Mulching – flowering bean organic gardens

Unseen below ground is a vast world, teeming with life. Well at least we hope so… but sadly so much of our soil is now depleted. However, we still have time to restore the richness of the soil by increasing the crucial levels of beneficial microorganisms, fungi, and bacteria.

But what about the humble earthworm – including our native species? Like most gardeners, I’m excited to see earthworms in the garden and wonder if we tend to know intuitively that they are good for fertility and soil health, but I suspect most of us know very little about them. To delve into the topic of earthworms, I talked to Prof Steven Trewick, Professor in Evolutionary Ecology at Massey University.

Earthworms are specialists

Earthworms belong to the group of invertebrate animals known as annelids, or segmented worms, which include more than 20,000 species around the globe. They are highly diverse in the way they live, but because they dehydrate in the open, they are constrained to living below the surface of the soil or in the sea.

Trewick describes how earthworm species are specialised to different areas and the ground can be partitioned into three zones where the different species live:

Epigeic earthworms live in the surface and leaf litter area and break down dead organic matter.
Endogeic earthworms live in the in the topsoil layer and create horizontal burrows.
Anecic earthworms live in the lower level of subsoil. They make permanent vertical burrows and glean nutrients from minerals and organic matter. These subsoil species can be big and include a bioluminescent species of native worm known as Octochaetus multiporus that can grow up to 30cm long¹.

Some of the introduced worms are specialists of pastures and others thrive in gardens, while the tiger worm mostly lives in compost heaps and doesn’t do well if moved into the garden. As Trewick says, it shows us how different the ecologies of different species are.

New Zealand’s native earthworms

Aotearoa New Zealand is also home to around 180 native species of earthworms and Trewick says we are finding more species all the time. The native earthworms belong to the family of Megascolecidae, and they live across our country’s forestlands.

However, Trewick says we don’t know if native worms are surviving around the country, and the general view is that as you get into pasture and urban areas the native worms disappear. But those are two correlated observations (one observation that appears to be related with another), and it might not be completely cause and effect; there may be more going on in the deeper soil. However, these days when we see a worm in our gardens or above soil after rain, it is likely to be one of the introduced Lumbricidae earthworms. These species were brought to Aotearoa New Zealand from Europe.

Garden fertility and earthworms

Worms create burrows and pores in the soil, which aid growth by aerating the soil and creating space for water and root growth. They also break down, move and recycle organic matter, creating richer and more diverse soil structure which is very important for plant growth. Pavlis (2020) suggests the microbial activity in worm casts is 10-20 times higher than it is in soil.² Trewick says, that like every animal on the planet, it’s the microbiome associated with their gut that enables them to do what they do.

The study of soil microbiology, earthworms and fertility is complex and ongoing, but most of gardeners and growers will agree, the presence of earthworms is a pretty good sign in a garden.

How can we support earthworm populations?

To support earthworms, first and foremost, we need to think of our gardens as habitats. Trewick says, “Diversity is the answer; the garden shouldn’t be thought of as some sort of clinical formalised arrangement of things. You have to allow the process to work. Having a messy garden is good for diversity. We have to share the space a bit.”

“It’s not how you grow stuff, it’s how you dump stuff!”

This fantastic quote from Trewick is a perfect way to describe what we need to be thinking about in our gardens. Aim to always be increasing organic matter — mulch, mulch, and more mulch. This has several functions; it keeps your soil moist, providing a safer environment for the worms and microbiology; and it provides organic matter and food. This in turn decreases the need to cultivate, which helps increase your worm population. Read more about mulching here.

To support earthworm populations Trewick suggests that gardeners:

leave things to break down, be it a pile of logs or leaf litter
keep the circle of fertility going by giving back regularly
keep compacted areas to a minimum – reduce pathway size between beds and keep heavy machinery off your gardens
use low or no till to reduce the disturbance to earthworms and microorganisms
reduce or stop using pesticides and herbicides.

Perennial plants are also a bonus for earthworms because you can create undisturbed habitats where they can thrive. You can read more about perennial plants here.

How can we design our gardens to support earthworms?

The edges are an importance part of our human spaces. The edges are where diversity can thrive; our forests and scrub edges encourage a crossover of diversity into more cultivated areas. However, Trewick says, one problem is our large-scale paddocks as they can be overwhelming to native fauna.

In a home garden too, when we design our vegetable patches as highly controlled zones, surrounded by single species lawn and clipped hedges, we are reducing habitat. Trewick suggests, if we do feel the need to control the vege or flower patch, we can have ‘messy’ edges where biodiversity can flourish. Who knows, maybe there might be some bio-luminescent native earthworms trolling down there!

Messy edges in a home garden can support earthworms

Further resources

Wild Life New Zealand Textbook focusing on the unique plants and animals of Aotearoa by Trewick, S & Morgan-Richards, M.
Phoenix Group Evolutionary Ecology & Genetics @ Te Taha Tawhiti https://evolves.massey.ac.nz

References

Science Learning hub (2018). Octochaetus multiporus. sciencelearn.org.nz/resources/21-octochaetus-multiporus ↩︎
Pavlis, R. (2020). Soil Science for Gardeners. New Society Publishers ↩︎

What are perennials?

Perennials are plants that grow for more than two years and, while we often think of perennials as trees and shrubs, some vegetables are also perennial. Perennials can be evergreen and keep their leaves all year round, or herbaceous, i.e. their tops die down in winter and their roots stay alive and come away in spring.

Why plant perennial vegetables?

In the garden, perennial vegetables offer some advantages over annuals. Once planted, you rarely need to disturb the soil which means soil life and microorganisms can do their thing while you nurture the plants above the soil and harvest their goodies. Perennials also provide habitat for animals as you are not replanting and disturbing them as often. Some perennials can survive long dry periods as they have deep root systems so the plants are better adapted to tap into deeper stores of water in tough climate times.

Designing with perennial vegetables

Decisions in the garden are continuous. However, initial planning design for perennials is important because some, like asparagus, you may have for 20 years or more.

One of the best bits of advice I have had is to consider water needs when planting perennials. Perennials generally require less water than annuals, so if you group annuals together it allows you to target your water use towards them and less on the perennials.

Perennials often require less maintenance, so they can be a little further away in areas you visit less often, such as the boarders of your garden. However, it is also wise to check whether they have the potential to take over a space and so require a bit of thought before planting.

Asparagus pushing through the soil surface

Mulching, weed control and fertilising

Perennials benefit from a good mulch. Mulching adds nutrients, helps retain moisture in summer, reduces leaching from heavy rainfall and reduces weed competition. Some perennials can be cut back and used as a mulch, which also returns some nutrients back to the soil. Asparagus fronds are a good example, they can be chopped and dropped in place when they turn yellow in late autumn. You can read more about mulching here.

Weeds can be hard to eradicate with perennials as you don’t want to disturb and cut the roots of the plants trying to pull out deep rooted weeds. Weeds can also get well established before you notice them as you tend to check perennials less often than annuals. Getting to the weeds early and providing a good layer of mulch can both help with weed control. Although I must admit, my asparagus seems to be surviving the onslaught of weeds that I never seem to get to!

Perennials do need feeding, especially when you are harvesting from the plants. Well made compost and mulching increases organic matter and both help feed your plants. I also use a good quality seaweed fertiliser.

Some perennials can be cut back to provide compost materials. For example, once the Jerusalem artichokes have finished flowering and die back, I prune them down and use them as a carbon source in my compost.

The lush growth of asparagus in summer with
flowering jerusalem artichokes in the background.

Sourcing perennial vegetables

Perennial vegetables are not always easy to source, but the search is worth it. Most of our perennial vegetables have come from specialty stores and some from friends. We grow asparagus, sorrel, jerusalem artichoke and New Zealand spinach. Some plants are available in general garden stores, but it is worth looking at online specialty growers and definitely your friend’s and neighbour’s gardens.

Dividing perennials and sharing them around serves two functions, keeps you and your friends supplied in plants and also stops overcrowding.

Happy gardening

Tag: Mulching

The Hidden World of Earthworms

Perennial vegetables

Mulching, weed control and fertilising