Mulching is an important technique in caring for our soils, it can be carried out in a variety of ways that are often adapted to local soil conditions and availability of materials. The previous blog spoke about multiple issues within our current agricultural practices and mulching is one of the solutions that can be applied to both rebuild and retain the health of our soils. It can also help reduce the amount of weeding that needs to be done, it’s a win-win!
In permaculture we are always aiming to mimic nature as closely as possible, especially when it comes to land based design and practice. It is therefore best to mulch when nature mulches, in autumn. When the trees drop their leaves in autumn and the plants die back they leave a natural mulch on the soil. This mulch has multiple functions; the foliage slowly breaks down over time adding nutrients to the soil; the cover protects the soil from wind and rain erosion as well as keeping heat in; the cover also helps to lock moisture in. As mentioned in the previous blog, soil in the UK naturally needs to be covered for all of these reasons and leaving soil bare increases the risk of erosion. You will also find that bare soil becomes quickly covered with weeds as it tries to protect itself. If kept bare for long periods of time erosion is inevitable. Mulch can help to protect as well as restore, build and maintain soils.
So how do I mulch?
There are multiple ways to mulch however the premise for each method is the same. The soil is covered in at least one layer of organic matter that works to fulfil three functions. Adding nutrients to the soil, locking in moisture (preventing runoff) and weed suppression. There are four different types of mulches, organic matter mulches, non-organic mulches, living mulches and green manures. While it is best to mulch in the autumn you may also want or need to do this at different times of year. It is worth bearing in mind that while mulching can lock in moisture and help retain heat it will take longer for the warmth of the sun to reach the soil, which might not be desirable, especially in springtime. The weight/number of layers you need will depend on what you are growing and the time of year that you are mulching. Heavier mulches are useful for perennials however annuals will often require a lighter mulch. Charles Dowding recommends using completely finished compost on his annual no-dig beds as it is light and doesn't attract slugs or snails. However, if you're leaving an annual bed fallow for a season or over winter you might want to use a heavier mulch that will break down before you want to replant.
Organic Matter Mulches
Probably the most common form of mulching that you will see are mulches using organic matter. There are a variety of different combinations that can be used and people often get very creative with available materials and layering techniques. As with many things, observation, experimentation and experience will go a long way in creating a perfect mulch for your soil.
A good starting point is to think about what your soil needs and the plants that you are planning on growing. For example, you may have a soil that is low in potassium, in which case you might want to use ash for one of your layers. It’s also a good to use materials that are easily available to you. For example, if you have lots of easily accessible cardboard waste it can be used as a weed suppressant. A very simple example of mulching would be cardboard covered in wood chip. A more elaborate approach might include a layer of compost, ash, newspaper and wood chip.
It is worth noting however that cardboard, newspaper and wood-chip might contain unwelcome guests, such as toxic glues, inks based on genetically modified plants and diseases. As with anything, it is important to be aware of the source of the product you are using as well as taking into account what is available to you. The solution you come up with may not be as perfect as you would like, but aiming to hit the ‘sweet spot’ of the permaculture ethics will help you make the best decision you can.
Non-organic matter mulches
You may also choose to opt for non-organic mulches such as mypex, which is a semi-permeable membrane that suppresses weeds while letting moisture through. Personally, I am not a fan of this material as the fabric is made from energy intensive plastic and has a habit of fraying. However, it is useful and it may be the most appropriate material depending on your situation. For example, market gardeners may find it useful and necessary to keep perennial fruit bushes weed free. If you do opt for this type of ground cover the best way to cut it is with a blow lamp which seals the edges of the fabric at the same time as cutting; using scissors is more difficult and often results in strands of plastic in the soil. It is also important that the plastic is maintained and not allowed to embed in the soil, it is a nightmare to pull out!
Another common non-organic mulch option is old carpet fabric. As most carpets are now made from Polypropylene this type of mulch does have the potential to cause problems. While it could be useful in the short term, over long periods of time the fabric disintegrates and ends up in little pieces within the soil. If you do choose to use carpet for mulch (or especially to line ponds) it would be better to source pure wool carpet and dispose of plastic based carpet at your local recycling centre.
Green manures can be a great solution for mulching and feeding as they are dug back into the soil immediately. They are usually sown in Autumn and dug into the soil the following spring however they can also be used during intervals between crops in the summer season. They have an obvious disadvantage of disturbing the top layer of soil so if you’re a ‘no-digger’ other mulches might be a better solution. Green manures can be mulched over with organic and non-organic mulches however they will take time to kill so you need to assess whether the type of green manure you are using is suitable for your gardening practice and time frame.
Living mulches are plant mulches that often have the added properties of improving the soil structure and attracting beneficial insects. In contrast to green manures, these mulches are left to grow in a way that is beneficial for the main crop. They can be grown both underneath crops or between crops. For example, at my allotment I am currently growing clover on the paths between the beds as a mulch. Each time I weed I use shears to cut the surrounding clover and lay the clover on-top of the newly weeded bed to cover the exposed soil. It has the advantage of suppressing the couch grass while providing flowers for the bees and nutrients for the soil.
The risk with using green manures and living mulches is that they can be a haven for slugs and snails. I have certainly noticed many of them in my clover patches, they’re not causing too much bother for now, but it’s something to consider.
written by Sarah Davenport