I Grew Tomatoes With the Heat From My Crypto-Mining PC

Anything worth engineering is worth overengineering

Images courtesy of the author.

If you spend time on Instagram in our post-pandemic world, you’re probably experiencing some gardening FOMO. Maybe your biggest lockdown goal was “pwn Candy Crush” or, if you’re like me, “limit your toddler’s screen time to a scant five hours per day.” Now that we’re months into the pandemic, though, your friends who channeled their early quarantine angst into planting seeds are likely starting to reap the benefits in terms of fresh herbs and handfuls of juicy, Insta-friendly heirloom tomatoes.

If you’re more comfortable with wires and while loops than bugs and compost, don’t despair. Gardening has become increasingly tech-enabled. There are now tons of ways that you can apply emerging technologies to the challenge of growing your own food.

Just before Covid-19 struck, I started a project to build the world’s most overengineered, high-tech garden. It ended up incorporating hydroponics, solar power, cryptocurrency mining, recycled water, sensors, the Internet of Things, infrared imaging, and much else. Here’s how I did it — and how you can build your own tech-enabled pandemic garden, too.

I should say this clearly from the get-go: I kill plants. Even succulents, which can go weeks with no care at all, are too much for me. People often give these to me as gifts, and I’ve managed to keep exactly three of them alive. This is surprising, as I come from a long line of gardeners — my father is an avid gardener, as was my maternal grandmother. But apparently this inclination — and the corresponding skill — skipped at least a few generations.

It was a dilemma, then, when I discovered that my three-year-old has a passion for gardening. We got him some plants last summer, and he diligently watered them every day, growing a handful of tomatoes and a lovely calla lily on our back patio. Mornings began with at least five minutes of “plant time,” spent checking his plants, fertilizing, pollinating flowers with a toothbrush, and performing other gardening functions that are alien to me. Obviously, we wanted to encourage that interest. But again, none of that is in my wheelhouse.

As the founder of an A.I. company and the owner of a DIY-tech YouTube channel, though, gadgets, green tech, sensing, and the like most definitely are. In late 2019, I hatched an idea of creating an indoor sustainable garden by applying as many technologies and gadgets as I could think of. I wrote up my musings about the idea in January of this year. Then I figured what the hell, dove in, and actually built it.

Right from the start, I knew I didn’t want to mess around with soil. For one thing, it’s yucky. It’s also mysterious. As The Atlantic shares in a detailed article about soil, the stuff is teeming with bacteria, archaea, microbes, and fungi — as well as bugs, earthworms, and other beneficial creatures — that work together in a complex synergy to keep plants healthy. As The Atlantic reports, a single teaspoon of good soil can contain 10,000 to 50,000 different species of “protozoa, nematodes, mites, and microarthropods” and “more microbes than there are people on the earth.”

That felt way too complex to me. Wanting to abstract much of that away, I turned to a technology that has existed for thousands of years and is enjoying a tech-enabled resurgence: hydroponics. Hydroponics is the science of growing plants in water. Instead of placing them in soil, you bathe your plants’ roots in flowing water. You then add the basic nutrients they need to that water, instead of providing them via soil.

The benefits are numerous. Compared to traditional gardening, hydroponics can allow for up to a 90% reduction in water use, much higher yields, and up to two times faster growth rates. Because the water in a hydroponic system continually recirculates, there’s also no need to worry about watering plants consistently, you can control and eliminate fertilizer runoff, and you can grow plants indoors, in a tiny space.

This last part was important to me, as I wanted to set up my high-tech garden in my garage. The San Francisco Bay Area, where I live, enjoys long outdoor growing seasons and little danger of frost, but I wanted to demonstrate that one can create a viable high-tech garden in any space: a basement, an unfinished room or shed, the balcony of a rented apartment, etc. Hydroponics allows you to grow meaningful amounts of produce in small spaces — including indoor spaces with little to no natural light — so it felt like a fit for that reason, too.

When I first started my project, I expected to have to build a small hydroponics system from scratch. But I quickly discovered that someone had done that for me. AeroGarden — a division of the well-known garden supply company Miracle-Gro — sells a variety of premade hydroponic gardens. These range in size from the diminutive Sprout (which retails for $76.99 and grows a handful of herbs table-side) to the $895 Farm 24XL, which grows 24 plants and includes advanced features like a programmable day/night cycle and Alexa voice control.

Choosing a new type of plant to grow feels a bit like importing a Python module or installing a new graphics card.

All AeroGarden models (and, fundamentally, all hydroponic systems) include a few basic components. There’s a water-filled tray to hold your plants, a small pump to circulate water over their roots, and a set of LED grow lights that provide the illumination your plants need to thrive, even in an otherwise dark room.

AeroGarden sells its plants as “pods,” which include seeds and a porous support material inside a plastic tube that you snap into your garden. Larger garden models accommodate more pods. You can mix and match many pods within a single garden, allowing you to grow several kinds of plants at once. AeroGarden offers a dizzying array of premade pods, from spring flowers to ghost peppers. It also offers a grow-anything kit, which allows you to create your own pods and grow nearly anything in your AeroGarden. (To preempt an obvious question, yes, you can grow pot in it.)

I love the modular aspect of AeroGarden’s pods. For someone used to the conventions of the tech world, it’s very familiar. Choosing a new type of plant to grow feels a bit like importing a Python module or installing a new graphics card. You browse through a list of options, make a choice based on a set of capabilities or features that you want to access, and then plug the new module into your project.

I bought two AeroGarden Harvests — a midrange model that costs around $110 and accommodates six pods each. I also picked up a set of heirloom cherry tomato pods and a set of pods for assorted herbs. My son and I set up the AeroGardens in the garage and installed the pods. By the time we got them up and running, it was mid-February.

AeroGardens are primarily designed for indoor use in a climate-controlled room. My garage isn’t climate controlled. California has mild weather, but it still gets chilly at night. In February, daytime temperatures are usually around 60 degrees Fahrenheit and dip into the 40s after sundown. Tomatoes grow best with a daytime temperature of 70 to 85 and a nighttime temperature above 60, so this didn’t seem optimal. I knew we would need some kind of heat.

We started by getting an Educational Insights tabletop greenhouse ($43 on Amazon) to hold the AeroGardens. This helped a bit with temperature—and kept the tomatoes nice and humid—but it still wasn’t ideal. To bump up the temperature and our tomato yield, I had an idea: Why not heat the greenhouse with the waste heat from a cryptocurrency-mining computer?

Cryptocurrency has exploded in prominence and impact over the past several years. According to industry publication Coin Telegraph, the market for mining hardware (used to create new cryptocurrency coins) is set to grow by $2.8 billion between 2020 and 2024. All this growth comes at a very real cost. The mining of bitcoin alone is estimated to consume up to half of all the electricity used by all data centers worldwide. The bitcoin network currently uses as much electricity as the country of Colombia.

All this electricity ultimately turns into heat. Most of the time, that heat is wasted. But some cryptocurrency miners, seeing an opportunity, are putting waste heat to productive use. Ukrainian company Hotmine is developing crypto-powered hot-water heaters and furnaces for home use. Heatmine, a Canadian company, has experimented with using crypto waste heat in homes in Quebec, which has frigid winters. And as of 2018, a Czech company was experimenting with “cryptomatoes” using heat from bitcoin mining to heat tomato greenhouses.

I’ve experimented with heating my home using cryptocurrency-mining waste heat on a small scale, with a good deal of success. For that project (and a photo series on the cryptocurrency industry), I built my own mining rig. It uses a custom PC, a super-high-efficiency EVGA power supply, and an NVIDIA GeForce 1070 graphics card — a staple of cryptocurrency miners — to mine a variety of crypto coins using the automated software NiceHash.

Running at full blast, the PC also gets quite toasty. For my heating experiment, I calculated that my rig draws about 220 watts of electricity, putting out 716 BTUs of heat per hour. That’s about the output of a small space heater or one of those overhead heaters you see on restaurant patios. The rig, which cost around $600 to build, generates up to $0.76 in mining revenue per day — not remarkable, but enough to offset some of my heating costs when I used it indoors in the winter.

Piping 716 BTUs per hour directly into my tiny greenhouse, I calculated, would be way too much heat. My greenhouse is 24 cubic feet, so putting in all the heat from the cryptocurrency-mining computer would increase its temperature by around 40 degrees. Even in the dead of winter — with a nighttime temperature of 45 degrees — that would still push my tomatoes to their 85-degree limit. On warmer nights, it would risk roasting them on the vine.

Instead, I opened the side panel on the computer and connected it to the side of the greenhouse. Using a FLIR One infrared thermal camera, I determined that the NVIDIA 1070 heats up to around 110 degrees when mining. This radiates a nice amount of heat into the greenhouse, moderating its internal temperature without overdoing it.

The glowing green logo of the NVIDIA GeForce is visible inside my greenhouse.

I also found that just running the computer near the greenhouse kept my garage a bit warmer than normal. It’s like a high-tech version of the tried-and-true gardening practice of placing water bottles near your plants. The bottles heat up in the sun during the day and then radiate heat at night, protecting your plants from frost and helping them grow just a bit better.

With all the supplemental heat from my mining computer, I felt like I needed some kind of monitoring system for my garden. At first, I thought about building a DIY temperature monitor with a RaspberryPi. But in keeping with the modular concept of the project, I decided to use another solution: an industrial sensing system from Monnit.

Monnit sells a variety of sensor gateways, which you install in your facility and connect to the internet. Once you have a gateway installed, you can buy up to several hundred tiny sensors, which allow you to monitor everything from temperature to vibrations to whether someone is sitting in a chair.

Each sensor uses a coin cell battery that lasts about six months and transmits over a short-range wireless radio to the gateway. That means you can place the sensors anywhere you want in the space you’re trying to monitor. The gateway forwards the sensors’ data along to Monnit’s cloud, where you can log into a web interface and get a real-time read on conditions in your facility.

This is a system intended for commercial or industrial applications, so it’s not cheap. Monnit’s ethernet gateways run about $220, and each sensor costs around $50 to $80. But the system has rock-solid reliability and accuracy, and Monnit’s data storage and charting functions are top-notch. I also liked how the system could potentially scale to a commercial-size greenhouse. I don’t plan to scale up my tomato project to a commercial facility, but it’s good to know that the technologies I’m demonstrating in my tiny greenhouse could potentially be used in a real, full-sized indoor farm.

I’ve experimented with heating my home using cryptocurrency-mining waste heat on a small scale, with a good deal of success.

The final step for my garden was to add water. Hydroponic systems use dramatically less water than traditional planting methods; according to the National Park Service, they can use up to 1,000% less. But because the plants are immersed 24/7, water is a crucial part of the process of growing plants hydroponically.

AeroGarden recommends using distilled water with its gardens. This felt like a big hassle — and a potential generator of a ton of plastic waste. So I looked for another solution. Ideally, I wanted to use recycled water. On a trip to Israel in 2012, I saw tomatoes grown using recycled water in the Negev Desert. And closer to home, I did a photo series at CoCo San Sustainable Farm in the Bay Area, which uses recycled water from sanitation provider Central San to grow food for local schools. So I knew it could be done.

But I didn’t want to have to drive to a recycled-water pickup point every time I wanted to water my tomatoes, and the water provided there wouldn’t be distilled. Doing some research, I came up with a solution: I could use the condensation generated by my home air-conditioning system to irrigate my garden.

If you have central air and you’ve walked around outside your home in the summer, you may have seen a little tube or hose dribbling out a stream of water. You probably thought, “I hope that isn’t a problem,” and then went about your day. It’s not a problem — air-conditioning systems work in part by removing water vapor from the air in your home. All the water has to go somewhere. Most air-conditioning systems jettison it through a little tube into the ground in your backyard or, in some cases, directly into the sewer.

That’s a major wasted opportunity. While the water from an AC condensate drain isn’t safe to drink untreated, it tends — like distilled water — to be very low in mineral content. It’s also free, readily available, and otherwise wasted. Many big institutions take advantage of this source of eco-friendly water on a grand scale — Rice University, for example, captures 14 million gallons of water per year from its AC systems. I decided to try doing so at home.

In a series of experiments, I determined that my home AC system dumps about one gallon of condensate water per hour. That’s a lot of water. At first I thought about building a complex device to catch water from my AC unit using a marine bilge pump, external power supply, and tubing to pipe the water into my AeroGardens.

Instead, I settled for a clear plastic bucket, which I placed under the condensate drain in my backyard. AC condensate can contain Legionella bacteria, so ideally you should boil it or treat it with UV light, chlorine tablets, or ozone before using it and avoid using it in applications that create aerosols, like a sprinkler system. I settled for letting my buckets fill up, then placing them in the sun for several days before pouring the water into my AeroGardens. I can’t vouch for the safety of that technique, but I’ve been okay so far.

With all the pieces put together, I now had a system that used hydroponics and LED grow lights to nurture modular plant pods. The whole thing was contained in a tabletop greenhouse, kept at optimal growing temperatures 24/7 by cryptocurrency waste heat, monitored by industrial IoT sensors, and irrigated with recycled water. It was an ideal way to experiment with some of today’s most compelling green technologies.

Oh, and it produces tons of tasty tomatoes. With AeroGardens, your only real responsibility as a gardener is to keep each garden filled with water and add some liquid fertilizer every two weeks when a light on the garden turns red. You can also do some light pruning to increase the yield on your plants — if you don’t, they’ll grow so large that they overshoot the AeroGarden’s grow lights, and your tomato production will drop. My son and I watched as our tomatoes germinated and began to sprout right on schedule, about five days after we “planted” the tomato pods.

Our herbs started to shoot up even faster, with little sprouts emerging about two days after planting. Over the next several months, our plants grew aggressively. We got to experience the excitement of seeing our tiny tomato seedlings grow into giant, leggy plants with little yellow flowers, and ultimately green tomatoes, which rapidly turned red — and were perfect for plucking by tiny hands.

The tech aspects of the project have worked out surprisingly well. The Monnit sensor system beams in temperature readings every two hours, which I can access as a series of charts in a web interface. The cryptocurrency computer has done an admirable job of keeping things balmy. On a recent chilly night in September, when nighttime temperatures dropped into the 50s, our garden stayed at a comfortable 74 degrees. In the heat of the day, it got a few degrees above the ideal maximum temperature of 85 degrees, but the tomatoes seem fine.

Chart of temperatures in the greenhouse during a day and night in mid-September.

From our limited experiment, I’ve seen that hydroponics really do appear to deliver on its promise of faster growing times and bigger yields. Last summer, we labored for months to grow about 10 tomatoes and a handful of herbs in the backyard. With our high-tech garden, we got to watch as our herbs—the basil especially—started out by producing enough leaves to flavor a tomato sauce, then enough for a pesto, and finally so many that I had to cut them back almost daily, drying them or using them in infused olive oils to stop them from going to waste.

AeroGarden plants last about six months; during that time, you can harvest from them continually. Our herbs died back after their six-month growth window was over, but the tomatoes are still going strong. At times, we’ve been able to harvest tomatoes by the handful and have used them in everything from sandwiches to caprese salads to soups.

At the beginning of the project, I struggled with deciding what to grow. It takes about an acre of land to grow enough food to feed one person, so feeding our whole family with a hydroponic garden wasn’t realistic. What, I wondered, would have the most impact? Should I grow plants that perform other functions, like filtering the air? Should I look toward something like blue spirulina, which several readers of my first Medium piece on the project emailed me to suggest as a space-efficient superfood?

As you do a bit more gardening, you might also be surprised how similar gardeners are to coders and other technologists.

When the pandemic hit, that question rapidly answered itself. The absolute best use for a Covid-19 garden, I found, is to grow ingredients that enliven and add interest to other foods.

I can’t even begin to describe the mental health benefits — at the height of the pandemic lockdowns, when going to the grocery store literally felt like a life-and-death endeavor — of taking some boring, pandemic-friendly canned food or store-brand boiled pasta and topping it with fresh basil, crushed sprigs of thyme, and sliced cherry tomatoes, picked a few minutes earlier in our garage.

One of the hardest parts of weathering a lockdown is fatigue. Sticking with the same routine day in and day out for months — with limited trips outside your home — is mentally and emotionally draining. So is eating the same foods for months on end. In the early days, we ate whatever shelf-stable staples weren’t sold out at Target or bought strange brands of pasta or canned goods by the box for absurd prices on Amazon.

Gardening itself has been shown to reduce stress. But the little handfuls of fresh ingredients that we harvested each week from our AeroGardens served their own, extremely important function: They allowed us to add color, freshness, and variety to the bland, generic things we were otherwise eating. That, in turn, lent a bit of variety, excitement, and connection with the natural world to the drab, monotonous process of quarantine.

Having that little bit of freshness in our diet made the lockdowns a tiny bit easier to tolerate — and gave us one fewer reason to go to the store. When the world is falling apart outside your door, don’t underestimate the power of a handful of Thai basil or a drink topped with mint you grew yourself to make things just a bit better. It’s an effect that’s been around since the victory gardens of World War 1, and it’s something that thousands of us are rediscovering today.

Even if you’re more familiar with the silicon variety of random trees than the ones found in a real forest — or if your historical track record with plants isn’t stellar — now might be the perfect time to try out gardening. Gadgets like the AeroGarden make the process simple—and especially with more complex models that allow you to track and tweak light levels and feeding schedules, downright geeky.

As you do a bit more gardening, you might also be surprised how similar gardeners are to coders and other technologists. Take one look at an experienced gardener’s charts of hardiness zones and little grid-based garden maps drawn on graphing paper or mapped in Excel, and you might feel a sense of familiarity. If you want to take a stab at growing your own plants, you could do what I’ve done and make your garden extremely automated and tech-intensive. I’m still planning to work solar power from my private microgrid and a self-watering system into mine. My garden is, of course, more a platform for experimentation than an economical way to grow produce — accounting for the mining PC and Monnit sensor system, I estimate that it cost about $1,200 to build. But even if you just buy an AeroGarden and put in on your kitchen counter — or borrow a few of the ideas I’ve demonstrated and create your own DIY versions — that’s a great start.

I’m still reluctant to call myself a full gardener. That title goes to the people who effortlessly call up plants from the soil or, like my son, have a passion for the watering and pruning that managing a full garden often requires. But I’m comfortable calling myself a technologist who dabbles — or perhaps as Wired suggests, a “domestic terraformer.” And I’m proud to say that I now have the tomatoes to back up that title.

Co-Founder & CEO of Gado Images. I write, speak and consult about tech, privacy, AI and photography. tom@gadoimages.com

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