Garden fascination: How climbing peas climb

Garden fascination: How climbing peas climb

Did you know??!!!

Climbing peas are an excellent use of space and are productive over longer periods of time than bush peas. This long season of harvesting makes them an excellent choice for home gardeners, who typically don’t need a bumper crop all at once but want a more sustained fresh harvest over weeks.

Climbing peas are amazing at using vertical space to capture tons of light energy. While many varieties grow a reasonable 4-6’, some reach 12’ plus in height. And they do this without the energy and time intensive process of growing sturdy woody trunks.  This vertical growth is possible because of tendrils, tiny appendages extending from the growing vines out into space hoping to contact something to climb. When those tendrils do contact something, such as the wrung of a trellis or fence, the tendrils begin to curve around it- eventually forming a nearly unbreakable attachment.

How do pea tendrils, which are botanically considered just modified leaves, grow this way?  Climbing plants and tendrils have fascinated botanists, scientists, and gardeners for centuries.  The earliest study that we know of of pea tendrils is Charles Darwin's monograph On the Movement and Habits of Climbing Plants.  In this work he coined the term circumnutation, which is the process by which the stems and tendrils of climbing plants seek structures to climb.  

Imagine your finger is a pea tendril and that it has been blowing in the wind and also moving through chemically activated circumnutation.  Its hoping to come in contact with something to climb. Suddenly, the pad of your finger contacts the wrung of the trellis. Amazingly, tendrils, just like human fingers, have the ability to sense through touch.  And, super amazingly, the pea tendril avoids wrapping around itself by sensing through chemoreceptors when it is contacting itself.  When your peas are growing this year, go out and see if any pea tendrils are wrapped onto their mother plant or each other!   

Next, a chemical signal is then sent to inform the cells that they are contacting something to grab a hold of.  If we continue with the finger-as-pea-tendril example, the cells on the other side of your finger will begin to elongate. This process by which plants grow in a certain direction via chemical signal is more generally called chemotropism.  As those cells elongate, your finger (the tendril) curves to accommodate the elongating cells. This curving continues until your finger has wrapped around the trellis 3 or 4 times.

But!  The tendril does not simply curve in one direction.  If it did, the tendril would twist the whole plant with it, making a topsy-turvy mess instead of a neatly climbing, light-maximizing vine.  Instead, using a process that was only understood recently, the two halves of the tendril curl in opposite directions.  So if you stretched a coiled tendril out and cut it in half length-wise, one side would be coiled one way, and the other the opposite way.  Inside the intact tendril, these two sides are separated by an uncoiled stretch, called a perversion, and the result is no net twist. This discovery has amazed scientists, and studying the cellular structure of the pea tendril has led to the development of a new kind of spring.  

It's just a fascinating, living world!

Fascinated enough to give them a grow? Check out our full line of pole peas here.