Earthy Diversity: Mulch Types and Tips Part 2

In Part 1 we discussed carbon based types of mulch: wood chips, paper, cardboard, and leaves. In Part 2, we are going to cover green mulches.

But first, a recap on why mulch is so wonderful for your garden.

Mulch is fantastic for your garden for so many reasons. It helps with weed suppression, regulating the temperature of your soil, increasing water retention, and eventually breaks down and increases the organic material (OM) content of your soil.

All of these benefits improve overall soil quality which leads to healthier, happier plants. For every pound of material you harvest from a bed, you need to replace that in organic material to help prevent depleting the soil of nutrients and minerals. Mulch is a great way to do that.

So, what is green mulch? In a nutshell, green mulch is, well, green. It can take the shape of a living mulch such as an underplanted cover crop, or plant material that has been cut down and left on the soil surface without going through any sort of drying process first. 

Living mulch

This walkway in the author's production field has a mixture of wild violets, grasses, and clover. 

Live plants as your green-mulch layer work to outcompete any weeds. If you choose a flowering type, there is improved pollination for your crops, and there is increased photosynthesis occurring which helps feed the soil organisms,  improving soil health and therefore plant health. You also don’t need to worry about nitrogen lockup or annual reapplications as you do with carbon-based mulches.

Things to keep in mind when utilizing living mulch are location, how vigorously the plants spread, and how tall they get.

If you are wanting to utilize living mulch for a pathway, then you’ll need to use plants that can be walked on with little issue. You also need to be honest with yourself in determining how often you are realistically going to be outside maintaining the pathway.

If you enjoy revving up the weed whacker, then you have a bit more flexibility in what you can use as a living mulch. If you want to plant it and forget it then you should really focus on selecting plants that stay very short, like creeping thyme, or skip this method altogether. 

In my flower production field, I mulched my pathways and seeded New Zealand White Clover to act as my living mulch. It took well in some areas, and not as well in others, so now I have a mixture of clover and perennial grasses in my pathways.

I am someone who absolutely loves yard work, so I am gleefully running the weed whacker every other week in the shoulder seasons, and weekly when everything grows way too fast. This way I can keep the clover and grasses from growing into my beds as well as prevent them from setting seed in the beds.

I really enjoy having living pathways because I don’t have to keep spreading mulch every year. I’ve found the more soggy parts of my field that have mulched pathways stay soggy for longer after big rain events, unlike the living-mulch pathways that dry up much faster. Pretty cool, right?!

Other things to be aware of is that you can’t direct seed into an area that has an established living mulch. The existing plants will compete and shade out any seedlings.

The author's ill-fated zinnia seedlings that were planted into too thick a layer of green material in direct contact with said material. 

The best way to use living mulch in your beds is to seed the mulch layer either at the same time, or just a smidge after planting your primary plants. You don’t want to wait too long since the understory needs time to get established before being shaded out by the primary plants.

Another consideration is making sure your plants still have good airflow, especially if you live in a humid environment. With dense, tall plantings you risk fungal issues. Keep the understory on the shorter side to help prevent that from happening. 

Chop ‘n drop

One of the author's container fruit trees with a creeping thyme living mulch eventually grew to cover the entire surface.) The fava bean plants were utilized for the chop and drop method there in the container once they grew to maturity.

The chop and drop method of mulching is where you cut green plant material and lay it down on the ground as a mulch.

Depending on how thick the layer of green material is, and if the pieces are whole or cut up, will impact the amount of time needed for the decomposition process. The smaller the pieces, the faster they will break down. 

Some plants are well known for their nutrient-mining capabilities meaning they are really good at collecting trace minerals from the subsoil that many annual plants are too shallow rooted to collect.

Not only do these plants collect a lot of trace minerals and micronutrients, they also produce a TON of foliage which makes them great for using as mulch plants.

These plants include comfrey (make sure to get a non-spreading variety), yarrow, and nettles among others. Borage and fava beans are annuals that make for great chop and drop plants too since they produce an incredible amount of biomass. 

Without getting too into the weeds here (Get it? Weeds in a mulch article? I’ll see myself out...) using annuals for growing out a lot of biomass, then cutting them down and planting into it as a biodegradable mulch layer is exactly what cover cropping is all about.

The important note with this is: When you have a lot of green material on the soil surface decomposing, the decomposition process can get really hot which can be bad for plants, and all the microorganisms involved in that decomposition process can get a bit carried away and go for your plants if they are in direct contact with the decaying plant material. 

This isn’t a problem if there isn’t a lot of green material, nor is it a problem if you make sure there is space between the material and your seedling; about a 2-inch ring should do the trick.

Don’t be like me and put down 3 inches of chopped-up radish cover crop and nestle seedlings right into it without providing breathing room. About half of the seedlings rotted before I figured out what was happening.

I put down a light layer of wood chips to balance out the nitrogen levels and gave the seedlings space away from the decomposing material with wood chips covering that open space, and they grew up into beautiful plants.

You could also allow the green mulch to decompose for a while before planting into it. Experiment and see what works for you! Each planting timeline and scenario is different and will require different techniques. 

Final thoughts

Using living mulch in pathways and in perennial beds is great for keeping the soil covered, microorganisms fed, water retained, and all of the mulch benefits without having to apply a new layer every year. The downside is having to do some level of maintenance whether it’s edging or trimming it down. 

Chop and drop mulching is great for established plants, containers, and raised beds. Just be mindful of how thick of a layer you are putting down and that it doesn’t come into direct contact with the target plant. 

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