Why Do Plants Lose Their Green Colour in the Fall?
As fall rolls in, we say goodbye to the lush, green summer foliage and welcome the fiery reds, vibrant oranges, and golden yellows of autumn. But why do plants go through this dramatic wardrobe change? It’s not just about putting on a seasonal show for leaf-peepers. The transformation from green to colourful, and eventually to bare branches, is a survival strategy. Let’s dive into the science behind this leafy magic (spoiler: it's all about plant hormones and sunshine), and discover why your plants are ditching their green for fall.
The Green Days of Summer: Chlorophyll’s Reign
In the height of summer, plants are green because of a superstar pigment called chlorophyll. This pigment is key to photosynthesis, the process that lets plants convert sunlight into energy. As long as there’s plenty of sunlight, plants crank out chlorophyll like it’s going out of style, giving leaves that vibrant green hue.
But as the days get shorter and the sunlight becomes less intense, the plant doesn't need to work so hard at photosynthesis anymore. Less sunlight means chlorophyll production slows down, and eventually, the plant stops producing it altogether. When that happens, the green fades, and the other pigments hiding behind the chlorophyll start to steal the show.
Fall’s Fashion Show: Carotenoids and Anthocyanins
Once chlorophyll steps aside, carotenoids and anthocyanins come to the party. These pigments are always present in leaves but are usually overshadowed by chlorophyll’s green dominance. In fall, carotenoids give leaves their yellow and orange colours (think of carrots and pumpkins—same pigment). Meanwhile, anthocyanins provide the stunning reds and purples.
But not every tree or plant follows the same colour script. While some turn a brilliant yellow or orange, others, like maples, can go bright red or deep purple, thanks to higher levels of anthocyanins.
Why Plants Bother with the Colour Change
You might wonder why plants go through this whole fall colour spectacle in the first place. It’s not just to create a pretty backdrop for your cozy sweater photos. For plants, it’s about energy conservation and preparation for winter.
During spring and summer, leaves are working overtime to make food for the plant through photosynthesis. But in fall, when light is limited, it becomes inefficient to keep those leaves alive. So, plants pull back. The nutrients and energy stored in the leaves are sucked back into the branches, trunk, and roots to be stored for winter. This process is called senescence. Once the chlorophyll is broken down and the plant has taken what it needs from the leaves, it lets them go.
Why Do Some Trees Change Colour Before Fall
You might have noticed a few trees in your neighbourhood or garden starting to turn colour well before the calendar says it's officially fall. While most trees put on their colourful display in late September or October, some trees jump the gun and start the show early. Reasons behind this early transformation and what it might signal about a tree’s health and environment could be:
- Species Characteristics
- Environmental Stress
- Pests and Diseases
- Genetics and Individual Tree Variability
- Microclimates
Leaf Drop: A Strategy for Survival
Losing leaves may look like plants are having a rough time, but it’s actually a smart survival move. By shedding leaves, deciduous trees and shrubs reduce the risk of water loss during winter when the ground is frozen and water is hard to come by. Plus, leaves are a liability in a snowstorm—those flat surfaces would just catch snow, causing branches to snap under the weight.
Why Some Plants Stay Green
You’ve probably noticed that not all plants lose their green in the fall. Evergreens, like pines, cedars, and spruces, keep their green needles or leaves year-round. These plants have adapted to different strategies for dealing with winter. Their needles are covered with a thick, waxy coating that helps retain water, and their shape helps them shed snow more easily.
Bonus Fall Show: Why Some Leaves Don’t Change at All
Sometimes, you’ll have plants that don’t seem to get the memo about fall. There are a few reasons for this:
- Evergreens: As mentioned, they just don’t care about the seasons.
- Weather conditions: A sudden frost, excessive rain, or even drought conditions can alter or prevent the colour change.
- Species variations: Some plant species just don't put on a big fall display because they don't have high levels of those colourful pigments.
How to Embrace the Fall Transition in Your Garden
Fall colour can be one of the most beautiful aspects of gardening, so lean into it! Here’s how to make the most of the seasonal changes in your garden:
- Plant for fall colour: Add trees and shrubs like maples, oaks, sumac, or burning bush to your landscape for a burst of red, orange, and yellow when summer fades.
- Keep your evergreens lush: For contrast and winter interest, make sure your evergreens are healthy heading into fall. Give them a deep watering before the first frost and mulch their roots.
- Use fallen leaves: Don’t just rake up leaves and throw them away! Use them as mulch or add them to your compost pile to return nutrients to your garden soil.
- Appreciate the dormancy: Fall isn’t a time of death for your plants—it’s a time of rest. Your plants are storing up energy and preparing for next year’s growth. It’s part of the natural cycle that allows your garden to come back stronger in spring.
So, there you have it, the next time you look out at your garden and see the green slipping away, don’t worry—your plants are simply packing up for winter. They’re storing their energy, putting on one last colourful hurrah, and preparing for another round of lush growth when spring rolls back around.
And hey, now you can impress your friends with the science behind those beautiful fall colours (maybe over a pumpkin spice latte).
Happy gardening!