Using Woodchip Mulch in the Garden
What type of woodchip mulch is best to use and where and how to use it in your garden
Previously I’ve written about my anti-swales and how I’ve used woodchip mulch in my productive garden to increase water holding capacity. This post looks at using woodchip mulch in general.
I love mulching. It’s one of my favourite gardening jobs. I love watching as the mountain of a mulch pile slowly diminishes. I love the physicality of filling barrows with the stuff and pushing them through the garden. I love seeing the way it instantly transforms a space to make it look neat and tidy. I love the practical benefits mulch brings to my garden.
Want to sell your house? Get mulching.
Want to make your garden look neat and tidy? Get mulching.
Want to weed your garden less? Get mulching.
Want to get fit? Get mulching.
Want to use less water in the garden? Get mulching.
If you want value for money in the garden, nothing beats investing in spreading a layer of mulch across your property.
Where in the garden should you use woodchip mulch?
With the exception of the vegetable patch, the answer is everywhere! (More on mulching the vegetable patch here).
For what it is and what it can do for your garden, mulch is incredibly cheap. It’s a very low maintenance surface. I use it to suppress weeds and retain moisture in perennial beds such as edible forest gardens. I use it as a ground cover under some of my fruit trees. I even use it on the paths to create anti-swales.
How thick should the mulch layer be?
This is another one of those “how long is a piece of string?” questions. It really depends on your circumstances:
What are you mulching?
What type of irrigation do you use?
How reliable is your supply of irrigation water?
How much summer rainfall do you receive?
My garden receives very low rainfall in summer. But my property has reliable access to water:
Many sheds and buildings capture rainwater in several large tanks.
My property has a bore that provides slightly salty water, okay for irrigating much of the garden.
The property also has a dam.
And if all of that fails, we’re connected to mains water supplied by some of the most reliable reservoirs in Australia.
Because of this situation, I don’t rely on rainfall to keep my garden thriving through summer. Instead, I capture as much water as I can in winter, when it is abundant, and then focus on delivering the water as efficiently as possible to the garden.
I do this by installing drip irrigation on the soil surface and then covering the irrigation with around 15 cm of woodchip mulch. This set-up means that hardly any water is lost to evaporation. A few years back, I set up some of my garden beds this way and then planted into them between Christmas and New Year’s Eve. The plants were mostly tube stock. I carefully tunnelled down through the mulch layer, located an irrigation dripper and then planted the plant. Often it was only the bottom of the root ball that was in contact with the soil.
On some days I needed to plant hundreds of tube stock quickly before the plants dried out in the hot sun, so they went in without much care or attention. I just banged them in. Then I watered them well by hand once and after that they had to rely on the irrigation system. Those small, tender plants were planted at the beginning of a long hot and dry summer, and they were given only minimal irrigation. Every fortnight they were watered for 30 minutes (through drippers with a low 1.6 L/h flow rate). Yet despite this, they thrived. This is because the only way the water could leave the garden bed was via transpiration from the plants. Perversely, the bigger the plants have grown, the more they have transpired and the more water they require to thrive.
Apart from reducing soil evaporation to almost nothing, another benefit of all that mulch is that weeds struggle to take hold. For the first few years I’ve hardly had to pull any weeds from these garden beds. By topping up the mulch layer every second year, I’m also preventing any wind-borne weeds from establishing.
Thick mulch does have a downside
The downside of using so much woodchip mulch is that it takes a lot of rain to infiltrate down to the soil. I know this because when I received a heavy downpour of around 60 mm in February one year, the rain didn’t make it through the layer of woodchip mulch to the garden soil. For me, this isn’t a problem, as the irrigation system is so efficient. However, if you have limited access to water and are reliant on summer rainfall to keep your garden alive, then only a thin layer of mulch (if any) should be used.
Thick mulch can also cause issues for some grasses and other plants that are sensitive to collar rot or crown rot.
The thickness of the mulch layer you spread will depend on your individual circumstances. There’s no rule that says “one thickness suits all” when it comes to mulch.