Organic mulches have the added benefit of feeding and conditioning the soil as the mulch breaks down. Inorganic compounds such as gravel or black polythene may also be used.
Why mulch?
Mulching will save time as putting a thick layer of material over the soil reduces weed germination.
Light is essential for most seeds to germinate and mulch will prevent light from penetrating to the soil surface where weed seeds are awaiting ideal germination conditions.
Mulching can also reduce the need for watering as it helps to retain moisture in the soil.
However, you must mulch when the soil moisture level is adequate, as anything put on the soil surface will hinder the movement of water into the soil.
Mulching protects the soil and soil organisms (those unseen garden heroes) from any scorching effects of the sun in the height of summer.
Conversely, it will help prevent frost damage to plant roots and reduce any adverse effects of severe frosts.
Spreading it around
Lay your mulch as thickly as possible. However, if you are using a light layer of material you may wish to put down a thick layer of well-soaked newspaper first, as this will help keep out the light.
Be careful not to mound mulch against the base of your plants as this may cause stems to rot.
Pea straw is used extensively in the native plant collection for its protective, moisture-retentive and weed-suppression qualities that are as good as any other mulch.
However, the aesthetics may not be on par with some materials available. The nutrient and soil conditioning benefits of pea straw will more than make up for its more natural appearance.
It is also a relatively cheaper alternative to many materials available which is always a consideration if you have a large garden to mulch. - Shirley Stuart
- Shirley Stuart is curator of the native plant collection at Dunedin Botanic Garden.
