Tuesday 7 May 2013

Wonderful worms

I am passionate about earthworms. Just ask my former students!  A few years ago, the New Scientist reviewed a delightful book about worms by Amy Stewart. I recommend  it. It’s called ‘The Earth Moved’. Un-be-known to me, Brenda noted it as a potential Christmas present. She went to the bookshop and the assistant checked on her computer. “Oh yes madame, we have it, you will find it in Fiction!”

Minimum cultivation methods are repeatedly shown to increase worm populations. Why are those people who care about worms, not up in arms about soil cultivation which destroys worm habitat? Where are the protests against rotavators that shred worms?

This March, all soil surfaces in my zero cultivated, glyphosate-sprayed, cemetery garden were completely covered in earthworm casts.
Worm populations
These are hugely variable and dependent on a myriad of factors such as  rainfall or drought.The following numbers of worms per square meter are a very rough guide -
  • cultivated soil, 150 
  • no till management, 300 
  • grassland, 500, often considerably more
Counts in excess of a thousand per square meter are not uncommon. Darwin was wrong! Never did I think I would write these words about my all time hero who did more than anyone else to research and promote the merits of worms. It’s just that even he underestimated how many worms there can be. Agricultural grassland can contain a greater weight of worms than the cattle that graze!

Benefits of worms
There are many species of worms. More than 150 of horticultural significance worldwide. All have varying habitats, many in most unlikely places. Perhaps the two most common to gardeners - both usually graced by their latin names - are the night crawler, Lumbricus terrestris and the brandling or tiger worm, Eisenia fetida. The night crawler may be found all the way down to a couple of meters, whereas eisenia is found in decaying vegetation and manure and barely survives in a mineral soil.
The benefits of worms to are huge.
  • Their tunnels permeate the soil and provide aeration, drainage and easy root penetration.
  • It has been pointed out by Bill Mollison, a founder of Permaculture, that as worms move through the ground they act like pistons sweeping air through their tunnels.
  • They redistribute organic matter and in particular pull surface vegetation into the ground.
  • They intimately mix soil particles and organic matter in their gut. They create water-stable aggregates (crumbs) of sand, silt and especially clay.
  • Nutrients are concentrated in their castings. Compared with figures for surrounding topsoil there are enhanced levels, typically nitrogen x 5, phosphate x 7 and potash x 11.
  • They shift soil! A  single worm might cast as much as 5kg of soil in a year!
  • Some species destroy harmful soil nematodes in their gut.
  • Their casts are rich in biologically active microbes.

It’s not all good
Could it be that worms are ever unwanted?
  • Because some worms cast at the soil surface green-keepers do not like them.The same casts are of huge benefit when they occur in the none-digger’s vegetable garden when he wishes to make a tilth. For the domestic lawn, I believe worms to be beneficial. I was a little taken aback at the criticism of my recent  post when I mentioned that my use of iron sulphate as a moss killer also discourages casting worms. My critics have a point, but I would argue that the effect of iron sulphate on overall worm population is small and does little harm to the deep crawlers. The surface casting types - the minority -  just migrate to my borders. Compared to the huge shifts in worm populations caused by the environment and meteorological factors the detrimental effects of a gardener’s activities such as his limited use of fertilizers and weedkillers is small.
  • Some gardeners worry that worms might clog the drainage holes in their pots. I have no such concerns and just ignore them.
  • The burrows they create has been known to destroy earth dams!
  • As described in Amy Stewart’s fine book, introduced none-native worm species, can destroy natural woodland habitat. Worms’ very efficiency in mixing organic matter into the soil removes surface decaying vegetation, the natural niche for many wild plants.
  • They bury things! I am being a little frivolous here! My thirty year old rock garden stones in my previous home virtually disappeared! Whenever I shift logs that have been standing on the ground I see evidence of the soil that earthworms move. Could worms be a partial cause of the burial of archeological remains?
The base of my log-pile becomes infiltrated with worm casts. Here an upturned log exposes casts on the ground
But some good news for gardeners!  Although many fine public gardens are host to the New Zealand flatworm, (they just don’t tell you), this dreaded nematode predator of worms is not proving to be the scourge we once feared.

What can the gardener do to encourage worms?
  • Don’t dig!
  • Leave dead weeds, leaves and other  organic debris on the soil surface.
  • Mulch.
  • Many worms like a neutral or slightly alkaline soil. Their digestive juices need  calcium. On acid soil applying lime may help.
  • Grow plants! Perhaps in my post about green manure I neglected to mention how  good it is for worms. And they love clover!
  • Add garden compost and well rotted manure.
Worms like untidy gardeners


  1. I love worms too. They do a great job for me by converting kitchen- and garden waste into compost. My compost bins are literally "heaving" with them. There must be many thousands in each bin. Unfortunately the local badgers also know this...

    1. My friend in Preston has a worm bin and has promised me some photos which will be great for a future post

  2. So worms are really fictitious are they?

    1. Well I did say I was passionate about them Sue!
      The Earth Moved is a splendid title of a book about worms but I expect anyone hunting the fiction section for a steamy novel might be disappointed

  3. I LOVE worms- and now I have learnt about their nutrient-rich castings I love them even more. The burial thing is a bit of a worry though... we have a lot of worms here and I have a suspicion that they may have buried several pairs of secateurs over the years :-/

  4. I found a three month lost pair of felco secateurs in some leaf litter last month. With a great deal of poetic licence I might claim that the worms as they buried leaves found them for me!
    They are well oiled up and are working fine- the secateurs I mean!

  5. I have noticed the past few weeks that there are no earthworms out crawling around after rain. None. I haven't seen any this summer. Why? I live in southeastern Pennsylvania. What's going on - or not going on?

    1. Good to hear from you over there! I googled 'pennsylvania no worms' but no luck, but there was an excellent article about worms as the top hit by Penn State University! It does not appear you have a special worm problem (other than worms introduced by fishermen into natural woods)
      I cannot answer your query anon -except in general terms. I guess the answer lies in your weather. It is common when very dry for worms to go deep (it might take more than a shower to bring them to the surface). Excessive wet or dry ,warm or cold all effects where worms go.

  6. The fresh and attractive looking worms makes it easier for the fisherman to catch the prey.

    1. Yes and xxxxxx fisherman have in parts of the US introduced worms into inappropriate ecological situations!

  7. I couldn't decide if I should post this here, a couple of years too late, or on the more recent Soil Carbon Capture where it is off topic. I decided here was better!

    My neighbour was digging her veg patch a couple of days ago. Unlike my heavy solid stuff, previous gardeners have worked miracles on her soil. I watched in envy. But I noticed another big difference in our soils. Mine has so many worms that even the smallest hole dug will cause carnage. And if I peek under any of my cardboard mulch, there are some huge beasts that could almost be mistaken for slow worms which shoot down holes that are so big it's hard to believe that worms made them. I didn't know that worms could move that fast either, but they can. My estimate would be that I have at least ten worms to a spade full, probably more. Watching my neighbour, I saw about one worm to every five spades full that she turned over and broke up. One worm to my fifty.
    I don't suppose having the most worms makes me the winner just yet, but it did give me encouragement that my worms are loving it, breeding like crazy, and their hard work is going to get my soil 'dug' in no time. Neighbour on the other hand is now very worried about her lack of worms!

    1. It's great to have comments on old posts Sarah,it helps keep them alive.
      Better tell your neighbour to stop digging! Your cardboard must be working wonders!


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