What Kind of Mulch Should I Use?

Think of mulch as insulation for your garden plants and their roots.

Why Mulch?

Mulching is incredibly important for many reasons. It keeps root zones moist and at even temperatures, it helps suppress weeds, and is part of a healthy soil system because it adds organic matter as it breaks down. That last point is important because the beneficial micro-organisms in the soil feed on organic matter. They further break it down (compost it) which makes the nutrients in the mulch available to plants. Also, that organic matter is bulky and creates air and water channels. There is no question we should be mulching. The only question is what to mulch with and that is what we are going to discuss here.

What Not to Use as Mulch

Let’s start with what not to use. Artificial mulches made with plastic or rubber should not be used. They don’t break down and add organic material to the soil. By using these we are removing one of the vital reasons for mulching which is feeding the soil.

Can I Use Dyed Mulches?

It’s best to avoid dyed mulch. Unlike natural mulches that come from trees and yard waste, dyed mulches generally come from old wood like pallets, decking and sometimes pressure treated lumber which was likely treated with CCA which stands for Chromium, Copper and Arsenic. Dyed mulches do not break down effectively and could possibly leach harmful chemicals into the soil.

What About Stone for Garden Mulch?

Some gardeners in more arid climates use stone as a mulch. In that kind of soil and with those kinds of desert like plants it will work as their climate is naturally arid. However, for a general garden it’s not advised to use stone for mulching except for something aesthetic like a dry stream bed.

Is Landscape Fabric a Good Idea?

Simply put landscape fabric under the mulch is not a good idea. This is the black cloth fabric you can put on top of the soil and then cover with mulch. It’s meant to assist in keeping weeds down. While it does work do that it’s best not to use it. Recall our third point about the importance of organic matter breaking down into the soil. Landscape fabric will prevent the broken-down material from getting into the soil where it is a vital part of soil fertility. While it will allow liquids to flow through, there is no liquid product that can replace the benefits of broken-down organic material. Plus, if you ever tried to add new plants to a garden with landscape fabric you know how difficult it can be to “dig” through it.

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What Type of Mulch Should I Use?

So, what should you use? We’ve established it needs to be a natural product and generally there are two choices. Hardwood mulch or pine straw. Let’s start with hardwood mulch.

Hardwood Mulches Work Great to Feed Soil

Hardwood mulches (also known as arborist chips) tick all the boxes when it comes to mulch. First, they break down and add nutrients to the soil. If sourced in bulk locally the mulch likely came from trees local to your area. This is helpful in that you are adding organic matter to your soil similar to what nature has been adding for thousands of years. Hardwood mulch also has “bulk” to it allowing good passage of water, air, and nutrients into, and through, the soil. Ask for “double ground” which means it’s been ground down twice.

How Do I Know If the Mulch is Breaking Down?

When adding mulch in spring, spread to the depth of about 3 inches. In the fall peel pack the top layer to see if the part in direct contact with the soil is decaying or composting. If you see white strands in there rejoice as that is known as mycelium. It’s a naturally occurring fungus whose job is to break down organic material, exactly what we want to happen in the garden and landscape. Mulch can break down quickly and in fact over the course of a season most of it should break down and become compost.

What If the Mulch Isn’t Breaking Down?

A little tip is that if you have not used mulch before or it is not breaking down then add a layer of compost on top of the soil and then mulch on top of that. The compost will help the mulch break down and start the process that will occur year after year on its own. Think of the forest floor. Organic material falls mostly in the autumn, is broken down with the help of what fell the previous autumn and has now become compost. The next year that happens again and so on. That is what you are trying to reproduce in your garden.

Does Pine Straw Work as Mulch?

Pine Straw (or pine needles) is commonly used where pine trees are readily available. It is an effective mulch in that it keeps soil moist and cool, suppresses weeds and will break down over time.

Will Pine Straw Make the Soil Acidic?

A common myth is that pine straw will make the soil acidic. This has been debunked by numerous scientific studies and is not a reason to not use pine straw.

What Are the Advantages of Pine Straw Mulch?

Advantages are that if you live in an area with lots of pine trees it’s readily available and generally cheap. On a slope they tend to be more stable than hardwood mulch as they are less likely to be washed away by rains.

Are There Disadvantages?

A couple of things to keep in mind about pine straw is that it can be flammable and sometimes small insects and rodents will burrow into it as shelter. Not a reason to avoid it but just be aware.

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Choose Your Garden Mulch

Ultimately, whether to use hardwood or pine straw mulch depends on what you can most easily and affordably get. Also, which looks best to your eye. I’ve always used double ground hardwood. I like the way it looks, and my plants have always liked it too. I also know a lot of gardeners who use pine straw and are also pleased with the results. Whatever your choice add mulch annually and your plants, and soil, will thank you for it.