal a cohesive pattern of increased yield or… plant health for the sites in this study.”

I suppose it’s possible that spraying the leaves with a nice compost tea might help protect the leaves from some fungal infections, or pest predation. But as a method of actually feeding the plant, I think it’s an inferior choice. The best thing to do for any plant is to provide it with plenty of organic matter, which allows the soil biology to process all the nutrients in the organic matter and make them available in soil solution for the plant roots.

Reference: “Why I Typically Do Not Recommend Foliar Fertilization,” by Caleb P. Goossen, Ph.D, MOFGA Crop Specialist, June 2023.

Mast Year

We have an enormous Valley Oak (Quercus lobata) in our driveway garden. It’s in a very inconvenient place, right on the edge of the driveway, and because of that you’d think its growth would be compromised. Fully half of its root system is compacted by concrete and parked cars. This isn’t good for any tree, and definitely not for Valley Oaks, which usually grow in grasslands and oak woodlands. But this tree was planted many years ago by a squirrel and the previous owners of this house never pulled it out, so it’s grown into the space and is extremely healthy. Valley Oaks can also take some irrigation (they like wet crevices and canyons in the wild) and this one gets that, being surrounded by chosen landscaping. Every year I have my tree guy come out and look at it, and usually it just gets a trim every couple of years. This year, the tree guy was worried about its split trunk (this compromises the strength of the canopy), and so we will be installing cables to decrease the chances of a total split. But anyway, that’s not what I wanted to write about today. No, I wanted to write about the acorns.

We are having a mast year. A mast year is marked by a lot, and I mean a LOT, of acorns. All oaks mast, and in fact many plants mast, which just means they produce a lot of seed in any particular year. Sometimes ithis masting happens every year, sometimes every other year, sometimes two years in a row and then not again for 20 years, there is really no way to tell if it’s going to be a mast year. In the case of this particular Valley Oak, our last mast was three years ago, and frankly, I didn’t expect another one so soon. What makes it an especially interesting natural process is that no one really knows why masting happens.

This is how it looks every single morning - a new carpet every day.

Masting is a great mystery, but an even greater mystery is that all the trees of the species, within a very large geographical area, all mast at the same time. Thinking about that will really twist your noodle. How do they all know to do it at once? And why do they mast in the first place?

Well, there’s lots of theories, and they all make sense. One theory is that mast seeding is for predator satiation. When a population of plants produces seeds in unusual amounts, their predators will never be able to eat them all, leaving some to germinate and produce the next generation of plants. Another theory is about pollen coupling. This is a concern in the timing of flowering in pollinating species - the flowers need to sync with one another in order to cross pollinate. If all individuals in a population flower at the same time, more flowers will be pollinated, leading to increased seed production. But it’s expensive to make a lot of flowers, and plants have to have enough resources to do that. This explains why trees might mast following wet years - more water means more resources, means more flowers, means more seed. But some folks think that trees mast following drought years, as a ‘last gasp’ effort to produce offspring. Resource budgeting is another possible explanation. Plants need energy to produce seed, and they also need energy just for growing. Which do they concentrate on in any given year? In theory, if all plants in a large population are experiencing a similar amount of resources, they will either grow or flower similarly. Or maybe it’s about resource storage, and the trees are ‘saving’ resources for many years until they are ready to produce a great amount of seed. Environmental cues also result in hormonal responses in plants, so masting may have nothing to do with resources or pollination at all. Of course we also can’t leave out the possibility that the trees are ‘talking’ to each other, communicating through underground fungal networks. Other species have been shown to do this, so it’s no great leap to imagine that oaks do this too.

Whatever the reason (and maybe some things will just never be explained, and how lovely is that? that we can still be mystified by nature), what it means for me personally is lots of sweeping and shoveling into the green bin. During our last mast year, I left a lot of the acorns where they lay, and I’m still pulling out oak seedlings. One big Valley Oak is enough, thank you, so I’m collecting as many as I can this year.

Meanwhile, many times every evening, sitting on the couch watching TV, Tom and I jump when a particularly hefty acorn lands on the roof of the chicken coop, producing a loud BANG. I wonder if the chickens are sleeping at all.