Mulching

Is Ramial Chipped Wood Mulch a Nitrogen Thief?

When I was a teenager, my parents bought a house in Sainte-Foy. The garden was in rough shape. The backyard was almost entirely made of asphalt. Perfect for playing basketball! Those who know my father, Larry, will know that we didn’t play for too long and the asphalt was soon torn up to be replaced by lush gardens. After planting, of course, we installed mulch. Everywhere.

“Mulching” is one of the basic elements of « laidback gardening. Mulch typically consists of a layer of plant material about 7 to 10 cm (3 to 4 inches) thick, placed between the soil and the air, to create a barrier between the air and its drying effects – and also against the weed seeds it carries – and the soil where your plants’ roots are growing.” Larry Hodgson, The Benefits of Mulching.

Ramial wood chip. Photo: arpent nourricier

Ramial chipped wood (RCW)

What mulch did we use? Rameal chipped wood of course! After dead leaves (free mulch put on your garden without any effort, what’s not to like?), my favorite mulch is ramial chipped wood. What is it? Simply shredded hardwood branches. Fungi and microorganisms, including bacteria, love to eat it and break it down, enriching the soil in our gardens and improving its structure.

I remember spending an entire summer (maybe my teenage memory isn’t quite right) spreading this mulch all over the place. The 12 wheelers would unload it at the front of the house and I would haul it into the backyard with a wheelbarrow and spread it all over the yard. Since then, it has been my mulch of choice.

Image: freesvg.org.

Nitrogen Thief?

Afterwards, I was often told that the use of ramial chipped wood would use up the nitrogen in the soil to decompose it. This would steal nitrogen, one of the basic elements our plants need for growth. It’s not a ridiculous idea… For the fungi and bacteria in the soil to do their job breaking down the mulch, they do need nitrogen. I started to have doubts. Especially since some horticulture professionals had told me this idea repeatedly.

The truth about ramial chipped wood

So, what about it? Is ramial wood good or not? The reality is that, yes, as the shredded branches decompose, they do take up nitrogen from the soil (or rather, the bacteria in the soil do). However, this is only temporary. When the work is done, the nitrogen is returned to the soil. But, more importantly, this process only occurs in the first centimeter (1/2 inch) of the soil. You can understand that the roots of plants go much deeper and that the lack of nitrogen on the surface does not affect them at all. Furthermore, decomposed ramial wood adds nutrients to the soil, including nitrogen, when the process is complete. It is not a thief, it is more of a borrower of nitrogen!

Mycelium in ramial chipped wood. Photo: permaculturenews.org

Fungi, however, because of their love of wood, will be more present under a ramial wood mulch. These fungi have a subterranean filamentous network, the hypha, that goes a few inches deeper than bacteria to get the nitrogen needed to decompose the wood. This could be a problem for freshly germinated seeds or young seedlings. For this reason, other, less woody types of mulch for a vegetable garden are often advocated, such as shredded leaves. But did you know that compost can also be used as a mulch? Just spread 5 to 7 cm (2 to 3 inches) of it, without mixing it into the soil. You could also move your ramial chipped wood mulch, which you will do anyway, when you plant. When your plants have grown, put the mulch back in place.

Just Mulch!

The moral of the story, don’t listen to everything you’re told, no matter how logical it may seem. Do your own research and use reliable sources. But most importantly, whether it’s ramial wood or not, use organic mulch! Your soil and plants will thank you.

Mathieu manages the jardinierparesseux.com and laidbackgardener.blog websites. He is also a garden designer for a landscaping company in Montreal, Canada. Although he loves contributing to the blog, he prefers fishing.

2 comments on “Is Ramial Chipped Wood Mulch a Nitrogen Thief?

  1. This is educational, but any soil scientist or horticulturalist with any soils training would explain the process you describe as temporary immobilization of the nitrogen. They would go on to say that the critical factor in determining the speed and extent of the process, besides temperature and moisture conditions, is the Carbon:Nitrogen ratio of the applied organic material. High carbon sources, like branches and straw will have high C:N ratios (up to 60:1.) Soil organic matter is closer to 15:1 (plus or minus). Nitrogen will be utilized until the carbon source in depleted to the 15:1 condition, and then the microbial population will die off and the N released.

    • Mary L Discuillo

      Can you repeat that in English? How bout the ‘gardening with mulch for dummies” version?

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