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What I Walked Into at a Near-100% Humidity Vertical Farm

Imamura here. While visiting a client’s vertical farm, there was one facility where the moment I stepped into the growing room, I could tell something was off.

The Moment I Stepped into the Growing Room

“Thank you for having me today.”

On the day I visited the client’s vertical farm, I straightened my suit jacket collar and gave my usual greeting. I’d been called in as a consultant for facility improvement.

But the moment I opened the door to the growing room, the air was heavy. Not hot exactly — more like something damp pressing itself against my face. When I breathed, I had the sensation of inhaling water vapor all the way into my lungs.

My glasses fogged up instantly. My field of vision was gone, and for some reason the floor was all I could think about. I took a step forward — and heard a small splashing sound beneath my leather shoe.

Splash. Splash.

I wiped my glasses and looked down. The floor was under about a centimeter of water. Between the grow beds, water was flowing like a small stream. I had a brief but genuine thought: maybe I’ve come to the wrong place in a suit.

“Um… and this water is…?”

“Oh, this? It’s just condensation from the walls collecting.”

The facility manager answered in a tone so light it might have been “would you like some coffee?” I, meanwhile, had already begun worrying quietly about the future of my shoes.

The 99% Humidity Room

The hygrometer read “99%.” Ninety-nine percent should be nearly the upper limit — but physically, it felt like it had exceeded even that. It wasn’t humidity so much as the sensation of standing inside a thin fog.

Water was streaming down the walls in rivulets. Drops were falling from the ceiling, one by one. The sound of the air conditioning — something I wouldn’t normally notice — seemed to come from far away, drowned out by the sound of falling water.

“The dehumidification equipment…?”

“There isn’t any.”

The moment I heard that answer, several items arranged themselves uninvited in my head. Condensation. Drainage. Disease. Legginess. Actually — dehumidification first. Inside, I was saying “this is a serious problem” in a rather loud voice.

The Mysterious Lettuce

While making my way around the growing shelves, I came across a strange plant.

“Is this… a new experimental variety?”

From a piece of polyurethane foam — the sponge-like material used as growing medium — a single slender stem was extending upward. At the top, a few small leaves. The shape resembled carrot tops a little, but it clearly wasn’t. It looked like a plant trying its best to grow upward in a place with too much water.

The facility manager answered with a slightly embarrassed look.

“Actually… this is lettuce.”

”…What?”

“It’s frilly lettuce — a variety with ruffled, wavy-edged leaves.”

I couldn’t believe what I was seeing. When I picture lettuce, I picture leaves spreading out in a loose, voluminous shape. But what was in front of me looked nothing like something you could sell. Even now as I write this, the image of those few small leaves at the top of that skinny stem comes back to me with strange clarity.

In that moment, the word “legginess” surfaced from a plant physiology lesson — the condition where internodes elongate abnormally under insufficient light — compounded here by the extreme humidity — causing the plant to grow far from its normal form.

Emergency Measures and What Followed

The situation was clear. This vertical farm’s humidity management was not keeping up.

There was no dehumidifier in the facility, but fortunately several air conditioning units had been installed. As an emergency measure, I proposed a rather brute-force approach: running both the cooling and heating modes simultaneously.

“At the same time? That’s going to run up the electricity costs…”

“That’s not the issue right now.”

I think I phrased it more diplomatically than that, but the feeling was accurate. Running cooling and heating together isn’t efficient if you’re only looking at electricity costs. But at that moment, the priority was simply removing moisture from the room.

A few hours later, the hygrometer reading started to come down slowly. 95%, then 90% — and by the next day the reading had dropped to the 80s. The hours before the numbers started moving felt unusually long. Check the hygrometer. Look at the floor. Check the hygrometer again. Whatever else you did, you always ended up back there.

Later, the facility formally introduced dehumidifiers and also set up a proper drainage system. When I revisited a month later, the elongated “lettuce” from before had grown into proper lettuce.

“So this is what lettuce actually looks like…”

The change was so dramatic I nearly said it out loud.

This experience gave me a concrete sense of just how important proper humidity management is in a vertical farm. Plants are resilient. Give them the right conditions and they respond. But at the same time, when the environment breaks down, they show it in their shape — more plainly and directly than you’d expect.

Even now, when I see the numbers on a hygrometer, I think of the splashing sound on that floor and the frilly lettuce with its slender stem. In a vertical farm, humidity isn’t just a matter of comfort. It’s a critical management variable that can change the shape of the crop itself.