Mulch Musings

Mulch is a great way to show love for your baby trees!  It will suppress weeds, increase water retention and can help beneficial mycorrhizal fungi, saving you time and improving the health and growth of your nut seedlings.  There are many different materials that can be used for mulch from organic materials to plastic ground cover to gravel and they all have different benefits and potential problems.  What you choose will depend on your planting site, your goals and your values.  We want our Mulch Musings to be a resource to help you choose the best mulch for your situation.  If you want to jump ahead and just read about our recommended mulching regime click here.

Benefits and Risks

The benefits and risks from mulching are complicated and site specific, but generally we can compare mulching with the two alternatives: using physical or chemical weed control (ie. hand/machine weeding or herbicides), or just leaving your trees to fend for themselves.  While the trees will do fine without mulching or weeding later in life, they will be much happier with some extra attention when they are getting established. There are, of course, differences between various mulch options and we will go into more detail on that below.  

Weed Suppression

A good mulch will suppress weeds enough to allow your trees to get more nutrients.  While most mulches will not eliminate weeding completely they will save you time by allowing you to weed less often and will make pulling out weeds easier and less disturbing to the trees.

Water Retention

Mulch creates a layer that reduces evaporation from soil thereby improving irrigation efficiency.  Maintaining a moist area around the base of young trees also allows strong root system establishment and a more consistent supply of water.

Mycorrhizal Support

Mulching with organic matter helps create an environment where mycorrhizae can thrive by keeping the ground dark and moist with a constant supply of food for the fungus to break down.  Wood chips are particularly good at feeding fungus that will in turn feed your trees, see below for more details.

Rodent Damage

Rodents can be encouraged by certain types of mulch. Voles, or field mice, are the biggest concern as their near surface tunnelling is much easier with fluffy mulch material lying on the surface and they like to eat the roots and the bark of young trees, potentially decimating newly planted seedlings. Loose mulch materials such as straw, or long untrimmed grass should generally be avoided around the base of trees so that rodents don’t have easy passage to the trunks.    Plastic mulch and hemp mulch mats can also make ideal habitat for rodents to move freely underneath and should be monitored for rodent tunnelling activity.  Heavy mulches like wood chips and gravel are generally much better at deterring rodents as they force them to either go below ground or on top of the mulch before they get to the base of the tree.  When selecting a mulch the rodent pressure should be taken into account; are there signs of rodents? Is there good protected habitat nearby (ie. long grass)? Are there predators that will control the population (cats, snakes, owls, hawks)?  An inner mulch layer of pea gravel is a great way to protect the base of the trunk from foraging rodents.  See below for more information on how best to mulch so that rodents are not an issue.

Rot

While young trees will benefit from decomposing organic matter on the ground around them, they certainly do not want organic material touching their trunks!  Non-organic mulches like pea gravel are a great way to mulch the base of a tree without worrying about rot, as they allow for water to drain but maintain a ground cover that keeps weeds back.

	Leave trees to fend for themselves	Physical/chemical weed control	Plastic Mulch	Organic Matter Mulch
Weed Suppression	bad	very good	very good	good
Water Retention	okay	bad	good	very good
Mycorrhizal Support	okay	bad	okay	very good
Rodent Risk	high	low	high	depends on material
Rot Risk	low	very low	low	medium

Mulch Options

There are many different ways to mulch trees and what you choose will depend on your site, budget, time, materials available and values.  Don’t be afraid to be creative with mulch materials, but think about the properties of what you are going to use and what benefits and risks it will create.  

Our Recommended Mulch Regime (Wood Chips and Pea Gravel)

In general, we think the optimal mulch for most nut trees is a thick layer of wood chips with an inner ring of pea gravel directly around the trunk of the tree.  Ideally, hardwood chips from small diameter trees and branches are used as they contain the best ratio of nutrients for nut tree growth and mycorrhizal success.  These are referred to as ramial wood chips, you can read more about them here.  An alternative to ramial wood chips is uncomposted hardwood bark from a sawmill, as this contains the bark and cambium layer of the trees.  Often, at least in coastal BC, it is much easier to find (or make your own) softwood chips and while these aren’t as ideal they still provide a good mulch that breaks down over time to feed mycorrhizae and your trees while suppressing weeds.  

 

We often lay a layer of cardboard or kraft building paper down around the tree before mulching to provide an extra decomposing layer to suppress weeds.  With a 4-8” layer of woodchips it will stay in place and will be held close enough to the ground to prevent rodent activity.  Keep the paper/cardboard and the woodchip layer 6” away from trunk.  The hole in the middle can be kept open or, ideally filled with pea gravel (larger gravel works too).  This allows you to mulch right to the trunk without risk of rot and will help protect your trees from rodents.  

We have found that mulching like this lasts for years with minimal weeding required.  If you are able to, it is beneficial to start with a thicker layer of mulch (up to 12”) and to add mulch over time to maintain the mulch doughnut.

Hemp Mulch Mats

As you may have noticed, we sell hemp mulch mats on our website.  You may wonder why we sell a product that isn’t our recommended mulch material.  The answer, of course, is that you can install a mulch mat in 30 seconds, while mulching with wood chips and pea gravel as we recommend takes a lot longer, requires a lot more organizing and usually costs more as well.  So while we love the thought of everyone mulching with wood chips, we want to offer something quick and simple that will actually happen!  

 

To be honest, we are still trialing the hemp mulch mats, so we can’t say for sure how long they last, how good they keep the weeds down and if they will cause issues with rodents.  That said, we can say that they are very quick to install and definitely do suppress weeds, although you will likely need to monitor them for movement in the weather and do some weeding a few times a year to make sure they don’t get overrun.  The fact that they are biodegradable means they won’t last forever, but also won’t leave behind a bunch of microplastic in the soil, making them an environmentally friendly choice as well. 

Plastic Mulch (ie. Landscape Fabric)

Plastic mulch is by far the best mulch for long-term weed suppression but it comes with a number of caveats.  There are different options for plastic mulch, but most orchards that use plastic will use a woven landscape fabric that lets water through but stops most plants from growing.  Unfortunately, some pesky weeds, like Kooch Grass, may get through, and there will always be a slow creep of plants growing on top from the edges.  The big risk with plastic mulch is rodents having a field day underneath where they are protected from predators and can nibble away at the roots of your trees.  One way to mitigate this is to cut a hole in the plastic around your trees’ trunks so at least the trunk has a little distance from rodent heaven.  However, the bigger the hole, the more weeding you will have to do anyways, so it is a bit of hard one to get just right.  

Other considerations are cost and installation time, both of which are substantial, and the long-term microplastics that will be left behind as the plastic breaks down (which it will, especially as roots from grasses and weeds grow into it).  There are biodegradable plant-based plastic mulch options which may last long enough to help new nut seedlings get established, however, if you are putting in the money and the effort you may be better off with wood chips.  

We have seen examples of plastic mulch working well in orchards but it must be managed thoroughly.  Ongoing maintenance of the plastic’s edges and holes around the trees, as well as regular mowing of the alleys in between will help keep the rodents and weeds from taking over.  As you may have noticed, it is not our first choice, mostly because we are aiming to build a holistic system in our orchard where mulch is a part of supporting and feeding mycorrhizae and trees, but for some people plastic mulch is the best choice for reducing weeding in the long run.

Straw and Hay

Straw and hay are often used as mulch in gardens but we don’t recommend them for nut trees.  The biggest concern is that they make good rodent habitat, and that may lead to serious tree damage.  If you have a bunch around that you really want to use in the orchard make sure you give the tree trunks a wide birth.

Thanks for reading our Mulch Musings.  We hope it has been helpful!