Mulch 101

Applying wood chips as mulch in a garden bed.

What is mulching, other than a slightly odd-sounding word? To me, mulch has organic connotations and implies a breaking down of matter. This really isn't the case, however, as mulching can be both organic and inorganic.

The Benefits of Mulch for Your Garden

When the ground is wet, we can put something on top of it to prevent the moisture from evaporating and drying out the soil. If we do the same in the height of summer, then the water has an extra barrier to penetrate before reaching the soil and the roots of the plants. The best times to apply mulch are in late spring and autumn when the soil is warm and moist.

Other benefits of mulch besides moisture retention are that it can provide nutrients to the soil as it breaks down (if it's an organic material), weed prevention, and visual appeal.

Organic Mulch

Straw being applied to a flower bed as organic mulch.

Organic mulch options include bark and shredded plant material such as straw, mushroom compost, and seaweed. These options can all look attractive, give great contrast with the planted flowers, and provide good definition between the bed and the rest of the yard. As mentioned above, other benefits are that as organic mulch breaks down over time, it improves the nutrients in the soil.

Additionally, it keeps the moisture in the soil (as the underlying soil is protected from the potentially harsh rays of the sun). The downside of the organic mulch is that as it breaks down into the soil, it will need replacing periodically. It’s based on plant material after all, and in the same way that compost is broken down plant material, organic mulch will do the same.

The most popular mulch is wood chippings, laid to a depth of a couple of inches. This is a readily available option that can be bought from your local garden center. When I've installed mulch, I've used a fabric weed suppressant on the soil and then put bark chippings on top of it.

The fabric stops the weeds from growing and the bark covers up the fabric, which doesn't look particularly attractive on its own. In reality, I could have just used bark, but I really don't want to have to do any weeding. If new plants need to be added, then the bark can be brushed aside and the suppressant cut to allow access to the soil.

Inorganic Mulch

Small rocks surrounding a pine tree.

I moved into my house 12 months ago and when I first had a look around the garden, I noticed that a lot of the areas where I would be planting flowers were covered in old, black plastic. My first thought was that I had to clear it all up and it was another job to add to the list. What I didn't realize at the time was that this is actually a type of mulch. I just considered it a cheap alternative to the fabric weed suppressant that I was familiar with, but further research proves that it's a viable alternative.

The problem with plastic is that is doesn't biodegrade but instead goes brittle, falls apart, and is blown around the garden. What it is good for, though, is preventing the sun from getting to the soil. It's a very good weed suppressant because it prevents the process of photosynthesis and the growth of weeds. While this is useful in some aspects of the garden, it doesn't look great and won't let the water through.

While plastic sheeting doesn't look great, this isn't true for all inorganic mulch options. You can also utilize broken-up slate or stone chippings, which will be more expensive and labor-intensive to install than other options, but will last a lot longer and will not degrade due to exposure other than the sun bleaching the material.