by putting wood shavings on a vegetable garden does it harm it or help it, I was told 2 different things…I was told it takes all the nutrients out of the garden, and I was told if I fertilize it doesn’t matter…please help


Thank you for contacting Toronto Master Gardeners.

You are correct that there is a lot of conflicting information going around about mulch, much of it not science based. There has been a lot of research done in recent years that shows many of the old theories do not make sense.

Theories about mulch taking nutrients out of your soil or changing the pH of your soil have no grounding in science. Studies have been done and they are just not finding it to hold true. If anything, it increase the nutrients in the soil.

Mulch has many benefits for your garden.

  • A layer of mulch will help retain moisture, decreasing the amount of watering needed. It also will stop the surface of the soil from becoming hard and impenetrable from rain.
  •  The mulch will help smother weeds by depriving them of light so there is less weeding for you to do.
  • The environment under the mulch will draw microbes and insects to the area. This will start to loosen up the soil and create aggregates which are essential for water retention and enable the plants to pull nutrients from the soil more efficiently. Minimizing digging will help your soil retain these aggregates. After a few years you will have much healthier soil in your garden.
  • As the environment under the mulch becomes rich with microbes, fungi and insects the soil will loosen up and allow the roots of the plants to have better access to oxygen which is critical for plant health.
  • The mulch can be left on the surface and new mulch added on top when the original mulch starts breaking down. As it breaks down it will release new nutrients into the soil.

There are many types of mulch. The most effective is wood chips. Depending on the size of your gardens there are several ways to get wood chips.

  • Arborists will often deliver them free as they have a huge supply and have to pay to dispose of them. They would rather people use them as it saves them money. This would be a large amount so you need a large garden to take advantage of this.
  • There are many companies that will deliver a large bag to your house, usually to the end of your driveway. The bags look large but once you start laying several inches on the garden it gets used up fairly quickly.
  • At nurseries you will find many types of mulch in smaller bags. Many of these mulches are made from bark which is water resistant. Bark will not have the same water retention benefits as wood chips and not create as healthy an ecosystem  in your soil.
  • You will also see dyed mulch. Wood chips do not absorb dye readily so these mulches are made from reclaimed wood scraps and wood pellets and bark. The dyes do not seem to not be an issue but the chemicals that the reclaimed wood may have is. There is a risk of creosote and other chemicals getting into your garden.

You mention fertilizing the gardens. Before doing that it is highly recommended that you have your soil tested. Most garden soil actually has the nutrients you need and fertilizing can lead to excess amounts of various nutrients. This can be just as damaging as not enough nutrients and is not fixable except with time. You can always add but you can not take them away. Many of the self testing kits you can buy in nurseries will not give you a full picture of what is in your soil.  The procedure is fairly straight forward. they can also test for contaminants if you have any concerns.

I have attached a links for further reading on mulch, dyed mulch and Ontario soil testing labs.

Soil Testing in Ontario:

Myths about Mulch

Colored Mulches