Earthworms - Nature’s plough | Gardening Lessons

Earthworms are sometimes called “nature’s plough” as they burrow through and turning over the soil in our gardens and fields. They’re also known as “ecosystem engineers” due to their importance in soil health and nutrient recycling.

You’ve probably seen worms when you were digging in the garden or perhaps they were wriggling along the soil surface.

But did you know that Britain has some twenty seven indigenous, or native species, of worms?

These are made up of different types of worm, not all live in the soil. Interestingly about 95% of the earthworm population is made up of only 10 of the worm species. But to make our lives simpler (as we’re not all earthworm specialists) its helpful to know that the worms are divided into four main groups, depending on where they live and how they act.

Epigeic Earthworm

These tend to live in the leaf litter on the soil surface which is also their food. They are red or red- brown in colour. It’s not surprising to learn that these worms are most usually found in woodland habitats and where the soil has a lower, more acidic pH.

Endogeic Earthworm

Pale in colour, these earthworms make horizontal burrows in the soil, often quite deeply. They are most often found in cultivated soils with a higher pH. For example, arable farms, pasture land, and amenity grassland. This latter are places such as playing fields and golf courses.

Anecic Earthworm

The lob worm (Lumbricus terrestris) is Britain’s largest earthworm at up to 35cm long. With dark heads these worms make vertical burrows into which they pull down leaves to eat. These are the worms most likely to make worm casts.

Compost Earthworm

Lives in compost bins and wormeries; and feeds on decomposing organic matter rather than soil. For example, red and stripey brandling worms (Eisenia fetida)

Where are the worms and why do we need them?

If you’ve been cultivating your garden and adding organic matter or compost to your soil you should see worms wherever you dig. You could do a little trial (see section below) and discover if the different areas of your garden have a similar number of worms.

NB – Many earthworms become semi-dormant over winter and keep warm under the soil or in the centre of a compost heap, so you’re less likely to see them.

If there are areas which have none or very few earthworms, you may like to think about why that could be so. Is it an area with established shrubs that haven’t had any extra organic matter added since you first planted them? Or perhaps you’ve only added inorganic or chemical fertilisers?

Earthworms are very sensitive to physical and chemical changes in the soil and dislike the often salty chemical fertilisers which may be added to feed a plant in the short term rather than to improve the soil and plant health in the longer term. A few inorganic fertiliser feeds are not likely to do much harm; it would be the sustained use which affects the worms and the soil, and therefore the plants.

Charles Darwin and Earthworms

Charles Darwin estimated that arable land contains about 53,000 worms per acre. More recent studies suggest that he underestimated this and the figure is nearer to 500,000 worms per acre. The more fertile the soil the more worms will be found.

In 1881, Darwin published his book on “The Formation of Vegetable Mould, through the Actions of Worms, With Observations on their Habits”. This was based on work in earlier lectures and publications which had been of little interest to the scientific community.

A note of explanation – the Victorian gardeners’ “vegetable mould” was what we today call humus-rich topsoil. And it was when Darwin aimed the work towards gardeners from the mid 1840s that the benefits of worms in the soil started to become accepted. From being considered only as fish bait and hen food, or worm casts as a nuisance on perfectly manicured lawns (sound familiar?) the worm turned (if slowly) into a soil hero.

Earthworm Experiments

Or rather, carrying out an earthworm survey in your garden. Personally I find this fascinating, but I appreciate that not everyone likes worms! We sometimes carry out this survey as part of the Year in Your Garden Course, and it is also a fun thing to do with children.

Imperial College led OPAL (open air laboratories) a UK wide initiative to enable anyone to get involved with scientific research about nature – earthworms in this instance. I’ve included links at the end if you want to find out a more detailed survey method, but a simple one involves –

Firstly marking off a square foot / ½ metre of your garden for the survey area. Inside that area you then –

Dig a hole to take a soil sample
Investigate the properties of the soil sample – soil type, moistness, pH
Record the different species of earthworm and their numbers (link to a ID chart below)

Now that only tells you about one small area – it’s even more interesting to repeat in different parts of the garden. For example, does your vegetable garden have the same number of earthworms as the lawn?

Although there were issues with some of the results from the OPAL Soil and Earthworm Survey – largely from the identification of worm species they are still valuable. Over 5,500 responses were submitted and it showed that domestic gardens were far more likely than other habitats to have a good sized earthworm population. Rural gardens scored higher than urban on both population and species numbers.

Hibernating earthworm, by Rory Waterfield

Earthworms – the Soil VIP

So why are earthworms so important? Briefly, their burrowing in the soil to move around creates channels for air to circulate and water to drain through. They will either push through with their heads if the soil is soft, or literally eat a way through if the soil is more dense or compacted.

Some of the tunnels can be a few feet deep, this is especially important for those who garden on heavy, clay type soils as such deep and constant activity really improves the soil quality. Plants need air at their roots in order to breathe and they need water; soil air and soil water fit in the spaces between the soil particles. Worms help to create those spaces and to maintain them.

Compost Bins, Worms

Worms are also a great help in your compost. They eat the organic matter, the vegetable peelings and dead flower heads, and help the process of turning it all into a friable consistency ready for you to use in the garden, full of nutrients.
Earthworms such as brandling worms are the best worms for compost bins. If you have or want to get a wormery, then you do really need these compost experts working in there for you.

Wormcasts

The worm casts which you may see on your lawn or border are the worm’s poo. This waste matter is rich in nutrients otherwise unavailable to plants and is richer than the surrounding soil. It makes a wonderful natural fertilizer. The worm casts can be easily broken with a trowel or hoe, left on the surface for the rain to wash through the soil or lightly forked in next to your plants. The casts can be added to potting mixes if you make your own. They are pH neutral and richer in nutrients than the most fertile soil, so a little goes along way.
So next time you see that your lawn is covered with lots of worm casts, don’t get angry, get out there and brush that goodness into your borders for your plants to feast on!

And finally…

You know when children ask you difficult questions such as “which is the head end of an earthworm?” You confidently reply “the pointy end” – guess what – you’re correct!

The comic illustration of an earthworm hibernating is from our eBook “In Your Winter Garden” and is drawn by Lucy Waterfield aka Rory Waterfield

If you would like help with learning more about your garden and gardening, why not ask about our bespoke Gardening Lessons, where your classroom is actually your own garden. We can help you learn gardening basics, carry out worm and other experiments and also show you how to plan an ornamental border or kitchen garden.

And for further gardening advice and inspiration, check out Plews Potting Shed blogs, including the selection below and our monthly Tipsheet – You could come and find us on Instagram Pinterest and Facebook too.