Leaf mould is ‘important for the garden’ and now’s the ‘perfect time’

Composts come in all sizes, materials and mixes, from peat-free compost to loam-based compost, seed compost to potting compost, but not everyone knows about leaf mould.

The name might sound a little odd, with some gardeners asking, “why is mould good for my garden?”, but the long, cold process of decomposing deciduous leaves into a wonderful crumbly mix full of nutrients and life has been a gardener’s secret for many years.

Leaf mould improves garden soils and can be used around the garden for multiple uses. The fungal breakdown of leaves, as opposed to fast bacterial degradation due to heat, as in the case for garden composting, results in micronutrients and microorganisms, or in other words a terrific organic medium bursting with natural organic activity. And, because there is no degradation, all organic extracts are undamaged.

Tree leaves contain foliar micro fungi living on (epiphytes) and inside (endophytes) leaf tissues. The fungal communities that colonize leaf litter produce a wide range of extracellular enzymes that facilitate breakdown. Lignin, cellulose and other compounds are broken down and turned into humus-rich leaf mold by the fungi enzymes.

As it continues to decompose it recycles vital components back to the environment.

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In natural settings of woodlands and forests, the fallen leaves accumulate on the ground as a natural layer and are referred to as leaf litter. It is the largest source of organic material and nutrients for the humus layer.

It also acts as a protective layer for the soil, preventing microhabitat fluctuations, soil erosion and compaction. A variety of organisms and wildlife, such as worms, mites, spiders and other invertebrates, use this leaf litter for shelter.

This in turn provides nesting material and food for birds. Therefore, it is so important for the garden setting.

The process of making lead mould could not be any simpler. The two main processes are a leaf bay/cage or black bin bags.

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As it is a cold process October is the perfect time to start collecting fallen deciduous leaves. Oak, hornbeam and beech make the best leaf mould, and each will create slight variations in texture.

Mixing them will therefore create a great combination. Tree leaves are rich in carbon, nitrogen, potassium, magnesium, sulphur, phosphorous and trace minerals.

Because leaves are high in carbon and low in nitrogen, typically with a carbon to nitrogen ratio of 60:1, they would need nitrogen-rich materials added to help with decomposition. Adding fallen leaves to high-nitrogen, standard composting bays will therefore aid faster decomposition.

Just like composting bays, leaf cages should have open sides to allow air to flow through the medium. Choose an area of the garden that can be easily accessed, but out of the way, unless you like seeing composting bays.

It needs to be shaded from scorching sun during the summer but not too sheltered, as rain should be used to dampen the leaf pile.

Rake up the fallen leaves and pile them in the bay/cage. Do not press them down as air pockets will speed up the cold process decomposition, known as aerobic decomposition. Also, moisture will help towards fungal growth and breakdown, which again will help speed up the decaying process.

The second method can be conducted in any size garden, even on smaller terraces and balconies. Take a couple of black bin bags. Rake up and pile the fallen leaves and when finished raking, place all the leaves into the black bin bags.

If the leaves are dry add a watering can of collected rainwater (tap water will do). Tie up the black bags and then with a garden fork, a small knife or pair of scissors make some drainage holes in the bottom of the bags.

In addition, well-rotted leaf mould (two years or more) can be used for sowing seeds. Alternatively, mix horticultural sand, leaf mould and garden compost in equal amounts as a general potting compost.

When added to planting holes, especially bare root hedging, trees and herbaceous perennials, leaf mould helps increase mycorrhizal fungi.

It forms a secondary root system for a plant, which has been shown to increase water and nutrient uptake by taking sugars from plants in exchange for moisture and nutrients.

The addition of leaf mould to your garden will help improve the wildlife from the smallest micro-organisms to large birds and mammals, help increase biodiversity, is better for the environment and helps towards organic gardening practices and sustainability. There is no waste and decomposed material will improve plant health.