Radiolab – "Smarty Plants"

Release Date: February 14, 2018
Hosts: Jad Abumrad, Robert Krulwich (WNYC Studios)
Main Guests: Dr. Monica Gagliano, Jennifer Frazer, Atish Bhatia, Sharon De La Cruz, Peter Landegren

Episode Overview

In "Smarty Plants," Radiolab investigates the intelligence of plants, exploring the surprising ways in which plants sense, respond, and even appear to "learn" from their environment. Through lively storytelling, hands-on experiments, and conversations with researchers, the episode challenges our animal-centric view of intelligence and perception, asking: Can plants hear? Can they remember? Can they be trained? And, ultimately, what does it even mean to be "smart"?

Key Discussion Points & Insights

1. The Plant and the Pipe: Following Water Underground

• [02:00 – 04:15]
  Hosts speak with Larry and Alvin Ubell, home inspectors, who observe that tree roots almost always grow toward buried water pipes—even if the pipes are sealed and not leaking—damaging infrastructure as they do so.
• Experiment by Dr. Monica Gagliano
  • She creates controlled pots where roots can only grow one of two directions: toward a buried (but sealed) water pipe, or away.
  • Result: 80% of roots grow toward the pipe, even though there should be no detectable moisture.
• Question: How do plant roots "know" where to grow if not by sensing water?
• Hypotheses debated:
  • Condensation from cold pipes ([06:08], Larry & Alvin)
  • Sensitive root hairs detecting minute gradients ([07:08])
  • Gagliano’s response: She eliminated moisture gradients by placing the pipe outside the soil ([07:36]); yet roots still grew toward the pipe.

“Wait, so… the pipe was on the outside of the pot? And the plant still went to the place where the pipe was—not even in the dirt?”
— Jad Abumrad, [07:52]

• Further hypothesis: Plants may sense the sound or vibration of water moving in pipes.
  • Gagliano tests this with recordings of running water ([08:15]), finding that most roots grow toward the sound alone.

“So they just went right for the MP3 fake water—not even the actual water, just the sound of it.”
— Jad, [09:11]

2. Do Plants Have Ears?

• [09:20 – 10:31]
  Jennifer Frazer (Science Blogger) considers whether root hairs at the tips of roots might make them functionally similar to our ear hairs, catching vibrations.

“Maybe plant roots are like little ears. … Maybe each root is like a little ear for the plant.”
— Jennifer Frazer, [10:18]

• Hosts ponder: Without a brain or nervous system, how could a plant "choose" which way to grow?
• Dr. Gagliano: Calls out the human obsession with brains as sites of intelligence, suggesting plants might have different systems for processing information ([10:41], [11:05]).

3. Experiment #2: Do Plants "Learn" Like Animals?

• [16:27]
  Focuses on the Mimosa pudica—a sensitive plant whose leaves fold up when touched, a reflex to deter herbivores.
• Gagliano’s Experiment: She drops potted mimosas from a short height onto foam repeatedly.
  • Initially, plants fold up leaves with each drop; after some repetitions, they stop, as if realizing the drop isn't a threat ([19:33]).
  • To control for fatigue, she shakes the plant side-to-side—immediately, the leaves close again ([20:04]).
• Interpretation: The plants have “learned” dropping isn’t dangerous—and remember that for days.
• Replication attempt: Princeton group tries to recreate the experiment but cannot reproduce the result, likely due to inconsistent treatment ([21:36]).
• Gagliano’s Data: Her plants remembered the drop for at least 28 days ([23:16], [24:08]).

“It was almost like… let’s see how much I have to stretch her here before you forget. … Eventually she came back after 28 days. And they still remembered.”
— Monica Gagliano, [23:52]

4. Pavlov’s Plants: Classical Conditioning in Pea Plants

• [25:47 – 31:20]
• Inspiration: Pavlov’s experiment with dogs salivating at the sound of a bell.
• Gagliano’s Experiment:
  • Trains pea plants by pairing a fan and a light from the same direction; plant always grows toward fan+light.
  • After conditioning, she turns on the fan alone from a new direction—plants grow toward the fan, anticipating food (light), like Pavlov’s dogs ([30:08]).

“These little… plants, my little peas, had indeed turned and moved toward the fan, stretching up their little leaves as if they were sure that at any moment now light would arrive.”
— Monica Gagliano, [30:26]

5. What Counts as “Intelligence”? The Debate

• [32:22 – 35:08]
  Lincoln Taiz, UC Santa Cruz, voices skepticism—not of the experiments per se, but of the language (metaphors of “hearing,” “learning,” “behavior,” etc.), warning against over-interpretation.
• Value of Metaphor: Producer Annie McEwen suggests that using animal-like metaphors helps open creative possibilities for experiments ([33:17]).

“Maybe it makes her sort of more open-minded than someone who’s just looking at a notebook.”
— Annie McEwen, [33:40]

• Ethical/Philosophical Implications:
  Larry Ubell comments that maybe intelligence is not unique to humans; perhaps we’re not smart enough yet to understand plants' intelligence ([35:08]).

“So they may have this intelligence. Maybe we’re just not smart enough yet to figure it out.”
— Larry Ubell, [35:34]

Notable Quotes & Memorable Moments

• On Plant Perception:

  “If a nosy deer happens to bump into it, the mimosa plant folds its leaves, curls all its leaves up against its stem.”
  — Robert Krulwich, [17:02]

• On the Implicit Threat to Human Exceptionalism:

  “Does it change my place in the world? Does it threaten my sense of myself or my place as a human that a plant can do this? No.”
  — Jennifer Frazer, [37:11]

• On Human Hubris:

  “You think this is a hubris corrector?”
  — Robert, [37:31]
  “Yeah.”
  — Larry Ubell, [37:35]

Timestamps for Key Segments

| Segment | Time | |----------------------------------------|--------------| | Introduction / Set-Up | 01:18–04:15 | | Root Sensing & Water Pipe Mystery | 04:15–09:50 | | Can Plants Hear? | 09:20–10:31 | | Brains vs. Distributed Intelligence| 10:31–11:36 | | Mimosa ‘Learning’ Experiment | 16:26–24:08 | | Pavlov’s Plants Conditioning | 25:47–31:20 | | Scientific Skepticism & Metaphor | 32:22–35:08 | | Big Picture & Philosophy | 35:08–38:02 |

Episode Tone

• Curious and wonder-filled, with the hosts bringing both skepticism and playful awe to the table.
• Conversational and experimental, as they attempt to reproduce the science themselves.
• Reflective, openly questioning human biases and the boundaries of scientific language.

Conclusion

"Smarty Plants" turns conventional notions of intelligence upside down, offering compelling evidence that plants can perceive, “learn,” and even be trained. Through interviews and experiments, the episode blurs the line between plant and animal abilities—raising deep philosophical questions about consciousness, memory, and the hidden life in our gardens and forests.

Takeaway:
Plants might not have brains, but evidence is mounting that they're much “smarter” than we think. Perhaps, as the hosts discover, this isn’t a threat—but an invitation to humility and wonder.