Urban Food Garden

Mulching Materials

This page lists some of the more common mulching materials available.  It is by no means a complete list, but all the mulches mentioned below are ones that I currently use or have used in the past. 

For information on using mulches on vegetable beds see  The Advantages And Disadvantages Of Mulching Vegetable Beds and Seasonal Staged Mulching Of Vegetable Beds.

key factors to consider

The key factors in determining what are the best mulches for your garden are cost, quality and what is available.   

For example, straw and horse manure can often be obtained for free, but it contains a lot of weed seeds.  Whereas sugar cane mulch is expensive and comes wrapped in plastic, but it is a high-quality mulch that has no weed seeds in it.  There is no best option, rather it is a matter of what suits your needs based on budget and availability.

PROCESSING MULCH

All mulching materials can be spread directly on vegetable beds, but most will be improved if they are processed first.  There are three ways that mulch can be processed to improve its quality.

  • BUYING SPOILT MULCH
    It is possible to buy mulching material (straw, hay, pea straw and Lucerne) that has already begun to break down, either from water damage or age.  This older, poorer quality material is generally easier to spread and breaks down more quickly than than fresh mulching material.
  • PROCESSING MULCH BY HAND
    This involves heaping mulching material in the open to expose it to the elements, turning and watering it to hasten the breaking down process.
  • PROCESSING MULCH THROUGH A DEEP LITTER CHICKEN PEN
    This involves spreading the mulching material in a pen that chickens have constant access to.  As the chicken’s scratch at the material not only will they break it down they fertilise it in the form of their own manure.  This is my preferred method of processing mulch.  For information see Deep Litter Chicken Pen.
sugar cane mulch

When sugar cane mulch first came on the market I was sceptical of it from an environmental perspective.  It comes wrapped in plastic and, given that I live in Victoria, hundreds of kilometres away from where it comes from in Queensland, it is usually has to be transported great distances.  However, it has two big advantages, the mulch is exceptionally fine, so it does not have to be further broken down before spreading it, and it has no weed seeds in it.

Though it rates relatively poorly in terms of environmental impact I have found it useful for mulching pots and as a backup when I run short of my deep litter processed straw and pea straw mulch.

ADVANTAGES SUMMARY

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SUGAR CANE MULCH ADVANTAGES

  • Fine mulch that does not need to be processed before being used.
  • Contains no weed seeds.

DISADVANTAGES SUMMARY

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SUGAR CANE MULCH DISADVANTAGES

  • Comes wrapped in plastic.
  • Has to be transported long distances.

While being the finest mulching material on the market and completely free of weed seeds it comes wrapped in plastic.

straw

This it the mulch that I use the most of, primarily because it is relatively cheap, can be easily sourced locally and contains fewer weed seeds than hay or pea straw.  However, it needs to be further broken down before spreading and is not as nutritious to your soil as nitrogen fixing plant mulches, such as pea straw and Lucerne.  

These days straw is the most common mulching material that I use.

ADVANTAGES SUMMARY

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STRAW ADVANTAGES

  • Relatively cheap.
  • Contains few weed seeds.
  • Easily sourced locally.

DISADVANTAGES SUMMARY

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STRAW DISADVANTAGES

  • Low nutrient value.
  • hard on the hands if you handle it without gloves.
  • Needs to be processed to turn it into fine mulch.

Straw bales are cheaper than pea straw or Lucerne, have few weed seeds and are usually easy to source locally.

pea straw

Pea straw is dried pea bushes after the pea crop has been harvested.  Being a nitrogen fixing plant it has a higher nitrogen content than straw.  It used to be extremely cheap, but as its benefits as an organic mulch became more widely known its price went up considerably. However, it is still much cheaper than Lucerne, the only other nitrogen fixing plant that is readily available as a mulch. But it is harder to spread in its unprocessed form, it needs more processing to turn it into an easily spreadable mulch than most of the other mulching materials.  Like straw and hay, it can contain weed seeds.  But it also often comes with pea seeds. As most of the peas that are grown are not fresh picking peas these sprouting peas in pea straw mulch are a nuisance as they will not grow into anything useful to the average food gardener.

On balance pea straw is quite good as a mulching material. It is the second most common mulch that I use.

ADVANTAGES SUMMARY

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PEA STRAW ADVANTAGES

  • Richer in nitrogen than straw.
  • Cheaper than Lucerne hay.

DISADVANTAGES SUMMARY

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PEA STRAW DISADVANTAGES

  • More expensive than straw.
  • Contains both weed and pea seeds.
  • Hard to spread in its unprocessed form.
Hay

Cheaper than Lucerne and contains more nutrients than straw, but it has some serious drawbacks.  As it is made using mature cut grass it can contain a lot of weed seeds.  An even bigger problem is that some grasses will sprout from the tiniest of pieces, turning into a weed problem.   

To minimise these risks grass hay needs to be heavily processed before being spread on vegetable beds. For this reason I rarely use hay as a mulching material.

ADVANTAGES SUMMARY

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HAY ADVANTAGES

  • Cheaper than Lucerne hay.
  • Contains more nutrients than straw.

DISADVANTAGES SUMMARY

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HAY DISADVANTAGES

  • Can contain lots of weed seeds.
  • Some species of grass hay can sprout from tiny pieces of itself.
  • Is more expensive than straw.

As well as potentially carrying lots of weed seeds some grass hay can sprout from tiny pieces of itself.  LEFT: A piece of grass hay that has sprouted.  RIGHT:  What happens when lots of pieces of grass hay sprout.

stable sweepings

Stable sweepings are mainly made up of straw used for horse bedding in stables, though it may also contain some scraps of hay and chaff.

Its main advantage it that it is considered in the horse industry as a waste product, so gardeners can usually get it for free. It also contains plenty of horse manure.  But horse manure can contain lots of weed seeds embedded in it as such seeds are not killed when they pass through a horse’s digestive system.  Of all the mulches stable sweepings is the most likely to introduce unwanted weeds to your garden.

In the past I regularly used stable sweepings, but in doing so I inadvertently introduced several new weeds to my garden.  So these days I mainly use straw and pea straw as they contain fewer weed seeds.

ADVANTAGES SUMMARY

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STABLE SWEEPINGS ADVANTAGES

  • It is usually free.
  • Rich in nitrogen due to being laced with horse manure and urine.

DISADVANTAGES SUMMARY

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STABLE SWEEPINGS DISADVANTAGES

  • Contains lots of weed seeds.
  • Often comes with other contaminants such as plastic, tape and even the odd syringe.
lucerne (alf alfa)

Lucerne is a nitrogen fixing plant used to make high quality stock fodder.

As it is high in nitrogen it makes it a very desirable mulching material for gardeners.  However, its value as stock fodder makes it very expensive.  Weather damaged Lucerne can sometimes be obtained at a cheaper price but even then it is the most expensive mulching material on the market.

While Lucerne is considered the king of mulches I rarely use it as there are so many other mulching materials around that are almost as good but much cheaper.

ADVANTAGES SUMMARY

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LUCERNE ADVANTAGES

  • High in Nitrogen.
  • Easier to spread in its unprocessed form than pea straw.

DISADVANTAGES SUMMARY

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LUCERNE DISADVANTAGES

  • Very expensive.
  • Is hard on the hands when handling it without gloves.
Lawn CLIPPINGS

Not the easiest of mulches to work with as, if applied too thickly, it can turn into a smelly slimy mess.  It also can contain weed seeds. 

However, if applied thinly it can make a useful mulch.  Its biggest advantage is that, if you are using your own lawn clippings, it is not an external consumable import.  Minimising the number of imported consumables used in a garden is a good environmental goal to work towards.

In the warmer months I routinely spread thin layers of grass clippings, especially on general garden beds.

ADVANTAGES SUMMARY

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LAWN CLIPPINGS ADVANTAGES

  • Non imported consumable, if using clippings from your own lawn.
  • Free.

DISADVANTAGES SUMMARY

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LAWN CLIPPINGS DISADVANTAGES

  • Can be smelly and slimy if applied too thickly.
  • May contain weed seeds.

Lawn clippings spread on a vegetable patch.  If spread thinly they can make a reasonable mulch.

sawdust

Arguably more of a soil improver than a mulch.  Wood cellulose is much tougher than plant cellulose, which means bacteria takes a lot longer to break wood cellulose down.  While doing so the bacteria also breaks down nitrogen, if you spread fresh sawdust on a vegetable patch it will consume much of the soil’s nitrogen, thus making a poorer quality soil.

The only way to use sawdust as a mulch is to break it down until it is almost completely turned into compost before spreading it.  A good way to do this is to first spread it on your paths and leave it there for a good 12 months.  Once it has almost entirely broken down you can then spread it over your beds.  But a WARNING, do not spread sawdust on your paths if you have couch grass in your garden beds.  Couch grass loves to grow in soft soil, sawdust makes an ideal medium for couch runners to spread into.  For more information about Couch grass see Removing Couch Grass.

Another problem with sawdust is that it has become much more expensive and harder to find, particularly hardwood sawdust.  Though sometimes it can be obtained for nothing from larger horse stables as some of them use sawdust in place of straw as horse bedding.  But whatever sawdust you source, make sure it does not contain any treated pine.

ABOVE: Sawdust (with some woodchip particles) on a pathway at the Ballarat community garden.  BELOW: Couch grass spreading into that same pathway.  Sawdust and Couch is not a good combination!

ADVANTAGES SUMMARY

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SAWDUST ADVANTAGES

  • Can double as a cover for paths.
  • Is good for bulking up new soil.

DISADVANTAGES SUMMARY

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SAWDUST DISADVANTAGES

  • Takes a very long time to break down into a usable mulch.
  • Not good as a cover for paths if Couch grass is present.
Lake Weed (only accessible to Ballarat gardeners)

Ballarat has a unique source of mulch in the form of lake weed that is harvested on a large scale from lake Wendouree during the warmer months.  The harvest is dumped in Victoria Park next to Gillies Street South.

The benefit of lake weed to local gardeners is that it is free and contains no weed seeds. But as it is largely made up of water it contains few nutrients and quickly rots down to almost nothing.  You can however sometimes find batches of it that have already rotted down, which means it is more concentrated. 

While I have used lake weed in the past, because of its smell and the fact that it quickly rots down to almost nothing, I do not use it now.

ADVANTAGES SUMMARY

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LAKE WEED ADVANTAGES

  • Contains no weed seeds.
  • Is free.

DISADVANTAGES SUMMARY

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LAKE WEED DISADVANTAGES

  • Quickly rots down to almost nothing.
  • Contains few nutrients.
  • Smells while it is rotting down.

Lake weed piled up next to Gillies Street, Ballarat.  Gardeners can come and collect as much as they like anytime.

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