Mulching Your Garden

Mulch is your garden’s best friend. Whether it is for established trees and plants to new plantings or seedlings, mulching your garden is one of the best things that you can do to help with proper growth. Perth has notoriously long, hot and dry summer days. As the temperature rises, so does the need for watering your plants. Most, if not all, of Perth gardening enthusiasts know that mulching the garden beds is as important as watering or fertilizing your plants.

What are the benefits of mulching your garden?

  • Provide protection for the roots of the plants.
  • Prevent evaporation during the drier and hottest months of the year
  • Protect plants from cold, wind and frost during the Winter months.
  • Allow moisture to go to the roots and stop water loss.
  • Reduce weed growth as less light reaches the soil.
  • Prevent erosion of soil and water run offs.
  • Organic mulches break down and nourish the soil.
  • Create a base for microorganisms to grow and help plants thrive.
  • Help reduce diseases.
  • Improve healthy and thriving plants.
  • Visually appealing as it makes the garden look uniform and tidy.

What are their drawbacks?

  • Over mulching can be detrimental for the plants. It suffocates the roots and bury the plants meaning light and water cannot reach the plants. The recommended depth is about 5-7 cm anything more and the plants suffocate.
  • Mulching too close to the base of the plants/trees will attract pests like slugs, snails and diseases that will damage the plants.
  • Some mulches like saw dust can drain the soil from nitrogen making the leaves yellowish and causing poor growth. Counteract this by using a nitrogen based fertilizer.
  • Can cause rot when placed too close to the bark of plants.

What are the different types of mulch available?

Organic mulches: natural, will break down over time and feed the soil and plants.

  • Wood chips: easy to apply and cheap.
  • Grass clippings: from mowing the lawn! Recycle your own grass clippings and help your garden. Let it dry a bot then layer around your plants.
  • Straw, lupin, sugar cane or hay: keeps soil moisture, prevents or stops weeds and supplement organic matter to the soil as it breaks down. Use it around the vegetable patch for a crisp and clean look.
  • Pine needles: fragrant and attractive. Slow degrading and won’t change your soil pH.
  • Compost : recycle your kitchen scraps – you would need a lot of scraps! Or better yet, get it for free or a small fee from your local landfill/recycling facility. Help the environment and your garden.

Inorganic mulches: plastic based

  • Black plastic: can increase the temperature in the soil which can have bad effects on the plants. Good thing is it will prevent disease from affecting your crops.
  • Geofabric: locks in moisture and allows the plants to breathe. Decomposes rather quickly and doesn’t look very appealing! So you can still put a layer of mulch on top.
  • Gravel or pebbles: give the garden a great look, and will not degrade. Create a feature in the garden.

When to apply?

There is no definite time where you can apply mulch. As a rule of thumb do it before the hotter season starts and keep topping up as needed as this will prevent soil erosion, water evaporation and keep the moisture where it is needed.

Hope you had a good read!


Thanks for the informative post.


Pine needles are allelopathic and until composted, can prevent plant growth. In forestry conditions over time they can reduce soil pH.

Raw wood chips cause nitrogen drawdown in soils they are applied to, causing nitrogen deficiencies in plants grown in soils.

Application of uncomposted sawdust as a mulch is not recommended as it will cause rapid nitrogen drawdown. It also will become hydrophobic reducing rainfall penetration/increasing runoff.

Some plants can die if mulch is placed around the base of stems/trunks. It can promote fungal diseases such as collar rot. Unless the mulch is thin or an open matrix (e.g. loose straw), it is recommended that 10cm gap between mulch and stem/trunk be provided.

Some plants can’t cope with organic mulches, e.g those adapted to arid conditions, and such mulches should be avoided as they can cause rots and promote disease.

Another drawback is organic mulches can slowly acidify soils, particularly those which are neutral to slightly alkaline. Sandy and silty textured soils can also become more hydrophobic over time, especially if soils are subject to a drying cycle.


Lots of good advice and thoughts already.

I’m no expert gardener. I’m into native revegetation. Although we do have some plantings that are not around the house yard. For those plants we try to identify the differences between our growing conditions and those a plant prefers. We take the advice of the local nursery where available as to what to do for any new plantings. It mostly works.

For natives we’ve many shared tales of woe from others on similar missions. Most natives are adapted to thrive in our poor and variable soils. Too much fertilising, too much water, too much mulch or the wrong type of mulch can all have an impact. It’s in difference to many traditional gardens where the emphasis is on improving or changing conditions to grow what you like. With mulch less may be better than more. I look to recycle what we have naturally. Mulching away from plants is one way to suppress lawn from invading where the two systems meet. Bracken fern pulled to clear pathways or open up for regrowth is one of my favourites.

Hardwood chips or mill sawdust can be very useful in assisting to re-establish a humus layer in heavily degraded soils. There is no one single rule that says a particular mulching practice is right or wrong. It depends on the need.

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I know people who use sawdust to make paths, it remains essentially weed free for months/years. Eventually it breaks down and they mix it into their compost and replace it with fresh on the paths. I would not use it as mulch.


It works reasonably well for paths if the underlying soil is free draining and retains its load bearing strength when wet. If not, the sawdust path can get soft and boggy. I have also seen it used as flooring in grow tubes (we have wood shavings in ours) where it works reasonably well.

The challenge with sawdust is it has a high surface area (and high carbon source) and it attractive to soil microbes to decompose. Raw or uncomposed sawdust, the soil microbes consume nitrogen from the underlying soil, causing the effect which is known as nitrogen drawdown. It can cause underlying soil to be severely deficient, affecting plant growth. Nitrogen fertiliser (urea, DAP etc) can overcome deficiencies in the long term, but damage may already be done - hence why not recommended as a mulch.

Adding nitrogen fertiliser to raw sawdust mulch could cause hot mulch where the sawdust is thick. The heat can pose problems to plants. Alternatively, the nitrogen is washed into the soil causing other issues.

If it is composted (stable product), it can be used as a mulch…but then again it may have a better use as a soil ameliorant.

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When the Rankine Bros sawmill outside Peeramon on the Atherton Tablelands closed down some decades ago after operating for donkey’s years, all the sawdust which had been continually piled up had decomposed into a very dark mulch.

It was snapped up like hot cakes for use in compost mixtures and was probably one of the most valuable things that the mill disposal sale had on offer.


I found this article interesting but I would like to add some information from personal experience.

Slugs can also be a problem without plants. I had excess sugarcane mulch so last year I put it on a vacant above ground bed. I thought it might enrich the soil. It was thickly laid but I did occasionally turn it. However, recent rain has shown me that this mulch is a slug hotel. I have removed much of the mulch and spread it thinly in other parts of the garden. Now for the beer traps (or vegemite traps) and coffee grounds to try to protect new seedlings in my yard.


I tend to use either wood chip or farm manure mixed with topsoil or peat. Using this means less weeding, and I also try not to walk on it so as to prevent it from compacting. The weather and garden worms do most of the work but I find this certainly improves the soil structure.

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