Seasons of unseen growth

During autumn my body often begs for extra sleep. On those rare sunny mornings in November, the bright flood of light in my bedroom doesn't inspire me to leap out of bed, rather to lie sprawling in its precious, comforting warmth. The outdoors seems to slow and wane. Trees drop their brilliant leaves and flowers choke off their final display.

Fall may seem like a time of fading and senescence. By the time of snowfall, much of nature appears to have died or fallen asleep.

In reality this season of change is most crucial to long-term health and growth in the landscape. Autumn labour is vital to the garden. For many perennial plants, especially trees, this is the best time for planting and transplanting.

Conserving resources

Leaf drop or senescence may be the most obvious natural process at this time. Whole soy bean plants respond to shortened day length and decreased temperature by dying, shunting all available nutrients to the seeds which carry energy to the next generation of plants.^[2] Other plants respond more selectively, shutting down certain parts like their leaves, but not others. The physiological reactions that trigger senescence are little understood.

At the same time, perennial plants go through an invisible but essential period of accelerated root growth. The various parts of a plant compete for nutrients throughout the year. But after shoot and leaf growth cease in midsummer, more resources become available for the roots. Increasing autumn moisture fosters ideal conditions for the roots.^[3]

While leaf growth and death undergoes a vital cycle triggered by daylight and air temperature, root growth can be continuous as long as soil temperature is sufficient to support it. It practically stops when the soil drops below 13°C (55°F).

Growing in darkness

But in fall the soil remains relatively warm. This is an essential time for the tree's root system to penetrate new volumes of soil in search of water and nutrients. Sugars photosynthesized in the leaves retreat below ground, where they are necessary for cell growth and absorption of moisture and compounds from the soil.

For a thorough and engaging essay on the physiology of this process, read Roots: the unseen half of growth, by Mark Longstroth.

The impact can be observed in a poorly transplanted tree. This can occur if the soil is not prepared properly or the plant is moved during leaf growth, when it is more vulnerable to stress (for best results, move trees while they are dormant^[1]). It may sit

Go To Page: 1 2

Articles in this Topic    Discussions in this Topic