The Advantages and Disadvantages of Various Mulches
Leaf Mulch or Leaf Mould
Leaves deposited by deciduous trees in Autumn will mulch soil for you and they will slowly break down to provide organic matter and nutrients to your soil. Leaves do provide the best benefit when composted however.
- good for moisture retention
Use layers no thicker than 8 cm (3 ").
Grass clippings as mulch
- high in nitrogen
- if applied too thickly, you'll get a slimy mess which can heat up and burn plants
- usually contains weed seeds that can germinate in your garden beds
Use layers no thicker than 2 cm (1 "). You can add additional layers however, every couple of weeks.
Ground Cover Plants as Mulch
Plants can be used as mulch as well - these mulches are usually referred to as living mulches. Cover crops can also be used as living mulches.
- annuals provide organic matter and nutrients when they break down
- increases the number of plants you have in the garden, increasing your garden's diversity
- probably the most attractive form of mulch
- can provide food and shelter for insects and other animals and can attract beneficial insects in particular
- some suppress weeds through allelopathy
- very good at reducing erosion
- some (such as those that associate with nitrogen fixing bacteria) provide nutrients whilst they are actively growing
- use nutrients and water
- may not be as effective at suppressing weeds as some other mulches
- take some time to cover bare patches of soil
Living ground covers can be selected to match your garden. Native ground covers can be selected for native gardens. Pumpkins and other squashes are particularly good in edible garden beds. Lucerne is great in orchards. Living ground covers are perhaps the most versatile mulches available.
Newspaper as Mulch
Newspaper should always be covered with another form of mulch such as grass clippings
- adds an extra layer of weed protection
- adds carbon so is useful when using mulches that are high in nitrogen (such as grass clippings)
- if applied too thickly, it will prevent moisture getting to the soil, won't decompose quickly and will keep worms from foraging through the upper layer of mulch
Use no more than 2 or 3 layers of newspaper with up to 8 cm (3") of another mulch of your choice on top.
Make sure the newspaper is thoroughly moistened before you lay the other mulch and don't allow it to dry out - poking holes in the newspaper for improved water permeability is advisable.
Pine Needles as Mulch
- acidic so great for blueberries, rhododendrons etc. which like acidic soil
- also good for neutralising alkaline soil
- don't easily compact
- can't be used around plants that need neutral or alkaline soil
Use layers no thicker than 8 cm or 3 ".
Compost as Mulch
- high fertility so greatly improves the soil by adding nutrients - it also adds a lot of organic matter
- encourages worms
- none really although you may prefer to save your compost for incorporating into the soil where it will add more nutrients to the soil (when used as mulch, some of the nutrients are likely to be washed to other parts of the garden)
If using compost as mulch, it's often better to use it underneath another type of mulch.
Use layers no thicker than 8 cm (3 ").
Sawdust as Mulch
- sawdust is often acidic (though it depends on the wood it's from) so it's great around acid loving plants (blueberries, rhododendrons etc.)
- thick layers can exclude water and oxygen
- it may temporarily reduce soil nitrogen so use it on fertile soils or on garden beds that are growing light feeders
Never use sawdust from treated pine - it contains toxins and carcinogens.
Never use layers more than 8 cm (3 ") thick.
Aging sawdust for a year can help neutralise it.
This is usually made from recycled tyres etc.
- recycled materials
- good weed suppression
- doesn't improve your soil by providing nutrients or organic matter
- there is still concern over leached heavy metals and other toxins from tyres
Use this mulch in layers up to 10 cm (4 ") thick.
It's good on paths and around children's play equipment and garden swings etc. however I wouldn't recommend it on garden beds.
Pebbles, Rocks and Stones etc. as Mulch
- these mulches come in a very wide range of colours, sizes and styles
- store heat during the day and release it at night so really good for frosty areas to protect sensitive plants
- they can be dangerous if they get hit by a lawnmower
- don't provide nutrients or organic matter to the soil
Apply in layers up to 10 cm (4 ") thick.
These are good mulches to use in rock gardens.
Landscaping fabric/ weed mat etc.
- very good weed suppression
- lets air and water through
- does not improve the soil by providing nutrients and organic matter
Black Plastic as Mulch
- excellent weed suppression
- soil is deprived of water, light and air, which can cause a lot of root damage
- no nutrient benefit to the soil
I would never recommend using black plastic as a mulch but it can be done.
Bark, Wood Chips etc. as Mulch
- comes in a variety of shapes, sizes and colours
- some barks and woods have allelochemicals that inhibit plant growth
- these mulches will take nitrogen from the soil initially so should only be used on fertile soils or where light feeders are being grown
Adding compost before such mulches will greatly improve their affects and will also provide nitrogen for the bacteria that break down the mulch.
Use 10 cm (4 ") layers.
Straw as Mulch
NB Hay (other than lucerne hay) contains far more weed seeds than straw so is best composted before use as mulch. Though you can use it in the same manner as straw if you want.
- provides better insulation than hay
- can still contain some weed seeds
- will initially use nitrogen from the soil to break down (so only use on garden beds that have adequate nitrogen or are being used to grow light feeders)
If you have chickens, their bedding straw is a better source of mulch as the chickens will gobble up any seeds still in there and will add nitrogen in the form of manure.
Use 10 cm (4 ") layers.
Lucerne Hay, Pea Straw etc.
- these plants are nitrogen fixers so using them as mulch provides nitrogen to the soil
- also provide other trace elements
- less weed seeds than other straws
- can be expensive
The good news is you can grow your own lucerne and slash it for mulch - you can also use your pea plants once they've finished producing peas. The same can be done with bean plants.
Use layers 10 cm (4 ") thick.
These mulches are particularly useful for plants that are heavy feeders.
A Couple of Interesting Mulches you can Use
Dandelion leaves: yes they're a weed but if you already have them in your garden and have trouble getting rid of them, at least you can use the leaves as a mulch or liquid fertiliser (make tea with them). Dandelions are deep rooted, which is why they are hard to remove but it also means they bring up leached nutrients so the leaves are packed full of goodies for your garden.
Dock leaves: same deal - they're a weed but are deep rooted so if you already have them, you can use the leaves as a mulch to benefit your soil.
Just don't let either of these go to seed otherwise your weed problem will get worse!