No matter what grade they’re in, there’s a better than good chance that many of your students are using drugs, specifically stimulants. It’s caffeine, man, caffeine. And the kids are into it these days, big time, and it’s killin’ ‘em. Hell, Kevin’s been to rehab like three times tryin’ to kick the stuff.
All that said, caffeine is wonderful and it’s my best friend and I wouldn’t want to live in a world without it. Knock out this little Demo Science science demo to show your students some of the beneficial properties of the ‘feine. Lots of gardeners—yours truly included—put used coffee beans in with their soil or compost to boost plant growth. But is it the caffeine that does the trick, or the increased nitrogen, potassium, and phosphorous coffee brings to the game?
Playing the Long Game
Unlike most of the experiments presented here, which can be completed in a single class period, this one takes a while. You’ll be growing plants, after all, and that can take a while. So ask your students to be patient as this one plays out over a few weeks.
For this experiment, you’ll need a packet of seed beans (I like to use mung beans, because “mung beans” is fun to say, but any kind will work; similarly, it could be any kind of seed, but beans grow pretty quickly and seem to yield the best results in this particular demonstration), three smallish garden pots, ample soil to fill said pots, water, caffeine tablets, powdered coffee (not ground beans, the crappy “coffee crystals” kind, like Sanka), a couple of beakers, measuring spoons, a digital scale, and a black permanent marker.
Fill your three pots with equal amounts of soil, plant ten beans in each pot. For the first five days, water all three pots with plain ol’ tap water and allow them to germinate. At the end of the fifth day, have your students measure the height of each plant and find the average height of the lot of them. (Obviously, have them write all this jazz down.)
Then, ready a caffeine-only solution by dissolving about 10 grams of caffeine tablets in 100 ml of water in one of your beakers. Be sure to label it “caffeine” to avoid future confusion. Fill your other beaker with roughly 100 ml of coffee, and label it “coffee”.
Determine which plant will receive which liquid, and label each pot with the appropriate label: “caffeine,” “coffee,” or “water.” (You could use a permanent marker, sure, but if you really want to blow your students’ minds–and add more science to this demo–get yourself a laser part marking machine and blast some high-tech, borderline sci-fi labels onto your flower pots.) Over the next 10 days, have your students water each plant once a day with the appropriate liquid. At the end of each day, have the kids re-measure and re-record the heights of each plant, as well as the daily average by pot. What do they observe as time goes on?
If everything went down like it should, your students will notice that the mung beans that were watered with coffee grew taller, faster than those watered with, um, water. They’ll also note that the plants watered with the caffeine solution grew more slowly than their counterparts.
Though it won’t get you published in Scientific American again anytime soon, this experiment does prove definitively that it’s not just the caffeine that makes plants grow faster. Instead, it is the potassium, phosphorous, and/or nitrogen in the coffee beans that causes the effects. As it does to fragile young minds like Kevin’s, straight up caffeine can cause growing plants to wither and turn brown.
For another take on this science demo, try growing a different plant, such as corn. Or, use something other than coffee, such as soda or richly-brewed tea.