Do Pennies Keep Cut Tulips from Drooping?

Last Updated (Tuesday, 08 March 2011 11:15) Written by Raymond Nakamura

Abstract

Nope.

Introduction

Once upon a time, I'd heard about putting pennies in the water of cut tulips to keep them from drooping longer. Various people I have asked also swear that it works. People generally associate copper with pennies and I imagined that copper could have had some effect on tulips. It is is an important micronutrient for plant growth and it's used to treat aquarium fish diseases. But I couldn't find any direct evidence of its usefulness on tulips, so I decided to see for myself, at least on a small scale.

Materials and Methods

Flowers

I bought two bundles of five tulips from a local grocery store. I don't really have a big budget for this blog. The petals were still closed. One bundle was purple and the other was red and yellow. I didn't consider their significant in flower language. Apparently these were grown somewhere in Canada. The flowers were out of water for about ten minutes during my walk home from the store.

Containers

I didn't have enough vases, so I used ten plastic beer cups (unused).

Water

The instructions on the wrapping said to use water at 20 C. I didn't have a thermometer so I felt it so that it was obviously hot or cold. I had to keep checking as I filled the cups up to the top ribbing about 3 cm below the lip. I did not refill the water during the course of the study.

Pennies

I tried to get new pennies, but my bank wouldn't give me any. The composition of pennies was different before 2001, so I limited myself to Canadian pennies from 2002 and later.

Set Up

I cut off 1-2 cm from the bottom of the stem at an angle. I put two pennies in two of the red and yellow tulips and three in the purple for no reason other than to have pennies in half of the total. And I didn't think I could assume the different bunches would be the same.

Then I placed them on my north-facing window ledge. To sort of randomize the order, as I was about the set them down I would check the seconds on my stop watch. If it was even, I put it down. If it was odd, I put it at the end of the line. So this mixed them up from the original order. This helped me not think about which ones had pennies in them. I didn't look into the cups and didn't write them down as a partial attempt to reduce my bias in measuring them.

I made a tic tac toe grid with masking tape across the mouth of each cup and placed the stalk in the centre square. I didn't do it too tightly because of the leaves. I placed the flowers so they all faced away from the window.

I taped an old battery to weight a string as a plumb line and measured to the base of the flower. So it is off by the diameter of the battery in all measurements. I didn't recalibrate for that. Then I measured the string on a ruler.

Results

They all seemed kind of bent to begin with. I was surprised to realize how they straightened up within an hour. Here's a graph showing the height of the tulips, averaged for those with pennies and those without. I was looking for some obvious differences and avoided any elaborate analyses. They look pretty much the same to me.

Here's how the flowers looked on the ninth day.

Discussion

So I couldn't find any difference between tulips with pennies and those without. I'm sharing these because negative results tend to be under represented in science. It might take longer for differences to show up, so I'll keep measuring them until all the petals fall off.

I was testing for the usefulness of pennies now. But once upon a time (before 1997), Canadian pennies were 97% copper. Today they are 4.5% copper plating. And they cost more to make than they're worth. If copper makes a difference, then older pennies may have shown a significant difference. If anyone has a stash of older pennies and repeats the tulip experiments, let me know what you find.