Autumn's soil is perfect for planting
Updated: Dec 14, 2020
Shortening days, cooler weather and the prospect of the first frosts of the season on the horizon: one might be forgiven for thinking the gardening calendar is gearing up for hibernation. True, the gardeners’ duties become less frenetic, but this season punches above its weight when it comes to planting trees and shrubs.
Critically, plants establish quicker into new ground during autumn and have a greater survivorship than those planted in any other season. The centuries old saying sums up the importance of planting at this time of year:
‘Plant a tree in spring and beg it to grow but plant a tree in autumn and command it to grow’
So why is autumn such a good period for planting trees and shrubs? The reason is the soil is warm from the summer and often moistened by recent rains. Conditions that tempt previously confined roots into new soil. With the naked eye it would difficult to see the proliferation of fine root hairs into the earth. Once on their journey of exploration of food and water the roots encounter and attach to naturally occurring fungi, called mycorrhiza (derived from the Greek for fungus and root), the threads of which are so small that 1000 would be needed to be placed side-by-side to measure a single millimetre. These cryptic fungi largely go unnoticed until some produce mushrooms we encounter in the garden and countryside..
Mycorrhiza association occurs on the roots of around 85% of all known plant species. This interaction can be traced back 450 million years to the period when the earliest land plants
made the transition from an aquatic to a terrestrial environment. The plant-fungus association is mutually beneficial whereby the fungus receives sugars manufactured by the plant and the plant obtains nutrients such as phosphorus and nitrogen along with water. The real benefit for the plant is that these microscopic fungi greatly increase the surface area where the plant can forage. So great is the combined mass of mycorrhiza, Natural England have suggested they capture a significant amount of soil carbon. The association can also increase disease resistance and change the chemistry of the plant allowing them to evade insect predators that use chemical signals to locate plants. In truth, scientists are still realising the importance of this plant-fungus association. But the main factor for the gardener is that the roots of autumn planted plants will explore the surrounding earth affording greater opportunity to intercept mycorrhiza, moisture and nutrients. Potentially making the difference between life and death for your cherished plant.
Mycorrhiza inoculum can be purchased in garden centres as a planting ameliorant. My advice, however, is that the abundance of naturally occurring mycorrhiza in most soils means additional inoculum is unnecessary. However, if you are planting on an impoverished soil or in the garden around a new build, additional inoculum would be beneficial.