Mulch Ado About Nothing

It's Autumn & time to mulch. Personally I would like to see the garden get a bit moister before I place another layer on my gardens, but we make do with what Mother Nature gives us.
Mulching is a great time for the garden. I always like the look of everything when its been freshly mulched, all uniform & weed free (for a while at least). If you are going to mulch, it is always a good idea to dig in a 2 - 3 cm layer of compost first. 

What Is Mulch?
Mulch is the term used to describe the uppermost layer of soil. Every ecosystem has mulch in some form - ie in the bush, it is leaves & twigs that protect the soil (remember this when raking & burning those leaves). In the desert, it is sand or pebbles.

Why do We Mulch?
There are four important reasons to mulch. 
1/ The most important reason, in Australia, is water conservation.  Mulch stops the top of the soil drying out, keeps the soil moist, helps stop soil erosion and can reduce watering by about 60 per cent. 
2/ Mulching also prevents weeds and weed seed germination, which compete with plants for moisture and nutrients. 
3/ Mulching keeps the soil temperature constant & helps protect delicate root systems in times of frost as well as searing heat.
4/, Using an organic mulch means you’re adding extra organic matter to the soil & encouraging worm movement in the soil. 

Bark Mulch

Mulch types

Mulches can either be organic or inorganic, but I prefer organic mulches because they break down and add organic matter to the soil. This improves soil structure and drainage, and encourages earthworm and soil microbial activity. 

Organic mulches, such as straw based mulches, are quite common. Try pea straw, but there is also lucerne and bean, and cane type mulches. They can either come by the bale or some people prefer to use the chopped product for a neater look. 

Cube type mulches are also available, such as cubed pea straw which has other ingredients added to it. As soon as this mulch gets wet it forms a softer material. This can be used as mulch, but is better used as a soil conditioner and worked through the soil. 

My favourite mulch is pea straw and I love to use it by the bale because it's easy to use and inexpensive. Simply grab a biscuit and lay it on the garden like pavers. Then loosen it up to fill the gaps.  The only problem with pea straw is the weeds that come with it.

Bark based mulches are another great organic choice. An advantage of the bark based mulches is they take longer to break down so you don't have to apply them as often. They come in a range of grades, from fine through medium, and coarse. It's best to use medium to coarse grade bark mulches because they don't absorb any moisture and allow rainfall, or irrigation water, to penetrate the soil where it's needed. Another problem is that during the natural decomposition of woody materials, such as uncomposted fresh sawdust, pine bark and woodchips, soluble nitrogen is taken from the mulch by fungi and bacteria. This causes something called nitrogen drawdown, but it can be overcome by applying a balanced organic fertiliser before mulching. 


Inorganic mulches, including scoria, gravel and stone river pebbles, don’t break down. These come in a range of colours, are trendy at the moment, and can look effective when used as mulch on pot plants. But bear in mind, if using pebbles in the garden, do it where they will not be littered by leaves and other debris, or it will end up looking messy. Plants with low nutrient requirements, such as many native plants, often benefit from inorganic mulches. Thick woody mulches without leaves are also perfect for these types of plants as they last longer before breaking down and they release very little nutrients.

Stone pebble Mulch

The depth of mulch depends on the type of mulch used. For coarse mulches a layer of between 2 and 6 centimetres is ideal. Although unprocessed straw mulches from the bale can be applied thicker. 

Very fine mulches are to be avoided as they can compact and not allow water to penetrate to the soil beneath. Their fineness also means they are capable of holding a lot of water, once again preventing it from infiltrating the soil beneath.

A good organic mulch is one that is a mix of fine and coarse particles.

Rather than using lawn clippings, leafy prunings and leaf litter as mulch, it's far better to put it in the compost and let it break down naturally. Although some people like to apply compost as mulch, it's actually better to use a coarser material, such as straw or bark. But try putting compost on first, and use it as a soil conditioner or improver, and then add mulch.                

How to Mulch

Take these few steps before laying your mulch down to ensure success.

1. Remove or poison weeds (then wait for a fortnight after using poison)
2. Moisten the soil thoroughly. Ensure that the water you apply is penetrating .
3. If the water is running off the surface, fork through some compost to aid with the water retention.
4. If you are planting into the soil, add some water saving crystals into the planting hole.
5. If you are using bark-based mulches, you might consider sprinkling some blood and bone over the soil. This extra nitrogen will compensate for any nitrogen being taken up by the gradual decomposition of the mulch.
6. Lay your mulch thickly (7-8cm deep), keeping the area directly around plants free of mulch.
7. Lastly sprinkle soil wetting agents over the surface. This will ensure that any watering doesn’t run off the surface of the mulch.

Following these steps will mean you have mulched well.

How often?

Over time organic mulches break down, contributing beneficially to soil structure. Fine mulches will break down quicker than more coarse materials and so will need topping up more often. A yearly top up is usually enough.

The length of time that it takes for a mulch to break down determines how rapidly the plants will be able to access the nutrients in the mulch. Some mulches as they break down may actually take nutrients away from the soil, this effect is only shot-term but in these instances it may be necessary to add manure or blood and bone prior to mulching.

AND my next Blog will be on composting. Oooh I love composting.

Happy Composting & Grubbing in your garden.
Tamara.