Mulch is a big topic these days with so many people starting to grow food in their back yards. While this is fantastic, there is some confusion about what mulch is suitable, and what negatives a mulch type may have.
We go into some depth on ten types of mulch and what to look out for if using them.
What mulch can do for your backyard garden.
The best thing mulch can do for your garden is to promote soil life. This in turn benefits all plants in multiple ways, but it all starts with a generous laver of appropriate mulch for your situation.
The benefits of mulching a garden can be a large decrease in watering requirements, less weeding because the soil is covered, and it can be a slow release fertilizer in some situations.
This last benefit is through increased biological activity created by the retained moisture, and the cool dark conditions at the soil surface that suit microbial life forms.
It will decay in time, and the question has been asked about what to do with the remnant mulch if fresh layers are planned. This post details some reasoning on how to approach this. It is titled “How often should you replace mulch, can I add to it?“
What kinds of mulch are ok to use in a garden?
There is a long list of suitable materials that will act as a good mulch, and it can be simplified by saying a mulch that is ok to use should be a natural material free from harmful chemicals and has potential to last for a year at least, on average.
The following is a list that we know to be suitable, and each item will be expanded on further below.
- Straw and/or Hay.
- Bark chips.
- Wood chips.
- Wood shavings.
- Coconut husk.
- Shredded paper.
- Cardboard.
- Old cloth and material.
- Pebbles and/or stones.
- Leaves and fronds.
1. Using straw or hay as mulch.
This is a regular go-to ground cover for many of us. It is usually easy to get, and a bale will cover a good patch of ground. It allows water to penetrate without issues and will not settle and flatten. It allows plenty of air flow, and can reflect heat if the color is a pale one.
Negatives of using straw and hay are it can be a fire hazard in very dry situations. It can easily be blown around if it is not watered down well after putting it on the garden. It can be very stiff and be difficult to place around seedlings.
It is pH neutral if my memory serves me correctly.
2. Bark chip as mulch.
Bark chip is a good heavy mulch well suited to trees and larger plants.
It lasts well, and covers the ground effectively. It holds moisture well, and as it breaks down over time, the soil structure benefits from added humus and from the weak acids that form as the bark decays.
Because of the retained soil moisture it is common to see worm activity near the soil surface if the bark is lifted temporarily. This activity promotes root growth in plants and in turn helps with decompaction of hard soils.
Negatives of bark chips are that it can create anaerobic conditions if placed in too thick a layer that may become compacted. Some barks can potentially affect the soil pH if the bark is applied continuously over many seasons. This may be preferred in a blueberry growing situation. A single application should not affect soil pH.
3. Using wood chip.
Wood chip is a great mulch around larger plants ands shrubs. It behaves similar to bark chips but can contain more nutrients if the chips include the cambium layer of the chipped tree.
This layer will break down faster as a mulch but will also feed the soil with the nutrients that were held within it as the tree was chipped.
Negatives with wood chip are it could attract termite activity in some cases. It can also contain allelopathic properties or eluates that will inhibit seed germination and plant growth. It could be used as a weed control mechanism if care is taken.
Only certain species of trees contain these chemicals and are several are presented in the table below.
| Species | Wood chips | leaves | Water solubility |
|---|---|---|---|
| Red Maple | yes | yes | yes |
| Swamp Chestnut Oak | yes | no | yes |
| Red Cedar (juniperus) | yes | yes | yes |
| Neem | yes | yes | yes |
| Magnolia | yes | no | yes |
| Black Walnut (juglans) | yes | no | yes |
| Bamboo (many varieties) | ? | yes | yes |
4. Wood shavings as a mulch.
This is a terrific mulch that is a kind of middle ground between the hard mulches and the soft ones like shredded paper. It will not be common to many people but I have mentioned it because if you can get hold of some it is really impressive stuff.
“Growing lots of ginger, is this the best mulch?” describes how we grew a tremendous amount of ginger just with wood shavings as mulch.
5. Mulching with coconut husk.
This type of mulch is very localized and so is not common. It is more often used as growing medium for pepper vine and also vanilla vine. It can be effective as a mulch.
6. Using shredded paper.
This is often used as a mulch in the backyard vegetable garden. It can be effective if the paper is not printed with inks that can contain problematic chemicals. There has been a move away from the toxic ink versions to more natural soy based inks.
Negatives of shredded paper is the speed of decay. It will break down very quickly and while this is an issue for a garden bed that holds flowering shrubs, it can be a benefit in a vegetable garden. It can blow around if not watered down after placing it.
7. Cardboard as mulch.
Cardboard is a great mulch with several uses. It can be used as a weed suppression mat below stone covered pathways. It ca also be a good mulch beneath garden beds if holes are punched through it all around, and this allows water to pass through.
It will last a season, and then the garden will need a top up of mulch.
Negatives of using cardboard are the flip side of the above. If no holes are made in the cardboard as it is placed in the garden bed, it will likely form a barrier that will keep the bed dry and the plants in that bed may suffer from lack of water.
It will also suppress biological activity. We had someone look after our house for 4 years while we were away in another state of Australia and while we were away they used cardboard almost exclusively through the gardens.
The cardboard rotted down wonderfully but because the cardboard came from boxes and had been taped up with packing tape, this is now still found in places after ten years.
8. Old cloth as a weed-mat and mulch.
Cloth made from natural fiber is good for mulch but should be used in conjunction with another type of mulch spread over the top to hide it. Wood and bark chips will partner well.
Negatives are dyes that may be contained in the material. Some confusion as to the materials fiber makeup may cause some people to use plastic based materials and over time these can break down and enter the environment in fine particles.
9. Rocks, stones, and pebbles.
These are suited to pathways and the like. They are a great mulch that has a long life, they will help with moisture retention, and seeds from many plants do find this mulch a great place to germinate.
We actually have this happening here where we live, and the number of useful plants that come up from the stones is surprising.
Negatives for pebbles and stones is the habit of becoming a heat sink during the hot part of the day. Those of you in the colder climates can use this attribute to store heat in selected areas to help protect cold sensitive roots of some plants.
10. leaves and fronds.
We live in the wet tropics of Australia and we have bananas, gingers, cardamom, arrowroot, and other large leaf plants all through the yard. They make a good mulch because the cover the soil well.
They last for months and hold a good amount of silica which is handy as our tropical soils leach a lot of nutrients through heavy rainfall.
Negatives of this mulch is it can be a little untidy at times. It can also hold water in puddles above the ground and this can be a breeding ground for mosquitos.
We cut the leaves in several places to avoid this. You can also run them over with a lawn mower; and this post “simple ways to make cheap mulch” details the process.
Are some materials dangerous to use as mulch?
For a while now some local bodies have used shredded vehicle tires as a mulch in kids playgrounds. This could be a concern if you were to use this on your garden.
There is debate on the safety aspects if food is grown under this material. We have no knowledge of any particular chemical, and being organic growers here at home, we personally will not use it.
This material will take a long time to decay, decades in fact. It is along time if it turns out to be a source of toxins.
We choose to use only natural materials that we know will break down through biological activity that benefits both the soil and the plants.
Conclusions.
What we have learned over the last 7 years since beginning our permaculture based lifestyle is that the one true constant that we can depend on is the biological activity that comes with a moist garden.
If you get this in place, there is little more to do than steer the whole garden in the direction you prefer. The growing is best left to the natural systems, without the chemical inputs that are so pervasive these days.
NB: If you go to the search icon at the top of the page and enter “mulch” you will have all the articles we have on site all in one place.
Article by Tim Blanch for TheTropicalHomestead.com. He is a qualified Permaculture designer.
*study link “Evaluation of Allelopathic potential of wood chips”