June 25, 2015

Mulch

Copyright Bob Osborne

I do not garden without mulches.  A clean cultivated garden is an unnatural and often hostile environment for a plant. In hot, dry weather it becomes a desert; the surface absorbs and gives off immense quantities of heat and lose moisture rapidly. 

Rains can cause erosion, and the surface layer can become packed from the impact of raindrops. After a rain the sun can bake the muddy soil into a hard shell, reducing oxygen levels in the root zone and leading to even worse erosion problems in the next rainfall.

Most plants prefer a ‘forest floor’ type of environment.  In a healthy forest, the mulch layer is an equalizer.  A mulch on your garden acts in the same way.  Its insulating qualities temper the heat of summer and the cold of winter. 

Mulch absorbs and disperses the impact of falling raindrops, eliminating erosion and preventing soil bacteria and fungi from splashing up onto plants where they can sometimes cause problems. The continual activity by worms, insects and other life encouraged by mulch also creates a network of pathways, which increases the availability of oxygen to the roots. 

Perhaps most importantly, an organic mulch provides a flourishing environment for the numerous insects and microscopic plants and animals that are necessary to a healthy soil.  Organic matter is continually broken down in such an active community.  This breakdown of organic matter releases nutrients into the soil where it can be used by plant roots.

 Whenever you add a large amount of organic material to the soil, it is important to realize that the breakdown of that mulch will require nitrogen.  Nitrogen fertilizers will provide this, although at the expense of some of the soil’s microscopic life, however, if a good quantity of well-made compost is incorporated on the surface just before adding your much, it will provide enough nitrogen and will further improve your soil’s texture and fertility.  If the mulch layer is not worked into the soil, simply add new mulch on the surface every year or two and the system will not overtax nitrogen supplies.  This gradual layering mimics the annual addition of leaves to the forest floor.

Inorganic mulches such as solid plastic sheeting exclude oxygen from the soil and should not be used, unless your object is to kill existing vegetation.  Landscape fabrics do allow for the passage of water and air and will keep weed growth down, but I have two major objections to them.  They are a nightmare if you want to work your soil, and pulling them up after a few years in the ground can be a job to tax the patience of any gardener.  Weeds that come in as seeds and germinate will work their roots into the fabric and make removing them extremely difficult.  Worst of all, these products are created from nonrenewable oil products.  It is bad enough that we squander these precious resources on things we consider essential, but to cover our gardens with them is completely unnecessary.

The most objectionable mulch I have found is shredded tires.  While such a product might be useful in certain situations such as a playground, where it can be contained and where it can be a forgiving and spongy surface, to use this as a mulch in a garden will inevitably lead to its incorporation into the soil.  This is like adding garbage to the soil. 

A mulch that I have found very valuable, particularly where perennials weed roots are still present, is cardboard.  Use cardboard that is not coated with waxes or plastics and remove any staples or tape.  Place the cardboard around your plants, setting them as close to the trunks as possibly.  Overlap the pieces of cardboard so it forms a complete seal.  To settle it in, wet the cardboard then place a mulch such as aged bark on top.

You can also use several layers of newspaper instead of cardboard.  This way you reuse an organic product and prevent weeds from working their way to the light.  Within a month or so you will barely be able to find the cardboard and it will be digested and returned to the soil.

One last note is to warn against using a deep layer of bark against tree trunks.  The trunks of both deciduous and coniferous trees will often rot if they are kept continually damp.  Use mulch around the trees but keep it away from the trunk itself.  Your tree will thank you.

Mulches are a wonderful way to keep your garden healthy and to save labour weeding.  Used correctly they will provide the same advantages as the annual rain of leaves on the forest floor.