Improving the soil with leaf-mould

 

Anyone who lives in this part of Great Britain knows the problems created by leaves at this time of the year. Yet they can be of great value if used wisely at the farm or in your garden or allotment.

Why is leaf-mould useful?

 It’s not that leaves have great nutritional value. The tree tends to suck the nutrients out of the leaves before they drop them. Well-rotted leaf-mould greatest benefit is as a soil conditioner, improving the structure of a soil, rather like peat, but without the damaging environmental costs of extracting peat. Leaves tend to have a high Carbon:Nitrogen ratio, averaging around 50:1 and low levels of essential nutrients: Nitrogen 0.66-1.62%, Phosphorus 0.02-0.29%, Potassium 0.09-0.88%.

Leaves also contain useful amounts of Calcium and Magnesium.

How do you make leaf-mould?

First brush up your leaves or rake them off a lawn. We actually collect several wheel-barrow loads from our road. Then there are several options for making use of it;

1.     Store leaves in bin liners. Moisten the leaves if they are dry and prick holes in the bag. Tie loosely, pile up the bags and leave in a quiet spot for up to two years.

2.     Build a chicken wire frame in a hidden corner of the garden about 1m³ and pile up with leaves. Turn the pile occasionally. (See the frames at HCF).

3.     Store in an open topped barrel or compost bin with drainage holes at the bottom for up to 2 years.

4.     Put layers of leaves as your brown material in a compost bin and alternate with green material such as grass clippings, weeds or food waste.

5.     Cover frost sensitive plants which die back in the autumn to protect the plants from winter rain and frosts. You can make a wire frame around a plant such as a banana after the trunk has been cut off, then pack and insulating layer leaves around the stump and cover the stump with a plastic bag.

Which leaves are best to use?

Leaves that will quickly break down include: ash, beech, birch, cherry, elm, hazel, lime, hornbeam, and willow.

Laves that slowly break down include: hawthorn, maple, magnolia, oak, sycamore and horse chestnut.

The best leaves to use are oak, beech and hornbeam.

Evergreen leaves should be shredded first as they take a very long time to break down. They include: holly, bay, rhododendron, photinia and skimmia.

Conifer needles take a very long time to break down even if moistened and turned every few weeks, so they are best used as a mulch over acid loving plants such as blueberries and azaleas.

How do you use leaf-mould?

Some plants such as vegetables, annuals and grasses prefer soils dominated by bacteria so it is best to use compost or well-rotted manure as soil conditioners for these groups. The bacteria quickly break down the organic material which generally has a higher level of nutrients and a lower C:N ratio. Leaf mould contains lower nutrient levels plus lots more carbon locked up in complex substances like starch, lignin and cellulose which fungi tend to slowly break down. So leaf-mould is better used on trees, fruit bushes, shrubs and perennials which prefer soils dominated by fungi. Well rotted leaf-mould should be added to the soil surface of these groups as a mulch in the autumn or spring to help build the soil mycorrhizal fungi. The mycorrhiza will bring more water and nutrients to the plant roots and so help to create stronger, healthier plants.

An alternative use of leaf-mould is to dig it into the soil when it has been partially broken down to raise the humus content of the soil. This is especially useful for heavy clay soils or light sandy soils. As well as improving soil structure by providing more food for soil living organisms it will help the soil to hold more water to enable the plants to tolerate drought better and hold more nutrients bound onto the humus.

Finally leaf-mould can be mixed with sharp sand, garden compost and soil and used as a potting compost.