Australian Plants Society NSWMulch – Mother Earth’s way to protect her plants

We all know about healthy diet and lifestyle. It helps keep us young and stress free. And so it goes with mulch – Mother Earth’s way to protect and nourish herself and stay stress free. Mulch emulates our native forests and bush, with their extensive covering of leaf litter, rocks and mosses.

Natural mulch cover of rocks, moss and leaf litter in a dry sclerophyll rainforest. Photo: Heather Miles

Natural mulch cover of rocks, moss and leaf litter in a dry sclerophyll rainforest. Photo: Heather Miles

Mulch is critical for all gardens, but particularly for native gardens, which are often planted for both beauty and sustainability.

Why does mulch work?

•  It keeps the soil moist enabling plants to keep growing and conserving water
•  It protects the roots from extremes of heat, cold and heavy rain
•  It provides a steady stream of nutrients, particularly nitrogen, as the mulch breaks down
•  It improves the soil structure as worms and fungi proliferate (with organic mulches)
•  It creates habitat for bugs and that attracts birds and lizards and other foragers
•  It slows down the weeds (and that saves our backs and knees!)
•  It makes the garden look more attractive creating more definitive edges.

Woodchip mulch providing soil cover and nourishment for Eremophila ‘Kalbarri Carpet’. Photo: Heather Miles

Woodchip mulch providing soil cover and nourishment for Eremophila ‘Kalbarri Carpet’. Photo: Heather Miles

What kind of mulches are there?

There are three types of mulch:
•  Organic mulch
•  Inorganic mulch
•  Living mulch
Organic mulch includes eucalyptus leaf litter, wood chips, pine bark chips, compost, old lawn clippings, pea straw, stable straw, lucerne, seaweed, hay, manure, sugar cane mulch and paper. Eucalyptus mulch is particularly beneficial in a native garden because it promotes the development of micro-organisms in the soil which enhance plant health.

Organic mulches create appetising habitat for interesting fungi that are beneficial to the soil. Photo Heather Miles

Organic mulches create appetising habitat for interesting fungi that are beneficial to the soil. Photo Heather Miles

Essential soil fungi

Essential soil fungi

Inorganic mulch such as gravel, decorative pebbles, crushed rock and sand. These are particularly useful in dry or fire prone areas, close to the house, or for plants from hotter drier areas that need plenty of drainage. Best to keep away from grass clippings and lawn mowers though!

Pebble mulch creates a healthy environment for the Xanthorrhoea (Grass Tree), Anigozanthos sp. (Kangaroo Paw) and Chrysocephalum apiculatum. Photo: Heather Miles

Pebble mulch is more fire-safe and creates a healthy environment for the Xanthorrhoea (Grass Tree), Anigozanthos sp. (Kangaroo Paw) and Chrysocephalum apiculatum. Photo: Heather Miles

Living mulch includes any low-growing, dense ground cover plant. Not only do they cover the ground, but they look beautiful as well, with their displays of foliage and flower.

Using living mulch has the added results of flowers and interesting leaf texture. Scaevola grows densely with its beautiful fan flowers (left). And Hibbertia pedunculata is a hardy long flowering ground cover that creates similar flowering impact, while covering the soil well.

Where do I get good mulch?

Jeff is fortunate in having two sources of mulch six months apart, thanks to accommodating neighbours: the neighbour on one side has an 80-year old English Oak (Quercus robur) which grows the boundary and delivers an abundance of quick composting oak leaves that Jeff spreads around and uses as mulch.

The neighbour on the other side has a 40-year old lemon-scented gum (Corymbia citriodora) – see photo below, which drops all its bark and every leaf (well, it appears to be every leaf) during the months of December and January. The bark is collected, broken up and used as mulch and the following leaf drop is similarly used. Not only does this provide a great mulch, but there is a faint citrus smell when wet – just like the Australian bush!

Failing accommodating neighbours, some local councils have mulch available free to residents and of course, there are quality landscape and hardware stores that have good mulch.

Jeff’s handy mulch source – his neighbour’s 40 year-old Lemon-scented Gum (Corymbia citriodora) which drops bark and leaves in summer, ready for collection and spreading on the garden. Photo: Jeff Howes

Jeff’s handy mulch source – his neighbour’s 40 year-old Lemon-scented Gum (Corymbia citriodora) which drops bark and leaves in summer, ready for collection and spreading on the garden. Photo: Jeff Howes

How do I apply mulch?

Applying mulch is pretty easy, and it’s hard to go wrong. But here are a few pointers to keep in mind.

1. Before mulching, think through where your native plants come from so you can determine the type of mulch you need, whether organic, inorganic or living.
For example:
•  For inland plants where there is low humidity and low rainfall, a mulch of gravel might be the best option as damp organic mulch may lead to fungal problems with these plants.
•  Similarly, for plants from low nutrient soils, inorganic mulches work well.
•  For rainforest plants, deep and moist green organic mulch would be a better option.

Gravel-based mulch is useful for plants from low nutrient environments like this Stylidium productum which grows in moist soils of sandstone regions. Photo taken at the Australian Botanic Gardens at Mount Annan by Heather Miles.

Gravel-based mulch is useful for plants from low nutrient environments like this Stylidium productum which grows in moist soils of sandstone regions. Photo taken at the Australian Botanic Gardens at Mount Annan by Heather Miles.

2. Before mulching, it is best to remove any grass, weeds and dead plants from the bed. Another option is to lay down many layers of wet newspaper or cardboard over the weeds. This will kill the weeds and then you apply your layer of preferred mulch. It also reduces household waste paper and returns the carbon it contains back to the soil. The planet will breath a sigh of relief every time you do this. (Just be aware that paper can attract termites so best not put close to your house!). If you’ve got plenty of time, just lay your mulch deep enough to kill the grass and weeds and let it sit for 6 months. This is a great approach when your soil is dry and/or compacted, as it lets the earth worms start doing their thing.

3. Consider the type of mulch you are adding and whether any nutrient compensation is required. For example, if you are using dry or woody material such as fresh wood chips or dried leaves, these can deplete the soil’s nitrogen supplies which is used up as they decompose. Simply apply some blood and bone to the soil before spreading the mulch to compensate for this nitrogen loss.

Mushroom compost is variable in its pH and chemical make up and so care has to be applied when applying to our native plants, which are frequently acid loving.

Banksia blechnifolia, a beautiful ground-hugging banksia from Western Australia, growing at Burnley Gardens in Melbourne – this makes a great living mulch and adds textural and colour interest to any garden. Photo: Heather Miles

Banksia blechnifolia, a beautiful ground-hugging banksia from Western Australia, growing at Burnley Gardens in Melbourne – this makes a great living mulch and adds textural and colour interest to any garden. Photo: Heather Miles

4. Next, work out how you are going to water the plants after you lay the mulch. For example, drip soaker hoses placed below the mulch work better than just laying the soaker hoses on top of the mulch. Water applied above the mulch may not always penetrate to the soil below. You can check the soil’s moisture level after rainfall or watering – just dig down to see how far the water has progressed through the mulch. The soil can still be dry even after heavy rainfall – an all too common problem that occurs if the mulch has been applied too thickly or it is very fine and has matted together to form an impervious layer for moisture. If this occurs, ‘loosen up‘ the mulch with a fork or similar and reduce the depth of your mulch.

A mix of pebbles, rocks and Schlerantha ground cover makes an effective mulch. Photo of the Australian National Botanic Gardens in Canberra, by Heather Miles.

A mix of pebbles, rocks and Schlerantha ground cover makes an effective mulch. Photo of the Australian National Botanic Gardens in Canberra, by Heather Miles.

5. Apply mulch at any time of the year, but mid spring or early summer works best as this is the optimum plant growing period. The mulch helps retain the soil moisture and provide a cool root run to speed up new growth. To get the best results from the mulch, ensure the soil is wet or damp before the mulch is applied.

Check out this recently mulched street tree, outside Jeff’s house (below). Local councils are to be applauded for their commitment to sustainability. Many have lists of indigenous native plants (i.e. those from their districts) on their websites, along with lists of ‘drought tolerant’ plants which includes many natives. Here’s a stunning Corymbia calophylla var. ficifolia, one of the grafted flowering gums. It is growing well in its perfect circle of mulch (a deliberate design feature) and flowers prolifically throughout summer.

Recently mulched Corymbia calophylla var. ficifolia, flowering profusely in summer, It’s accompanied by a small grevillea from Western Australia, Grevillea thelemannian, which has lovely pink-red flowers. Photo: Jeff Howes

Recently mulched Corymbia calophylla var. ficifolia, flowering profusely in summer, It’s accompanied by a small grevillea from Western Australia, Grevillea thelemannian, which has lovely pink-red flowers. Photo: Jeff Howes

6. Apply mulch about 75 mm deep, but not more. Mulch applied too thickly causes de-oxygenation of the soil which can kill plants or slow their growth or can prevent moisture penetration as detailed above. After years of using mulch, I have now reduced the maximum depth to about 50 mm as this aids water penetration.

7. Avoid piling mulch up against the stems and trunks of plants as this can lead to trunk rot and your plant dying. This is especially so with plants from arid inland areas.

8. Keep an eye on your mulch and how it is working:
As organic material breaks down, it coats the soil with a wax-like substance which makes the soil, especially sandy soils, ‘non-wetting’ or water repellent. Applications of soil wetting agents are very effective and well worth using to overcome this.

Organic mulch needs to be topped up every 1 to 2 years to maintain desired thickness as it breaks down over time.

How do I use mulch in garden design?

There is plenty of scope when using mulches to mix and match texture and colours to complement your garden design. Below, you can see how hardwood chip mulch has been used as a path highlighter which contrasts beautifully with the more informal mounds of foliage, grass trees and fine eucalyptus leaves.

It evokes a sense of mystery and wonder as people wander through the garden.

Up the garden path in Jeff’s garden. Photo by Jeff Howes

Up the garden path in Jeff’s garden. Photo by Jeff Howes

Mulches also have different colours and so can complement the planting design. Note the complementary colours of the mulch, with its deep mauve-pink leaves and the mauve of the Isotoma axillaris flowers shown below.

Another great design feature is the straight grass edge along the garden, creating a powerful contrast of the informality of the planting and mulch, with the relative formality of the grass edging. Not all Australian native gardens have no grass!

Isotoma axillaris with its pale mauve flowers is complemented by the deeply textured gum leaves and the straight, grass edging. Photo: Jeff Howes

Isotoma axillaris with its pale mauve flowers is complemented by the deeply textured gum leaves and the straight, grass edging. Photo: Jeff Howes

So whenever you think plants, think mulch. Keeps you happy (less watering, fertilising and weeding), keeps the plants happy (moister, easier to grow and stay healthy) and keeps Mother Earth happy.

Happy mulching!

Jeff Howes and Heather Miles

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