Mulch
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Mulch in the garden is like 30+ sunscreen to us humans. It is strongly recommended because it suppresses weeds, retains moisture in the earth, keeps plant roots cool and protects the soil against compaction and erosion. If leaf mulch or other organic composts are used the mulch provides an additional benefit: as it breaks down the mulch supplies a steady stream of nutrients to the plants.
Types
In terms of their properties there are two categories of mulch: organic mulches that add nutrients to the soil as they decompose and gravel mulches that are used for their decorative appeal in more formal situations.
Organic mulches
These include composts, leaf-mulch, composted manures, straw, wood -chip, and pine-bark and pine-flake.
Gravel mulches
These include pebbles, quartz chips and volcanic scoria.
How to calculate the amount needed
To calculate how many cubic metres (m3) of mulch you will need, you will first have to approximate the surface area of soil that needs to be mulched.
The surface area of each garden bed can be calculated by multiplying the breadth of the bed by its length. Use average measurements for beds that are curved or oddly shaped.
Add the surface areas of all the individual garden beds to arrive at a single measurement in square metres (m2). The following guide will help you to calculate the volume of mulch you will need.
Volume of mulch (m3) = area of garden (m2) x mulching factor
| Type of mulch |
Mulching factor |
| organic |
0.10 |
| gravel |
0.06 |
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Depth of mulch
Mulch should be applied liberally. A thin skin of mulch will do little to protect the soil and will soon develop a threadbare appearance as it breaks down. Mulch needs to be deep enough to inhibit weed growth and ideally should be maintained at a depth of between 50 mm and 75 mm. Organic mulches should be applied at an average depth of 100 mm to allow for settlement back to 75 mm. Gravel mulches should be spread at a depth of about 60 mm. It is a good idea to lay weed mat over the soil prior to spreading gravel mulches to prevent the gravel working its way down through the soil.
How to apply
Use a wheelbarrow or bin to move the mulch from the stockpile to the garden and place it in mounds at regular intervals. Continue t o place the mounds evenly throughout the garden until the stockpile has been used up. Now spread the mulch out using a rake or spreader until the depth is even. Avoid mounding the mulch around plant stems as this could cause fungal problems.
Sweepings
When you sweep your paths, collect the soil, leaves, twigs and other debris in a box or bin and spread it over your leaf mulch. If you are designing a new path, keep it raised above the garden bed so that the path can be swept straight into the garden. This makes for a very low maintenance, easily cleaned landscape.
Autumn leaves
If the quantity of autumn leaves is too many for the size of your garden, compost the leaves for use as a mulch at a later date.
Potted plants
Mulch your potted plants as you do your garden plants. The same benefits apply.
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