Guest Blog: 200 Pounds of Earth

Bob Jenkins

Special thanks to guest blogger and  friend Bob Jenkins, gardener, writer, and story-teller extraordinaire who wrote the inquisitive 200 Pounds of Earth.

Jean Baptista van Helmont (1577-1644) conducted one of the classic experiments in plant growth. Van Helmont describes his experiment:

I took an earthen pot and in it placed 200 pounds of earth which had been dried out in an oven. This I moistened with rain water, and in it planted a shoot of willow which weighed five pounds. When five years had passed the tree which grew from it weighed 169 pounds and about three ounces. The earthen pot was wetted whenever it was necessary with rain or distilled water only. It was very large, and was sunk in the ground, and had a tin-plated iron lid with many holes punched in it, which covered the edge of the pot to keep air-borne dust from mixing with the earth. I did not keep track of the weight of the leaves which fell in each of the four autumns. Finally, I dried out the earth in the pot once more, and found the same 200 pounds, less about 2 ounces. Thus, 164 pounds of wood, bark, and roots had arisen from water alone.”

I first learned about van Helmont’s experiment from Michael Pollan’s collection of essays, Second Nature: A Gardener’s Education. Let’s pause for a moment while you link up to your favorite on-line book vendor and order Second Nature.

OK? Book on order? Let’s get back to the magic.

So, van Helmont grows a 169 pound tree and depletes the soil by only 2 ounces in five years. Suppose he had composted the tree’s fallen leaves, certainly more than 2 ounces, back into the soil. He would have ended up with a 169 pound tree and more soil than he started with!

Doesn’t this violate certain thermodynamic laws, not to mention a couple of pithy sayings, such as “you can’t get something for nothing” or “there’s no such thing as a free tree.” Where did all that mass, that weight, that substance come from? Even if you could remove all the water from the tree, you would still have more stuff than you started with.

This is one of the real “miracles” of gardening. Year after year, you literally take more out of the garden than you put into it.

I actually know where all that extra “stuff” comes from. Do you?

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4 thoughts on “Guest Blog: 200 Pounds of Earth

  1. Love the experiment! I only wish it had been mentioned in my plant biology course in college, then I would be able to answer Sheryl’s question, which has now become my question…..Where does all that extra “stuff” come from?


  2. Through photosynthesis, water and atmospheric molecules are recombined into solid mass (the 169 lb. tree). Of course, the tree also needs nutrients, but these arrive via the soil in very tiny amounts. How tiny? In the van Helmont experiement, minuscule, but in real applications, a farm, for instance, the “inputs” of nutrients can be quite significant depending on the soil you start with and the type of plant. If you’ve ever tried to grow corn, you know what I mean. You feed and feed and feed corn. There are several other variables, but photo-synthesis is the gist of it. Look at that word again: photo–synthesis.

    The more ethereal explanation might posit that the extra mass is made from sunlight.


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