Using organic mulches is one of the key practices we need to employ to keep our gardens healthy and productive over time.
But if you are new to gardening, you may find this concept confusing. You may wonder why we use mulches, how to use them, and which organic mulches to use in different situations and around different plants.
What is an Organic Mulch?
Organic mulches are layers of material which are placed over growing areas or between your plants to cover areas of bare soil. They are made up of organic matter (decomposed or decomposing plant or animal derived materials).
In a ‘no dig’ system, rather than digging compost or other fertilisers into the soil, these are laid as mulches on the soil surface.
Why We Use Mulches in a Garden
In a garden, we use mulches for a wide range of different reasons.
We can use mulches to:
- Add nutrients and build soil fertility.
- Improve the structure and capacity of the soil.
- Protect bare soil from nutrient loss and erosion.
- Retain more moisture in the soil and help reduce water use.
- Suppress weeds and reduce weed growth.
- Protect plants over winter by providing some insulation for their roots.
Mulches can be specifically chosen to provide one or more of these services. Most mulches will not serve one, but rather multiple functions.
Mulch can also help us increase the biodiversity in our gardens – providing habitat for ground-dwelling wildlife and also helping to improve biodiversity of micro-organisms like bacteria and fungi in the soil ecosystem.
How to Use Mulch
Mulches are often best laid in spring, as the weather begins to warm and precipitation will tend to decrease as we head into summer. However, mulches are often also utilised in the autumn, to protect the soil over the winter months.
It is very important to understand that different situations call for different mulches, and that different mulches can have markedly different characteristics. It is crucial to choose the right mulch for a particular location, and with reference to the plants that are growing in a given area.
Organic Mulches to Use
When deciding which organic mulch to use in a specific location and for a specific purpose, it can be helpful, first of all, to think about four main categories of mulch that you might use:
- Partially decomposed organic matter.
- ‘Green’ (nitrogen rich) materials.
- ‘Brown’ (carbon rich) materials.
- Plants which serve as ground-cover and act as a living mulch.
Partially Decomposed Organic Matter: Compost, Leaf Mould, Well-Rotted Manure
Mulches comprising organic matter which is already partially broken down make great multi-purpose mulches for almost any part of a garden. These can be the backbone of maintaining fertility in your garden – and creating them can be crucial for garden sustainability.
One of the main options, of course, is to make your own compost. The compost you make cannot only be used in pots and containers in your garden. It can also be used to improve the soil throughout the whole of your garden. Making compost should be high on your list of priorities and if you want to grow your own and have not yet started composting, you should do so right away.
Making your own leaf mould is also a great idea if you want to make sure that you work with nature to keep your garden growing strong.
In certain cases, it can also be beneficial to add manure to a garden. However, almost all manures (excepting that of rabbits and certain other small herbivores) must be well-rotted (composted first) before it can be used in your growing areas.
- Add fertility. (Though the figures for homemade compost can vary substantially, typical figures for the three key nutrients nitrogen, phosphorus and potassium are around 0.5% nitrogen, 0.27 % phosphorus and 0.81 % potassium.)
- Are a way to improve the structure of the soil. Adding these types of mulch can improve aeration and the amount of water that soil can absorb. It is also great for making soil more friable, easy to handle, and easy for plant roots to penetrate.
- Boost microbial activity. By adding a good quality compost to your growing areas, adding nutrients and improving the soil, you will also be aiding, and increasing the numbers, of beneficial microbes present there. One added benefit of manure is that it can be even better than compost at boosting microbial life in the soil. This is because it still contains a higher proportion of undigested organic matter than compost – so there is more left for microbes to feed on long term.
Adding a material which is already a considerable way through the decomposition process can be good where you wish to sow seeds directly. It can also look neater and tidier than other types of mulch.
‘Green’ Organic Matter: Grass Clippings, Seaweed, or any other Leafy Green Material
Anything that you might add to a composting system as a ‘green’, nitrogen rich material might also be used as a mulch, to compost in place. Nitrogen rich materials will break down relatively quickly, but are still considered to be a form of slow release fertilizer. They feed the microbial life in the soil as well as ultimately feeding your plants.
These mulches are best used around leafy plants that require a nitrogen boost. But it is important to use caution, as adding too much nitrogen can harm plants, ‘burning’ or even killing them, and too much nitrogen may also encourage certain plants to put on leafy growth at the expense of flowers and fruits.
It is often a good idea to use high-nitrogen materials in conjunction with the carbon rich mulches mentioned below in sheet mulching.
Together, the nitrogen rich and carbon rich materials will fulfil a range of functions and will work together in much the same way that they do in a composting system.
Using ‘green’ mulches is a valuable way to add nitrogen to your garden. But when choosing a mulch, you can further hone in on the specifics of plant nutrients and nutrition to find specific green mulches for specific purposes.
For example, certain dynamic accumulator plants can be beneficial as mulch because they contain higher amounts of specific nutrients, such as potassium, calcium etc.. By choosing the right plants to lay as mulch, you can redress certain nutrient deficiencies over time.
Brown Organic Matter: Woody Material, Autumn Leaves, Straw
Carbon rich organic mulches also add nutrients, but are particularly beneficial for increasing soil carbon, and improving the structure of the soil. A thick layer of one of these mulches can also help keep soil and roots from freezing or cold damage over the winter months, and, in warmer gardens, can also reduce heat stress in summer.
However, especially when using woody material, it is again important to think carefully about how and where exactly you use it. It is great around fruit trees, mature shrubs and woody perennials, for example, but is not necessarily always such a good idea in a vegetable garden. Woody materials breaking down cause nitrogen levels to fall, which is another reason why it can be a good idea to combine brown and green materials when mulching.
The bright idea behind living mulches is that rather than chopping and dropping plant matter, or spreading dead or decomposed plant matter between plants, you use living plants to cover the soil instead.
Using living mulches between other crops is a kind of companion planting. As with any other companion planting, it is important to consider the needs and characteristics of other plants growing close by. Living mulches should complement, rather than competing with, existing plants in a given area.
Which mulches do you use in your garden? Let us know below.
Elizabeth Waddington is a writer and green living consultant living in Scotland. Permaculture and sustainability are at the heart of everything she does, from designing gardens and farms around the world, to inspiring and facilitating positive change for small companies and individuals.
She also works on her own property, where she grows fruit and vegetables, keeps chickens and is working on the eco-renovation of an old stone barn.
To get in touch, visit https://ewspconsultancy.com.