~ Jessica S. Herwick
I will admit, I have never been a huge fan of flowers, and I primarily plant them to bring the honeybees I scatter several pollinator friendly flowers throughout my garden areas every year. I prefer the most natural flower garden, to watch them emerge, bloom, and remain; letting their seeds drop to the ground in hopes of volunteers sprouting up next spring. But, today I had to do it. I picked one of my zinnias. I couldn’t help myself.
At first I noticed this particular flower while watering. From the front, it seemed like an ordinary cut-and-come-again. I passed it dozens of times. But as I reached behind the leaves, I discovered the severe curving and turning of its stem – and it was such a striking example of the phototropic reactions in my Zinnia bed I couldn’t resist. I was so delighted with the shape, I impulsively clipped it and brought it inside to photograph.
As I sprayed it down with water to wash the dust off the petals and leaves, my zinnia disclosed yet another surprise. The most unusual little bug emerged, scurrying back and forth along the curled stem like a miniature rollercoaster. It was very small, barely noticeable to the naked eye. I have never seen a bug like this before (and I stop to look at a lot of bugs). Since he was trapped in the loops of the zinnia stem, I had time to use a close-up lens and capture the image. See the close-up here. I have yet to identify this little guy, but I have a call into the Hort-Hotline!
My experience with the Zinnia bed this year has reminded me that sometimes gardening can be silly and fun. Sometimes it’s not about perfection, but the surprises that emerge when we stop trying to force our flowers to grow straight, leave them as they are, and allow the bugs to land.
So – What exactly happened to the stems of my Zinnias?
The curved stems were caused by the perfect storm of plant biology, my lazy gardening and some hard falling rain. I was too busy to stake the flowers earlier in the season, and then my gardening habits were interrupted by several days of heavy winds and thunderstorms. When the rains passed, I returned to my garden duties to find the Zinnias had tripled in size and become top-heavy - laying down from the weight. Buds were already forming, so I left things as they were, undisturbed for several weeks. Shortly after the blooms began, I was forced to lift the flowers up from ground level, after an unsuccessful battle with a community of snails. The results of staking the flowers so late resulted in some interesting twists and turns within the flowering stalks.
- The word tropism comes from the Greek ‘tropos’ which literally means, “a turning”. Scientifically, a tropism refers to the growth or turning movement of a biological organism in response to external stimuli. In the case of phototropism, the biological organism is the zinnia and the external stimulus is the light of the sun.
- A phototropic reaction occurs when the growth chemical auxin within the plant-part reacts in response to the plant-parts desire to be closer or further from the light. Auxin is responsible for reshaping the cell wall to help the plant move itself towards the light (as with the positive phototropism of the flowering stems of a plant reaching for the sun), or away from the light (as with the negative phototropism of the roots of a plant burrowing into the ground).
- Phototropism is the reason behind the lucky bamboo you may have seen twisted into various shapes such as a spiral or a heart. You can manipulate the growth of many plants by controlling the amount and direction of the light source. Of course, in my flowerbed the turned stems and twisted stalks were unintentional, but equally as fascinating.
Fun Facts About Zinnias
- Zinnias were originally cultivated by the Aztecs, and remain most diverse in their native lands of Mexico.
- They prefer well-drained soil and full sun, and have spread throughout the Southwestern United States to South America.
- These lovely and diverse flowers were not named until the 18th century, when botanist Carl Linnaeus of Sweden named the Zinnia to honor his German colleague, Botanist Johann Gottfried Zinn, who was the first botanist to study them scientifically.
To Learn More
Philadelphia Master Gardener Related Link – Annuals from Seed… Zinnia
PSU Cooperative Extension Selecting and Growing Zinnias for Cut Flowers
Penn State Cooperative Extension Fact Sheet on Plant Diseases Specific to Zinnia
North Carolina Cooperative Extension Fun Science Project (Kid Friendly)