Japanese College Students Built a Sensor That Lets Your Bonsai ‘Talk,’ and Venture Judges Valued It at $171,000

Anyone who has killed a houseplant knows the problem. The plant cannot tell you it is thirsty until it is already wilting. A team of seven college students in Japan decided to fix that for one of the most demanding plants a home grower can keep, and they ended up building a device that lets a bonsai answer back.

The device is called Kotonoha, written ことの葉 in Japanese, a name that plays on a word for language and the word for leaf. It was built by a student team called mAIzuru at the National Institute of Technology, Maizuru College, a technical college in Kyoto Prefecture. The Asahi Shimbun reported on the project in Japanese on Oct. 5 and published an English version on Oct. 21.

According to the Asahi, the team is made up of seven fourth-year students from the college’s Department of Electrical and Computer Engineering and Department of Control Engineering. The college’s own announcement lists all seven members and says they belong to its Programmers’ Community club.

A sensor in the pot, a conversation on the phone

The hardware is simple. A needle-shaped sensor goes into the bonsai’s pot and collects data on soil moisture and fertilizer concentration, the Asahi reported. The team’s page on the contest website adds sunlight to the list of conditions the system tracks. The readings go to the owner’s smartphone, where an AI analyzes them and delivers the results as short lines of dialogue, written as if the tree itself were speaking.

The app also takes in information about the tree’s history from previous owners. That lets a grower ask questions the soil sensor could never answer on its own. In the Asahi’s examples, a grower asks, “How many years have you been around?” or “What kind of people have raised you?” Kotonoha answers with lines such as, “I think it’s been around 50 years. I had someone who would kindly water me in the morning,” or, “My roots are starting to dry a little.”

That second line is the practical heart of the product. Bonsai live in small, shallow pots that hold very little soil, so they can dry out quickly, and the timing of water and fertilizer matters a great deal. The personality is a friendly layer on top of a moisture and nutrient reading that tells the owner when to act.

It is worth being clear about what the conversation is. The tree is not remembering anything. Its “memories” come from the history that owners enter, and its comments on its own condition come from the sensor. The team says the more a grower talks with Kotonoha, the more data the device collects.

Where the idea came from

The project started with a frustration at home. One of the students had trouble keeping plants alive and wished, as the Asahi put it, that plants could tell people when they were in distress and how much water and fertilizer they needed in each season. The team’s page on the contest site frames the problem the same way: many people want the comfort of houseplants but end up letting them die.

The students chose bonsai in particular because of how long the trees can last. Some bonsai can live for more than 1,000 years, the Asahi reported, and the team was drawn to the idea of a plant passing from one generation of growers to the next. In that light, a record of who cared for the tree, and how, becomes part of the tree’s story.

“Bonsai’s personality can change greatly depending on its grower, the environment and climate,” team leader Toma Kai, 18, told the Asahi. He said Kotonoha “deepens the act of cherishing bonsai, which is a living art,” and supports the passing of that culture to the next generation.

Judged by venture capitalists

The team entered Kotonoha in DCON2026, the seventh National Institute of Technology Deep Learning Contest. The contest asks students at Japan’s technical colleges, known as kosen, to build products that combine hands-on engineering with deep learning. Teams are judged not only on their technology but on their business potential, with venture capital judges assigning each one a company valuation.

This year’s contest drew a record 119 entries, according to Maizuru College. Ten teams made the finals, held May 8 and 9 at Shibuya Hikarie in Tokyo. The college said it was Maizuru’s third year entering the contest and the first time one of its teams had reached the finals.

Kotonoha received a valuation of 27 million yen, which the Asahi put at about $171,000, and finished sixth. It also won the Minister of Agriculture, Forestry and Fisheries Award, along with corporate prizes from AccessNet, Pola Medical, SoftBank and Midas Capital, according to the contest’s published results. The college said the agriculture award recognized the project’s work to share bonsai, a part of Japanese culture, with the world and carry it forward in a new form. The top prize went to a sewer pipe inspection robot from a team at Toyota College.

The contest’s own report on the finals described Kotonoha as one of the moments that made the hall come alive. When a venture capital judge asked what a paying customer would get by spending more, the team leader answered that the bonsai could help plan that night’s dinner or even offer life advice, and the audience burst out laughing. The report noted that the project began from the students’ own love of bonsai rather than from a social problem, and that the team had gathered comments from bonsai enthusiasts overseas. Their mentor, Satoshi Sato, president of connectome.design, called it a lovely product that came from chasing what they love, according to the report, which is in Japanese.

What comes next

The students are already working on the next version. The Asahi reported that they plan to use AI to judge a bonsai’s health from photos of its leaves, estimate how its condition will change, decide on appropriate care, and build that advice into the conversations.

The team also hopes to turn Kotonoha into a business and is looking at markets outside Japan. “There are many bonsai enthusiasts even outside Japan,” Kai told the Asahi. “With Kotonoha, they can grow bonsai even if they are inexperienced. I hope they enjoy talking with bonsai.”

None of the reports we reviewed mention a price or a release date, or say when the device might be available outside Japan.

A lesson for any potted plant

Gardeners do not need a talking tree to borrow the idea behind Kotonoha. The core of the device is a soil sensor checked regularly and acted on, and simple moisture meters are already sold at garden centers. In the low desert, where containers on a patio can dry out in a single hot afternoon, checking the soil before watering, rather than watering by the calendar, is one of the most useful habits a container gardener can build.

What the Maizuru students added is a reason to check. A reading on a meter is easy to ignore. A message from a tree saying its roots are starting to dry is harder to set aside. For a plant that may outlive its first owner by centuries, that small nudge, and the record of care it leaves behind, could be the most valuable part of the design.