This is the second installment in our summer break science project series. This time, let's skip the formal talk and focus on the simple "how-to-grow" experiment and its results. The topic is the ever-challenging "summer survival" for succulents (Honestly, I meant to publish this before summer, but I just couldn't write fast enough... sorry!).

Let me say this upfront: when it comes to helping succulents survive the summer, the basics are "keep them someplace cool with good airflow." That’s pretty much it. Of course, how much you water depends a lot on the type of plant and your environment. Sometimes you might need an industrial-sized fan for proper airflow, and honestly, there might not be such a thing as a "cool" spot outside in Japan. These factors make summer survival quite the challenge...

But this time, I want to share a universal summer survival technique that eliminates all those detailed factors like region, home setup, or personal sense—a method anyone can do, in any house.

Japanese summers are HOT!

People often imagine succulents as desert plants, so they’re surprised to hear that "succulents actually struggle with Japan's summer heat."

The main reason? Japan's summers are extremely humid. Succulents are adapted to dry climates—even deserts. In Japan's rainy, humid summers—where mold and bacteria thrive—they just don't have enough resistance to fend off those threats.

Another surprising fact: Japan's summers are often "hotter than deserts." Deserts aren’t deserts because they’re blazing hot, but because they’re dry. Many deserts aren’t as scorching as we might think. Also, most succulents hail from places like Mexico and South America—often at higher elevations—or South Africa, which is at a higher latitude (closer to the South Pole), so even in their hottest season, the temperature is pretty comfortable: 25–30°C. Even in Rio de Janeiro, which sits in the tropics, highs rarely top 30°C. With recent warming trends, Japan’s muggy heat is now said to rival the subtropics of Southeast Asia (who knows, maybe our landscape will start looking like a jungle soon).

Summer survival techniques for succulents

With all that in mind, most succulents just can't handle Japan's summer. Aeoniums and Echeverias will be wiped out. Haworthias are somewhat stronger, Agaves are even tougher, but none are invincible—you'll need some kind of strategy. In general, there are two big approaches.

Withhold water and induce dormancy

This is the go-to method for most people. The single most reliable approach: while your plant is still healthy in early summer, cut off the vigorous tips and place them in a bright, airy shade (see my earlier article for details). If you have only a few, just placing the potted plants in a bright indoor spot works, too. The key is to keep them out of direct sun but not in complete darkness; too much shade will make them leggy, even when dormant. Aim for just enough light to prevent stretching.

Keep up the watering and maintain plant health

The biggest drawback of dry dormancy: your plants will look scrawny. They'll shrivel, and as they use up the water in their lower leaves, those will dry out and die, making the healthy part much smaller. If you want your plants to stay plump through summer—and be ready for a healthy start in the fall—you’ll need to avoid total dryness. That means finding an even brighter, more ventilated spot where any water you give dries out quickly. But how frequently should you water? Well... it really depends on your environment. And that, honestly, is why people fail at summer survival (sweat). To be real: it’s pretty advanced stuff.

The one room every home has—always cool, veggies never spoil! What could it be?

If only there were a way to keep succulents healthy in summer that was simple and foolproof for everyone. The first thing that came to mind was using an air-conditioned room, but it turned out to be harder than I thought—plus, with electricity bills at ¥30,000–¥40,000 a month, it definitely isn't accessible for everyone. What if there was a tiny, super-insulated space that could keep cold air sealed in? Even a really small one, just big enough for plants...

Wait. We already have one: a refrigerator.

Can you use a refrigerator? Great for cuttings!

So, I ran a little experiment and put some succulents in the fridge. Check out last year’s article for details.

Kokirino-san also tried it and reported her results (Japanese).

The verdict: as a way to keep losses to a minimum using "induced dormancy," the fridge is excellent. A couple of notes—the veggie drawer might get a bit too cold, and some varieties could suffer from cold damage. And since it’s dark and you can’t water them, it’s not suitable for long-term storage (over 1–3 months).

The ultimate fridge method, perfected through trial and error

But wait—a true solution would keep plants healthy and plump for much longer. The two main hurdles: too dark and too cold. Could we tackle those with a little creativity?

LED lighting

When growing plants in darkness, LED grow lights are the thing to try. I squeezed one into the fridge, running the wire through the door gap (not the prettiest install, sorry!). I set up a timer outside the fridge to keep the light on about half the day.

Fridge timer control

Next problem: still too cold. Fridges often let you adjust the temperature, and with mine, I could set it as high as 12°C. But fridges are *too* good at keeping the temp steady—literally 12°C, never even wavering by a whole degree. But 12°C is still too chilly for plants, and in nature, temperatures don’t stay perfectly constant—the only place that happens is maybe Pluto!

Here’s where the LED bulb sparked an idea: connect the fridge itself to a timer. And since old-school timer outlets let you set intervals as short as 15 minutes, you can fine-tune how often the fridge cycles ON/OFF. With careful tweaking, you can simulate natural daily temperature shifts.

Here’s a graph I recorded after adjusting the settings: temps ranged from 16°C to 27°C. Pretty ideal for succulents!

The infinite-watering system

Last challenge: watering. It's tough to check and water plants hidden away in a fridge. But the fridge has a built-in water source—the cooling plate! When it's on, the plate frosts over; when it's off, the frost melts and drips down. If you can collect that, problem solved.

So I set up a deep tray beneath the pots and tilted the cooling plate so condensation would drip into it. For other containers, I trailed wicks to draw in water. This way, the setup was "always full," and I never had to water at all.

Since the fridge is sealed, condensation forms on the cooling plate → collects in trays → roots are watered → plants transpire → more condensation forms… a nearly 100% water cycle! If the humidity runs too high, maybe the plants are transpiring a lot, or maybe some moisture sneaks in from outside. You might want a desiccant to help, but getting the amount right could take some tinkering.

The result: even after over a year left alone

At first, I was so excited everything was working that I peeked in on the plants often. But life got busy, so weeks went by without checking at all. Before I knew it, it’d been over a year since I’d even opened the fridge. What happened to the plants left inside for a full year? Here are the results of leaving them in the fridge, completely unattended, for one whole year.

In summary

So there you have it—a "real-life test" backed by a year of patient trial. With easy control over light and temperature, this could very well be the ultimate environment for succulents. Wondering what kinds of plants, and what appearances, might result in such an ideal setting? I think it's a fascinating avenue for further experiments. Stay tuned for future updates!