Like many things in permaculture design, the use of mulches takes its cue from what we observe in nature. As long as there have been forests, there have been layers of fallen leaves and other organic material that have covered the ground and slowly decayed.
Organic mulch plays an important role in permaculture gardening. It is one of the primary ways to save time and energy digging the soil in garden beds, but it offers a number of other benefits besides. Mulch is a very effective way of slowing down the evaporation of moisture from the surface of the soil, enabling the soil to retain more moisture, which can then be used by plants and microorganisms. Conversely, it can also prevent the soil from freezing in the winter months, helping protect plants. Organic mulch also provides the soil with nutrients as it breaks down, while suppressing weeds.
There are many options of materials you can use as mulch, including inorganic ones such as plastic sheeting. However, among organic materials there are a wide range of choices each with different characteristics and suitability for different growing conditions. Here is a selection.
Straw is commonly used as mulch because it breaks down quickly, and can be piled high on beds because its structure mean that it doesn’t mat down and prevent oxygen and water getting to the soil. Usually, straw is used as winter mulch around trees and summer mulch on your vegetable and fruit beds. Wet your straw to prevent it from blowing away, but don’t make it sodden as this can promote slug activity.
Straw that comes from the bedding at local animal facilities, such as farms and riding stables, which contains manure can give an added nutrient boost to your mulch. However, ensure the source has not used herbicides, pesticides or fungicides in the stables or barns where the bedding has been used. Straw is preferable to hay as mulch as it does not contain seed heads that, if using hay, can germinate in your permaculture plot.
Products such as bark mulch, wood chips and sawdust are all viable mulch materials, but are all low in nitrogen, so are best used in areas where weed suppression is the aim rather than supplying nutrients to plants. Using wood products as mulch on paths can be useful to keep weeds down and to allow the wood to decompose enough that it becomes compost that can be added to vegetable garden beds. Avoid wood products from any source where they have been treated with inorganic coatings.
Newspaper is abundant, cheap and very effective at suppressing weeds. Make sure you water the paper well when you lay it, and keep it damp, particularly in summer, to stop it blowing away. You can combine newspaper with another mulch over the top to crate a more aesthetically pleasing bed. Avoid placing any colored or shiny paper products on your garden beds, as these can contain heavy metals that can be detrimental to plant growth.
Cardboard should be treated similarly to newspaper when used as mulch, but is arguably even more effective as a weed suppressor. Corrugated cardboard is preferable as this allows for good airflow. Worms also seem to like devouring cardboard, turning it into rich humus. Avoid any cardboard that has a plastic coating.
Leaves that have fallen from deciduous trees make a good mulch for weed suppression and the provision of trace elements to the soil. Ideally the leaves need to be shredded to prevent them blowing around in the wind, and should be applied in a thin layer – about 2 inches deep – to avoid them becoming matted, which can prevent proper aeration of the soil. Alternatively, place fallen leaves in a compost bin to partially rot before using as mulch.
Lawns rarely feature in permaculture plots, as they do not provide a yield and grass competes with crop plants for moisture and nutrients in the soil. However, some plots may have wilderness or pasture areas that provide a source of grass clippings, and these can be effective mulch. Grass clippings are high in nitrogen, an essential element for all plant growth. They decompose relatively quickly, particularly in warm weather. This can be very useful if mulching in early spring when giving juvenile plants a good dose of nutrients helps them establish themselves, but is less suitable for long-term mulched beds. Ideally, if using grass clippings for mulch, they should be layered thinly to prevent matting and odors forming, and reapplied regularly. If you get grass clippings from an outside source – a neighbor with a lawn, say – check whether they have used any inorganic lawn fertilizers or herbicides on their lawn before applying the clippings to your beds.
Needles from evergreen trees are a hardy mulch that will only need to be renewed annually. They allow for good water percolation and do not mat together, so the soil remains well aerated. Pine needles are also good for weed suppression and adding carbon to the soil.
The hulls that are a by-product of buckwheat, cocoa, rice, cottonseed, and other grain crops can be used as mulch. They are very slow to decompose, so add little in the way of nutrients, but they are effective if increasing water percolation is your aim. However, being very lightweight, you will typically need to combine the hulls with another form of much, such as straw, to prevent them from blowing away in even light winds.
Like anything on the planet, stone decays, but in comparison to other mulch materials it does so very, very slowly. So stone mulches, including gravel and crushed rock, are not used to provide the soil with nutrients. Rather mineral mulches can be useful for weed suppression and water permeability. They are very durable forms of mulch, and need to be topped up only infrequently, but their ability to absorb and radiate heat can have a detrimental effect on plants.