Deliciously red colors of redwood bark mulch

Mad About Mulch
The Northern Gardener's Secret Weapon Revealed
by Jim Kohut, Staff Writer

You’ve probably heard enough people talk about mulch, but do you really know what it is and why it is so important in our northern yards and gardens? If there’s only one thing that you as a northern homeowner take away from Northscaping this year, I want it to be the concept of mulching. I am convinced that no other single intervention can have a greater impact on the success of plants and the maintenance requirements of a home landscape, not to mention an enormous visual impact on the overall composition.

Mulch is somewhat of a “catch-all” term, but it effectively describes any material, be it organic or artificial, that is placed on top of the soil over the root zone and/or crown of a plant, or for that matter that covers the exposed soil of just about any part of a garden or landscape. Nature itself is big into mulching; just observe a native forest floor in fall or early spring, covered in fallen leaves and other organic debris.

	Even nature is into mulching!

But most often, and for our purposes, mulch is an element that is intentionally introduced by humans into our yards and gardens with specific intent. We do this for three primary reasons; for the benefit of our plants, to reduce maintenance, and to cover large parts of our landscapes in designed and selected materials. Regardless of the intent, an effective mulch needs to be both functional and ornamental, and that’s why we need to examine both the intended purpose of the mulch, and the aspects that make a good mulch work in a landscape composition.

Let’s start by looking at the various ways that mulches are used in our landscapes.

Mulching For The Benefit Of Our Plants

Mulches are most commonly used to protect the plants in our yards and gardens, and to give them a leg up on the inevitable competition from weeds and the lawn. They also reduce maintenance for us humans, and they can make the difference in winter survival.

There are essentially two kinds of mulches in terms of plants; summer mulches and winter mulches, and they have very different purposes. Summer mulches are applied around the bases of plants and across the surfaces of gardens to preserve moisture and to inhibit the growth and spread of weeds. They help retain moisture by shielding the soil from drying winds and the direct heat of the sun, and can go a long way to reducing your watering bill each summer. They also limit compaction of the soil, and they virtually eliminate the need to regularly till the garden soil.

The benefits in terms of weed control are by far the most important, though, both to the plants themselves and to their human caretakers. A thick layer of mulch makes it difficult for weed seeds to germinate and establish themselves, and even if they do manage to get established, the mulch prevents them from getting a good footing in the soil, making them quite easy to remove by hand. This weed-free border around plants and in gardens virtually eliminates competition for our favored introductions, affording them the best chance for survival and motivating their best possible performances when they are called to take the stage.

In this sense mulches help contribute to a low-maintenance landscape, but don’t be fooled into thinking that they make a landscape zero-maintenance. I like to refer to this as the “zero-maintenance myth”, and that’s what it is, a myth. If anyone promises you a maintenance-free landscape, they’re either selling you a service or selling you snake oil. But mulches will definitely reduce your workload, I can assure you of that.

Newly planted trees benefit from a mulch perimeter

Summer mulches also offer a critical protection zone around the perimeter of plants and gardens. Most people don’t realize that the #1 killer of plants in the home landscape, especially trees, isn’t winter, but rather mechanical damage from lawn mowers, weed trimmers and other maintenance equipment. As grass grows up to the base of a tree or shrub, so our lawn care equipment gets ever closer, and it inevitably reaches the point where we start to inadvertently hit the trunks and stems with our equipment. The soft bark of plants, especially young ones, was never meant to be hit by mechanical equipment, and the resultant wounds allow for entry by disease-causing organisms and insects, and void any protection from the extreme cold of winter that bark offers. Having a safe-zone around our plants keeps the equipment at bay, and the plants happy and healthy as they mature.

Organic mulches offer a further benefit that warrants mentioning. Over the course of a few years, organic mulches decompose and work themselves into the soil as organic material. This process mimics that which actually occurs in nature as fallen leaves and dead branches and trunks are recycled into the soil. The result is highly beneficial to the soil, keeping it rich and pliable. Obviously, this requires that organic mulches be replenished every few years as they return themselves to the soil, but the benefits to your plants are well worth the extra effort.

In fact, mulches can actually be used to amend the growing conditions for specific plants. Pine needles decompose into a highly acidic organic material that Ericaceous plants like rhododendrons, blueberries and heather just adore. At the other end of the spectrum, if your soil is too acidic and sour, a mulch of crushed limestone will leach alkaline elements into the soil and sweeten it just enough for some of the fussier plants to be happy.

Winter Mulches For Survival

At the other end of the scale is winter mulching. The crowns (the parts where the stems and trunks meet the roots) and the roots of plants tend to be the least hardy parts and the most subject to winter injury, especially when exposed to the extremes of winter. Remember that in nature, the root zones of plants are covered in a thick mulch of fallen leaves and other organic debris as well as a thick layer of snow during the coldest months of winter, but this is often not the case in our modern landscapes.

	Straw can help carry tender plants through a harsh northern winter

Mulch acts much like the insulation in your home, effectively trapping a layer of air inside and protecting the root zone from extreme swings in temperature. In this way, the latent heat of the summer which has built up in the soil is preserved into winter, allowing the roots to grow for a longer time even after the snows have fallen. And likewise, it delays the warming of the soil in spring, holding off the budding and growth of the plants a little longer and dodging the damages of a late spring frost.

For all trees and most of the larger shrubs, the objective of a winter mulch is to provide insulation to the root zones. In the case of smaller shrubs, and tender shrubs and perennials, the mulch is intended to cover both the roots and the crowns, and at times even parts of the lower stems which may be required for flowering the next season, as is the case with tender hydrangeas or hybrid tea roses. In these cases, the mulch may be mounded high over the plant, and removed with the arrival of spring.

Mulch As A Groundcover

One of the most effective uses of mulch is as a non-living low maintenance groundcover. Groundcovers are surfacing materials we introduce into our landscapes to cover large areas of land to limit maintenance, increase functionality and maintain harmony with the overall composition. You’ll be familiar with plant-based groundcovers such as lawn grass, large plantings of perennials such as Japanese spurge, and shrubs like junipers and cotoneasters.

Many times, though, a design requires a permanent and durable solution to covering a large space. While certain plants require much less attention than others, plants in general are anything but low-maintenance. This is where mulches can play a significant role. Because they are inherently lower maintenance than plants, and can be selected according to their design attributes, they are ideal for this application.

Mulches are often used to cover large garden expanses in professional gardens and arboreta, and this is a practice that carries well into home landscapes. These mulches can dramatically reduce weeding and maintenance in between plants where you really don’t want things to spring up, and can contribute ornamentally to the garden composition itself, providing a solid backdrop of color and texture against which the plants can do their thing.

Designing With Mulch

The good news is that there are all kinds of materials that make effective mulches. The bad news is that because of this, you really should put some effort into selecting the right mulch at the start of the process, rather than trying to correct a bad decision later on.

The first thing to consider about a mulch is its specific function in your landscape. If you’re using it to insulate the root zone of a plant, then it should have a high insulation value. If it’s intended to keep maintenance to a minimum in a garden or a large tract of land space, it should be inherently low maintenance.  If its primary function is ornamental, then it should be selected for its ornamental qualities.

River wash stone has a distinctive look

Like all the elements that comprise your overall landscape composition, mulches should be considered in terms of their basic design attributes; color, texture and form. Color is by far the most important, as mulches typically cover large areas or are visually prominent at the bases of trees. As a designer, you’ll be pleased to know that mulches come in a wide range of colors, most of them related to earthy tones and the colors of nature, which blend particularly well with plants.

One important consideration with color is the effect of the sun. Dark mulches will retain and accumulate heat in the sun, while light-colored mulches will reflect the sunlight and keep the root zone cool. Be careful about dark artificial mulches; on a hot summer day, they can absorb so much heat that they can actually bake the roots underneath, thereby killing the plant!

Mulches should also be in harmony with the overall composition. So if your style or theme is natural and flowing with lots of wood elements and structures, you would want to use natural and organic mulches. If on the other hand you have a contemporary or art nouveau style, then more artificial mulches would look in place.

Texture is another critical consideration. From a distance, mulches should be highly uniform, not jumping out but rather blending in as a background against which the feature elements in the landscape are highlighted. Up close, however, they can take on a character of their own as the textures become evident. Smooth and rounded stones, large chunks of redwood bark, sharply cut shale fragments, fine pine needles; each of these present the up-close viewer with a different type of interest derived through these forms and textures.

Then there are the practical considerations such as maintenance. Organic mulches will need replenishing every few years as they decompose and integrate with the soil. There is also the aspect of performance and durability. If the mulch will be occasionally trampled on, then it needs to be able to withstand that kind of traffic without breaking down.

In terms of applying mulch, the process is actually quite straightforward. First prepare the area to be covered by killing and removing all weeds and leveling the soil surface as much as possible. Then apply a thick and even layer of the mulching material, right up to the bases of the trees and shrubs, but don’t pile them high onto the trunks - keep everything level. Be sure to leave a small margin around perennials to allow them to come up and spread a little.

	A thick layer of mulch will keep your shrubs healthy and maintenance-free

As for thickness, generally speaking thicker is better, but also costlier. If you can afford to apply a uniform mulch of 3-5” thick, do so. If not, as in the case of very expensive decorative stone or colored bark chips, you may want to “cheat” by first applying a sub-layer of a cheaper material, and topping it off with an even 1-2” layer of the more expensive stuff. Trust me, this trick works!

The big question with mulch is always whether or not to use landscape fabric underneath. Unfortunately, there is no single right answer. Landscape fabric will further inhibit germination of weeds, but won’t eliminate it. It will also block the returning of favorable organic materials into the soil. My personal advice is as follows; when using a rock or stone mulch, always put landscape fabric underneath. For decorative mulches, the choice is yours. If, however, you want the advantages of organic mulches in your soil, then do not use it, with the knowledge that you will have to replenish the organic mulch a little more frequently.

All Types Of Mulch Under The Rainbow

Here are just a few suggestions for mulching materials.

Functional mulches;

Shredded tree and shrub materials - commonly available at the local dump or municipal yard, extremely cheap (sometimes free!), highly effective as organic material but needs frequent replenishing, can be overly dirty (e.g. weed seeds, insects, disease)

Wood chips - very functional and effective, a great organic choice that lasts longer than shredded plant materials, tends to fade over time and does need replenishing every few years

Shredded bark compost - one of my personal favorites but hard to come by, this is pre-composted plant material that is well on its way to becoming a fine soil amendment, has a relatively short lifespan but does wonders for the soil

Pine needle mulch can help acidify alkaline soils

Straw - the ultimate temporary winter mulch for tender perennials and lower shrubs

Pine needles - if you need to acidify your soil or want to grow azaleas and rhododendrons, then seek this out even if it means driving a hundred miles!

Decorative mulches:

Colored or textured bark - costs a fortune per square foot of coverage, but nothing looks finer, available in an amazing array of designer textures and colors, does need replenishing though

Colored stone - ideal for low maintenance but not cheap, best used for more modern and stylistic landscapes, keep a consistency in shape, size and color of the individual pieces

River wash stone - smooth rounded stones for a wonderful effect, quite expensive though

Other mulch ideas:

Pre-manufactured mulch rings - effective for newly planted trees, but why pay a premium for the same benefit?

Newspaper - I’ve heard of this, and why not, but then again, how can you make newspaper “work” in a balanced landscape composition?

Common Mulch Problems

There are a few substances that should be avoided in a mulch mixture. Stay away from anything with chemicals, for example treated or painted wood, as the chemicals can leach into the soil and create a toxic mess. Know the source of the organic materials in your mulch. It is far too easy to transmit insects and diseases that killed the plants that are now shredded in your mulch into your own landscape. Never use dead or decaying fruits in a mulch as they can host a number of insects that will gladly move on to your prized ornamentals.

	Don't fear the mushrooms...

Mulch can and often does contain foreign plant materials and seeds, particularly weeds. Use the cheaper municipal shredded tree and shrub mulches with the knowledge that you will be plucking out introduced weeds and “volunteer” plants from your gardens and tree rings for the first year, although they will settle down after that. Most of the higher quality commercial mulches will have been cleaned before being put on the market.

Some people are concerned with the appearance of mushrooms in organic mulches. There’s no worry here, as they are a natural part of the decomposition process. If you are concerned about children or pets consuming these potentially toxic fungi, however, you may want to avoid organic mulches.

While they protect your plants, many winter mulches like straw can also host mice and voles over the winter, who can do far more extensive damage to these plants than the winter ever could. Around here, the “common wisdom” is that these vermin dislike flax straw and won’t set up shop in a flax straw mulch, thus it is said to be a preferred choice for mulching. I can’t independently verify this, but who am I to argue with local lore?

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