Using organic mulch is one of the most important things we can do to take care of the soil in our gardens, and grow healthy plants and ultimately healthy people. 

Mulches are materials that are spread on the surface of the soil, and rot down to feed microorganisms within the soil ecosystem, and the plants that we grow.

Why Use Organic Mulch?

An application of the right type of mulch should help us as gardeners in a range of ways. It should:

• Add slow-release fertility to beds or growing areas. 
• Reduce evaporation from the surface of the soil and conserve soil moisture. 
• Increase soil carbon, helping to sequester carbon to fight against climate change. 
• Help to prevent soil surface erosion, run off and compaction. 
• Reduce the growth of weeds, and excessive competition for the plants we grow.

The Main Types of Organic Mulch

There are a number of different types of mulch made from organic matter that we can choose for different applications in our gardens. 

• General purpose mulches – like compost, leaf mould or well-rotted manures.
• Carbon rich mulches – like wood chip, straw, autumn leaves etc...
• Nitrogen rich mulches – like grass clippings or other leafy material. 
• Specific leafy mulches to provide other specific plant nutrients and micronutrients – the leaves of specific dynamic accumulator plants like comfrey, for example, or seaweed.
• 'Living mulch' – companion plants used as ground cover.

Which Mulch To Choose

Which type of mulch to choose depends on the growing area, the plants being grown, environmental conditions and the requirements of specific plants in the area. 

Some mulches, like a home-made compost, for example, can be beneficial as a mulch in most areas in a garden. However, others are best only used in specific circumstances. 

For example, a wood chip mulch is best used only around woody perennial plants – shrubs and trees – and not on its own around annual crops. 

This is because as the woody material begins to break down it actually locks up nitrogen in the soil for a while. Leafy annual plants need nitrogen during key phases of growth, so using a mulch that limits nitrogen availability is not always the best idea. But wood chip can be combined with a nitrogen-rich material to counter this issue.

Nitrogen rich mulches can be wonderful for leafy plants with high nitrogen needs. However, too much nitrogen can 'burn' plants. And in some cases, an excess of nitrogen can encourage leafy growth at the expense of flowers and fruits.

Thinking about the nutrients required for certain plants can help us work out the best materials to use for a mulch around them. Using the leaves of plants which are very good at gathering certain nutrients and concentrating them in their plant tissues can provide specific nutrients at the right times. For example, comfrey leaves spread around certain plants like tomatoes, for example, can be beneficial because they contain relatively high levels of potassium that is required for successful flowering and fruiting. 

Organic mulches are an important part of organic gardening. But learning to use the right one in the right place is crucial for a garden that is as abundant and beautiful as possible.