Living mulch: waterwise, firewise and seriously good looking

Mulching the garden to cut-back on water-use is enshrined in garden lore. Protecting the soil from direct sunlight prevents it from getting hot and so reduces evaporation of precious soil moisture. Nothing beats a thick layer of Lucerne or Pea Straw in a veggie garden to keep the soil cool and moist in summer. And bush mulch or wood chips are champions of native and ornamental gardens for improving water efficiency and soil quality.

Unfortunately, the use of organic mulches has a serious downside. The CFA argues that flammable mulches such as straw, chips and leaf litter should be avoided within the defendable space around a house as they can all ignite from ember attack during a bushfire. For this reason, gravel mulches are increasingly popular as a non-flammable mulch solution. But over time, gravel accumulates a layer of leaf litter that is difficult to rake up and in turn becomes flammable. Also, gravels don’t give anything back to the soil (via litter decomposition and nutrients), they have no benefits for biodiversity and they come at a financial and environmental cost.

So, what do we do if we don’t what our homes to be surrounded by a hot and harsh paved desert? An alternative to chips, straw or stone is to use plants themselves. Many native Australian ground covers have foliage of low flammability and are lower fire risk than organic mulches. Ground covers that function as ‘living mulches’ are increasingly popular in naturalistic landscape design, because they provide a long-term, sustainable solution to weed suppression and erosion control. They are a beautiful addition to landscape plantings and provide habitat and food for garden birds and insects. Further, a living mulch improves soil health through litter decomposition and by keeping soil cool, moist and alive. Another advantage of living mulch over organic mulch, is they don’t decompose so don’t need to be replaced every year.

While living mulches can compete with other priority plantings for soil moisture and nutrients, living mulches do have positive effects on soil moisture balance because plant roots enhance water percolation deep into the soil, creating deeper reserves of soil moisture than organic mulch. Because living mulches also produce litter they promote soil life through nutrient cycling. If you are concerned about competition between your living mulch and other plantings, choose low water-use plants for your living mulch that aren’t highly competitive and combine plants with different rooting depths so they access water in different parts of the soil profile (e.g. combine deep rooted trees with shallow rooted ground covers).

Overall, there’s a net benefit to using living mulch in ornamental gardens; especially because a green oasis around your home will improve your personal capacity to cope with a long hot Summer.

Here are some of my favourite native ground covers. All species listed are low water-use and low flammability (i.e. they don’t burn readily or they slow the passage of a fire). Please remember that no plant is completely inflammable and all can burn under the right conditions. Some watering during extended dry or a heat wave will keep plants actively growing and this will improve their fire-retardant qualities

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Cut-leaf Daisy (Brachyscome multifida)

Feathery foliage and cheerful flowers through most of the year; grows in semi-shade to full sun, requires some moisture. There are many varieties with flower colours ranging from white to purple.

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Kidney Weed (Dichondra repens)

Fresh green, kidney shaped leaves carpet the ground and spread by creeping stems. Best in shade but can tolerate full sun if soil is moist; will come back after near death during drought.

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Inland Pigface (Carpobrotus modestus)

Succulent foliage, pink flowers from September to October; part-shade to full sun. Slower to establish and spread than Karkalla (pictured below), makes it easier to manage in the garden.

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Karkalla (Carpobrotus rossii)

Succulent foliage, tolerates part shade to-full sun; drought tolerant once established; covered in bright pink flowers from September to January. Can grow and spread vigorously (Karkalla is in the foreground of image)

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Ruby Saltbush (Enchylaena tomentosa closeup)

Succulent grey coloured foliage; very drought tolerant; grows in semi-shade to full sun; pretty, bright red or yellow edible berries. Prostrate and shrub-like forms are available.

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Creeping Boobialla (Myoporum parvifolium)

A fast growing and drought tolerant plant, white star flowers in Spring and Summer; vigorous, rejuvenate with a hard prune.

Article by Cassia Read. First published in ‘The Watering Can,’ Western Water’s garden e-news, Winter, 2018 and also in Sustainable Garden Australia’s website https://www.sgaonline.org.au/living-mulch-waterwise-firewise-seriously-good-looking/

 


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