Mulches are essential in our dry climate and contribute to a more waterwise garden. For further information on the different types of mulch please also see A Guide to Mulch Types.
Apply your mulch in early summer. This will assist in retaining the moisture from the winter and spring rains in the soil longer by reducing evaporation.
A layer of mulch helps suppress weeds, retain moisture, and moderate soil temperature.
Note: Be aware you do not create an impenetrable layer of mulch from years of adding it to the garden and then finding it has not decomposed properly. In this situation the soil can become so matted that nutrients and water can’t penetrate to the roots, and the plants will suffer.
If you believe the old mulch has not decomposed and has become too thick (it should be less than 80mm) remove some before adding a new layer. You may also wish to add suitable animal manure, or blood and bone, and water it in.
- Garden fork or shovel
Step 1 – Always remove any weeds before mulching. If possible use a garden fork or shovel to lightly break any soil crust that may have formed.
Note: If you are using bark or wood chips be aware that some bark and wood products may cause the plants to turn yellow. This is caused by bacteria taking the nitrogen out of the soil to break down the organic material, see A Guide to Mulch Types for further information.
In this situation you can either:
- Leave the material out in the weather for several months to allow the toxins to leach out; or
- Add nitrogen to the soil before adding the mulch. After you have broken the soil crust (as described above) add suitable animal manure, or blood and bone, and water it in.
Step 2 – The type of material you are using will determine the depth of the mulch layer. Fine material such as compost or a mixture that contains a large amount of fine material such as shredded green waste, can applied approximately 30mm thick. See A Guide to Mulch Types on using fine material. Although the fine material will hold moisture it can also act as a barrier.
Coarse and chunkier mulch such as pebbles, wood chips and barks should be applied around 50mm – 70mm thick. Note: If it is too thick water may not get through.
Step 3 – Keep the mulch away from the stem or trunk of the plant. This will help prevent collar rot disease.
Step 4 – If you are using quick rotting mulch then you should re-apply the mulch annually. Hardier mulches can also still be checked annually and added to if necessary.
A Guide to Laying Mulch,