Opening that can of worms

This is a must-read for all wildlife-friendly gardeners. Susan Harris of the Sustainable Gardening Blog has done a thorough job of researching all the ins and outs (as in "the worms go in and the worms go out) of composting with worms, including the vexing issue of whether vermicomposting contributes to the destruction of woodland ecosystems.

To summarize the high points: Earthworms change the soil. This is great if you grow vegetables and some conventional garden plants because earthworms produce the kind of soil these plants love. But it's not great if you're trying to protect a woodland ecosystem where earthworm activity has historically been very low. In woodlands, many plants rely on a thick layer of "duff" (organic material) in which to grow; high earthworm activity decomposes this duff too quickly, threatening the survival of many native woodland wildflowers.

As is so often the case, the species that present the greatest threat are not native to North America. Now, this much many of us already knew. But what Harris discovered in her research is that it is beginning to look as though the primary threat is one particular non-native: Lumbricus rubellus, aka the night crawler, the earthworm commonly used as bait. (The popularity of this worm as bait helps to explain why, unfortunately, it has been spread so widely.)

But there's good news for gardeners. According to Harris, the type of earthworm commonly used in vermicomposting does not present a threat to woodland ecosystems. That's because the red wiggler, Eisenia fetida, doesn't survive well in the wild.

Harris advises her readers to make sure they use only red wigglers in their composting efforts, purchasing them from reliable sources. My solution to this problem is simpler and cheaper: I use worms I collect in my own garden. That way I can't add any non-native species to the environment unless they were already there (and if they were already there, my composting efforts won't make any difference to the population). Of course, if you have no red wigglers in your garden, this may not work for you. But why not give it a try? The worst that can happen is that your initial vermicomposting effort will fail, and you will know that you have to purchase red wigglers.

Another good piece of advice Harris passes on in this article is to avoid dumping the contents of a worm bin in a wooded area. As a matter of fact, you should never dump any garden waste in any natural area.

Incidentally, ducks love to eat earthworms--especially those big, juicy nightcrawlers!


Sue said...

I didn't get that article read, so thank you for the summary. I had been thinking about doing something to increase my population of worms, but maybe I just need to keep composting, and hope they populate it.

Wild Flora said...

Hi Sue. To increase your population of desirable worms, generally all you have to do is feed your soil. If they're present in the soil, feeding them with organic material will encourage them to reproduce. To collect worm castings that you can then add to your garden, you can build or buy a worm bin, keep it well fed with kitchen scraps, keep it moist, and put it in an area where temperatures will stay above 40 degrees F. Under these ideal conditions, red wigglers will turn your kitchen waste into wonderful garden soil.

Sue said...

Thanks for your reply to my comment. So, if I continue to compost, and apply it to my garden, that should cause the worms to reproduce. Maybe I don't need to have the bin, then, except for being able to compost in the basement though the winter. I'll have to think about that.

Wild Flora said...

Dear Sue,
You got it. As far as I know there are really only three reasons to have a worm bin: One is to be able to continue composting your kitchen waste during the winter months, another other is to have a very high quality soil available for various purposes. I have to add, though, that in my experience the amount of compost that a single home worm bin can produce doesn't go far in the garden. It's nice to have available, but you will get far more benefit just from feeding the worms that are already in the soil. FYI, you don't necessarily even have to compost kitchen waste before you add it to the soil -- some gardeners just dig a trench alongside their vegetable plantings and bury kitchen waste directly in the soil.

If you're wondering what the third reason for having a worm bin is -- that would be to provide treats for your ducks!

Sarah O. said...

I appreciated learning that nightcrawlers are the main perpetrator when it comes to invasive worms, but I haven't read anywhere what the average gardener can do about it, or where the situation is most critical (forests with clay soil? Sandy? etc.). We have lots of nightcrawlers in our lawn and raised vegetable beds, for instance, but they hardly ever show up in our unimproved native clay soil beds on the side of the house. I have also never seen them in the soil in our woods. But should I be worried about them making it there eventually? And that's just small-scale. What does nightcrawler expansion mean for the entire boreal forest range, and are there areas where due to soil type, they probably won't advance?

There are still far too many unanswered questions for my liking!

Wild Flora said...

Hi Sarah O.,

There isn't much a gardener can do about invasive species AFTER they've been introduced to an area. Commentary about the damage done by invasives is mostly designed to scare us into trying to avoid spreading or introducing invasives in the future.

Sometimes it's possible to eradicate an invasive if it hasn't become well-established yet. But to get rid of non-native earthworms that are already thriving in a garden would be impossible. The best you can do is to avoid spreading them into areas such as woodlands where they may not be present yet.

Unfortunately, if nightcrawlers are like a lot of other non-native invasives they probably will spread, and it will probably be difficult to impossible to prevent that from happening. Sadly the day may come when some native wildflowers will be found almost exclusively in arboretums or in gardens belonging to particularly dedicated gardeners, just as many species of animals are now found almost exclusively in zoos.

Maine Worms said...

Nice Article. I raise and sell red worms and Euro nightcrawlers and have a beautiful garden with the castings. Do you know how long it would take to build up a good garden without the use of worms. Maybe you like those nasty chemicals, That are killing our children, pets, birds and all sorts of wildlife. Or you just want to throw your garbage in the landfill and make more Methane Gas.

Sarah O. said...

Hi Wild Flora,
I guess my main point is, I wish that the studies that confirm these worms are invasive (or the news reports about the studies?) also had an idea about advancement rates and if there are natural barriers to their advancement such as cold tolerance, soil type preferences, peat marshes, drout-prone areas, etc. Obviously I will do what I can in my own yard, but what does this mean for Canada's vast boreal forest (which is not a monolith)? It's just information that I like to have. :)

(An aside: am I alone in thinking Maine Worms did not read this post? Talk about arrows flying wide of the mark - wrong mark!)

Wild Flora said...

Hi Sarah,

Now I get what you're saying. It's tragic that we know so little about the effects of invasive species, present and future. The not knowing makes it very hard sometimes to know what is best to do in any situation -- I work on a "best guess" basis most of the time, myself. At the risk of seeming woo woo or weird, I'll say that I find that reading the Bhagavad Gita helps at times like these. But I'll have to save the explanation of that for a full post.

(As for MW, yeah, he does seem to have rather missed the point.)

Lynne said...

I'm with you! Native worms only!

Teena in Toronto said...

Happy blogoversary!

Wild Flora said...

Thanks Teena!
Two years today, and I hadn't even noticed until you pointed it out to me.