Last week I visited Batsford Arboretum, home to a unique collection of some of the world’s most beautiful and rare trees, shrubs and bamboos, spread across 60 acres.
The Arboretum is nestled in the Cotswolds Hills and was bursting with a splash of Autumn colour. There was plenty to see and some lovely woodland trails to walk amongst a fine collection of mature and newly planted trees.
It is at this time of the year, mid to late October, that we start to see the seasonal change in deciduous trees' behaviour. Essentially, the leaves changing colour and falling to the ground.

The main reasons why leaves fall in autumn are tied to changes in temperature, daylight, and the tree's preparation for winter survival.
As autumn approaches, the days get shorter, and temperatures begin to drop. Trees sense these environmental changes, triggering the process of shedding leaves. This is because leaves play a critical role in photosynthesis, where they use sunlight to produce energy for the tree. With less sunlight in autumn and winter, photosynthesis slows down, making it inefficient for the tree to maintain its leaves.

At the base of each leaf stem, there’s a specialised layer of cells known as the abscission layer. In autumn, trees start producing a hormone called abscisic acid, which triggers the formation of this layer. The abscission layer gradually cuts off the flow of nutrients and water between the leaf and the rest of the tree. As the abscission layer thickens, it weakens the attachment of the leaf to the branch, eventually causing the leaf to fall.

Shedding leaves helps trees conserve water and energy during the harsh winter months. Leaves are prone to drying out, and since water is scarce in winter (due to freezing), trees would lose a lot of water through evaporation from their leaves. Dropping the leaves allows trees to conserve both water and energy during the cold season, when growth halts.
As the tree cuts off nutrient flow to the leaves, chlorophyll - the green pigment responsible for photosynthesis - breaks down, revealing other pigments like carotenoids (yellow and orange) and anthocyanins (red and purple). This is why leaves change colour before falling.

Different species produce varying levels of pigments, resulting in different colour ranges. For instance, maples often turn bright red, oaks may turn brown, and birches often turn yellow.
Warm, sunny days followed by cool nights enhance anthocyanin production, resulting in more vibrant reds and purples. Cloudy, rainy weather tends to reduce the intensity of colours.

Soil pH and nutrient levels can also affect pigment production. For example, more acidic soils can deepen red hues in certain species.
In essence, the beautiful array of autumn leaf colours is a result of the breakdown of chlorophyll and the visibility of other pigments like carotenoids, anthocyanins, and tannins, influenced by environmental and species-specific factors.
Leaves create a large surface area that could catch snow and heavy winds, increasing the risk of damage to the branches. By shedding their leaves, trees reduce this surface area, minimizing the risk of limbs snapping under the weight of snow or the force of strong winds.

In summary, leaves fall in autumn due to the tree's response to reduced sunlight and cooler temperatures, the development of the abscission layer, and the tree’s need to conserve energy and water, and protect itself from winter damage.
Why clear fallen leaves?
It has always been the norm for turf professionals to clear leaves from natural grass amenity and playing surfaces for several important reasons:
To maintain grass health:-Leaves can block sunlight from reaching the grass, which is crucial for photosynthesis. Without sufficient sunlight, the grass can become weak, lose its colour, and potentially die.
Trapped moisture:- A thick layer of leaves can trap moisture, creating an environment that encourages fungal growth and disease. This can harm the grass and lead to unsightly patches.
Drainage issues:- A buildup of leaves can block drainage systems, especially in areas with heavy rainfall, leading to waterlogged conditions. Poor drainage on playing surfaces can make them unusable and potentially hazardous due to slippery conditions.
Playability and safety:- For playing surfaces like sports fields (e.g., football, rugby, or cricket), accumulated leaves can make the surface uneven, slippery, and difficult to see. This increases the risk of injuries to players.
Leaves can obscure the lines and markings on the field, making it difficult for players and officials to see boundaries, goals, or other important markings.
Aesthetic and usability:- From an aesthetic standpoint, a surface covered in leaves can look untidy, making it less inviting for public use.
For amenities like parks, picnic areas, and walking paths, leaves can create slippery surfaces and become a tripping hazard.
Prevention of thatch build-up:-Leaves that aren't removed will eventually break down and contribute to thatch, a dense layer of organic matter that can choke the grass and reduce the penetration of water, nutrients, and air into the soil.
Pest control:- Decaying leaves can attract pests, including insects and rodents, which may further damage the grass and surrounding areas.

To maintain healthy, safe, and usable grass surfaces, regular clearing of leaves is necessary, particularly during the winter months October through to January when leaf drop is heaviest.

Gone are the days when we spent hours manually raking leaves. We now have a plethora of leaf blowers on the market that are both pedestrian and machinery driven, such as large leaf blowers attached to gators and tractors. We also have large mechanical vehicles that are solely designed to pick up leaves by means of brushes and vacuums.
We are also into the realms of battery powered blowers that have become popular over petrol driven one in recent years. All these leaf blowers, brushes and vacuums have certainly made the job of clearing up leaves so much more efficient and cleaner.