Van Helmont’s Intriguing Experiment-

Excerpt from Bonsai Heresy’s Chapter 22 ‘More fertilizer, more better’

The seventeenth-century Flemish scientist Jan Baptist van Helmont did something remarkable. He proved that it wasn’t soil that built plant tissue.

Van Helmont designed a simple experiment. He took a large container, filled it with two hundred pounds of dry
soil, and planted a five-pound willow in it. For five years he gave it nothing but rain water or distilled water. At the end of five years he removed the soil, dried it, weighed it, and found that the soil was only 2 ounces lighter, weighing in at 199 pounds, 14 ounces. The willow weighed 169 pounds.

He concluded that “164 pounds of wood, bark, and roots arose out of water only.”

It was a brilliant experiment proving that plant tissue is not the result of transmogrifying great chunks of soil into cells. And he was mostly right, water does account for much of a plant’s structure. We now know it is all the ephemerals that build plant tissue: air, scarce minerals, and water. And mineral availability is increased by adding fertilizer. 


It’s a great, thought-provoking experiment. The success of van Helmont’s willow with no input of fertilizer is a tale we should tuck in the back of our minds—not to replicate it, as most bonsai can use some fertilizer, and some a LOT—but that each tree will have a need different than the next one on the bench. 

How we apply fertilizer to bonsai takes up the rest of the chapter. Several chapters, actually. One of the main themes is that broadcasting the same level of fertilizer on everything brings below average results. For we’re not just growing willows. (And few of us grow willows at all.) 

Bonsai Heresy is found at Stone Lantern

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  1. Super interesting. A related question is, put willow in bonsai pot with 5% of pot contents being root, 95% being bonsai soil. Repot 5 years later to find that willow is pot-bound—all roots. Where did the soil go?

    • crataegus says:

      The mystery of the disappearing soil…yes, that’s a good one. I think for the most part roots pushing the soil mass up from the bottom results in erosion of soil from the top. Washed off by watering. Then there’s nothing left but roots. Maybe.
      The experiment is a mind-bender. If you read it wrong you could be led to overwater trees. The other mistake would be to see fertilizer as the gas pedal—-since water and air are abundant—-and dump piles on. That’s the line I address in the chapter.

    • Maciek says:

      In addition to what Michael said in his reply, there is also the case of leaf litter, deadwood, and other organic matter in the topsoil and on the topsoil. Decomposers break these things down and respire CO2 into the atmosphere. So there is a pathway for carbon mass to leave the pot straight into the air, if any of the soil in the willow pot is organic that is.

      Humans aren’t too different: When you lose fat, the vast majority of it (84%) is exhaled via your lungs, so you’re removing a lot of organic material straight into the air. Meanwhile, poop is something like 60% dead gut bacteria by mass 🙂

  2. Martin Klein says:

    Nick Lenz used to say “You’re not trying to grow watermelons here.”

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