Cover Crops: Living Mulch

One way to support good soil is to keep it covered using an organic mulch. We’re all familiar with mulches like straw or woodchip, but the benefit of growing a living mulch also needs to be considered.

One way to support good soil is to keep it covered using an organic mulch. We’re all familiar with mulches like straw or woodchip, but the benefit of growing a living mulch also needs to be considered.

Healthy gardens are built on healthy soil. Without it, it’s impossible to create the living and sustainable foundation an abundant garden needs. Mulching your garden provides plentiful benefits. Not only does it retain soil moisture and protect precious top soil, it helps minimise weeds and fosters an active soil ecosystem of microbes, fungi, bugs and earthworms to support thriving, happy plants.

In annual garden beds, it can be useful to have the flexibility to remove mulch at different times of the year, like in early winter or spring when you want sunlight to hit your soil and warm it up. In perennial beds or under fruit trees however, a more permanent mulch can be really useful. This is where planting a living mulch can be a clever solution.

Wasabi greens
Wasabi greens used as a biofumigant cover crop. Photo by Julie Bennett

Reasons Why

A living mulch is any low-growing plant that acts as a ground cover, protecting the soil in the same way any other mulch might. They are placed around and underneath other plants, often fruit trees, trellised plants or even upright-growing annuals like tomatoes. Living mulches act as helpful companions to the main crops around them by complementing their growing needs and protecting the soil.

There are plenty of great reasons to plant living mulches in your patch, not least because they shade the soil and retain moisture by reducing evaporation and insulating the soil temperature. They create a dense understory that can outcompete weeds and creeping grasses like Kikuyu or Couch grass and many living mulches are flowering plants which attract pollinators and beneficial insects, creating a pest-resilient garden.

Living mulches increase soil fertility and organic matter, particularly if they are nitrogen-fixing legumes that take nitrogen from the air and convert it into a plant-available substance in the soil. This benefits the whole soil ecosystem of microbes, fungi, earthworms and other bugs. They are a much better choice than non-living mulches when used on steep slopes or areas with heavy rain or high winds because they stay where you plant them, and of course, they reduce your work in the garden with less mulching and weeding required.

Choosing A Living Mulch

Choosing the right living mulch for your garden comes down to where you are planting it and what its purpose is. Much like companion planting, you need to make sure you are pairing plants that complement each other and that won’t be directly competing for essential sunlight, nutrients and moisture, or causing issues like restricting airflow in such a way that you end up with fungal diseases or pests.

Living mulches act as helpful companions to the main crops around them by complementing their growing needs and protecting the soil

Start by considering the root type and depth of the living mulch and the other plants you are matching. Do the plants have different root depths and types, or will they be competing with each other for nutrients and water? Planting a shallow-rooted ground cover like white clover underneath fruit trees that have a deeper and more extensive root system, for example, would work well. A simple option for reducing competition is to choose plants with different growing seasons, like a ground cover that thrives in winter beneath deciduous trees.

Living mulches are usually low-growing plants because they typically don’t interfere with the plant foliage above and leave adequate space for sunlight and airflow. Choose plants that give each other plenty of space for adequate sunlight and airflow by considering their height and how vigorously they grow. The last thing you want is to smother your plants with a rampant climber that creates more problems than solutions.

Some plants, like nasturtiums, produce a prolific amount of seed each year – if you plant them once, you’ll end up with them year after year. While self-seeding is handy, just be mindful of where you are planting these persistent growers. Another thing to be aware of is that using living mulches in cool or damp weather can provide a perfect slug and snail playground. Keep this in mind when deciding what to plant where or be prepared to protect any young or tasty annual crops you plant nearby.

Picking The Right Plant

There are many different plants to consider when choosing a living mulch. Mix and match, and don’t be afraid to plant a variety of complementary plants together.

Flowers

Flowering plants as living mulches are an obvious choice, as they have the added advantage of attracting beneficial bugs and pollinators to your garden, as well as looking beautiful. Consider nasturtium, calendula, marigold, sweet alyssum, phacelia, violet or seaside daisy – all provide good ground cover and flower prolifically.

mulch
Photo by Nola Ryan
mulch
Photo by Robyn Rosenfeldt
mulch
Photo by Robyn Rosenfeldt
mulch

Clockwise from top left Under fruit trees, living mulches can also attract pollinators; Taprooted plants like comfrey draw nutrients from the soil making them useful chop-and-drop mulches; Nasturtium (right) and white clover (left) are shallow-rooted and edible, though both are prolific and difficult to get rid of once planted.

Herbs

Herbs are another easy choice, especially in orchards or under trees. Their aromatic foliage and flowers both deter pests and attract predators and bees, with the added bonus of providing a tasty and useful harvest. You could use almost any herb, like thyme, oregano, low-growing rosemary and chamomile, chives, borage, sage, lemon balm (be mindful, it will spread) or yarrow. Although they are a short-lived perennial, strawberries also make an excellent edible living mulch.

Nitrogen Fixers

Including ground covers like white clover, red clover or vetch in your living mulch has the added benefit of boosting your soil nitrogen alongside being a highly effective mulch and bee-haven. If using white clover, choose its placement carefully as it’s a vigorous grower and self-seeder.

Comfrey is another powerful living mulch addition. It has a deep taproot and an extensive root system that very effectively draws in the nitrogen and minerals in areas where it may be leaching away in damp soil or where there are high concentrations – like around chicken coops – and stores it in the leaves. These can be cut and placed on the ground as mulch, used to boost compost or make weed tea (Pip, Issue 22). Bees love the flowers, it forms a dense cover in warm weather that effectively chokes out weeds and it also has medicinal benefits for your chickens.

Fruiting Vines

Plants like pumpkin and sweet potato, or even non-trellised cucumber, are effective living mulches. Plant them in an area where the root system will be happy and let them ramble. They work really well in food forests and backyard orchards as the vines give you both food and mulch, making the most of space when it’s limited.

Some plants, like nasturtiums, produce a prolific amount of seed each year

Interplanting Annuals

Creating a living mulch in your annual garden beds is a little trickier if you want to be able to clear them periodically or practise crop rotation. A solution is to interplant your annual vegies together so that you are using low-growing vegetables around taller ones. Plants that are great for this are lettuce and other leafy greens, bush beans, carrots and beetroot, but you can pair anything together as long as you take into consideration the soil and growing needs of each.

Chop And Drop

Some living mulches can also be cut and used as a chop- and-drop mulch. Comfrey, lemongrass, turmeric, vetiver grass, bana grass, broad beans, buckwheat and other traditional green-manure crops can all be used successfully in the right context. The key is to get your ‘chop’ timing right to avoid the green-manure crop going to seed or to allow plenty of time for the chopped foliage to grow back. Lay the cut leaves on the soil surface to mulch beneath the plants and to feed the soil as they decompose.

This article represents the permaculture principle OBSERVE AND INTERACT.

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