Reviewing Troy-Bilt’s Lithium-Ion Cultivator got me to thinking more about the impact of invasive gardening techniques on our friends, the earthworms. So I started digging :-P

Here’s what I found:

  • It depends on who you ask but there between 2700 and 7000 species of earthworms.
  • They were brought to North America by European settlers.
  • They are bad for some forest ecosystems but do a great job amending soil for gardeners.
  • You know  you have good soil if you have lots of earthworms.
  • Large-scale produce farms that do a lot of deep tilling and row cultivation don’t have many earthworms.
  • No-till or low-till farms maintain better conditions for earthworms to populate and fertilize the soil.
  • Earthworms are seasonal; they are most active in damp springs and falls. They tend to burrow deeper in dryer summers and winter.
  • Earthworms will die if they don’t have enough moisture or if the soil temperature isn’t within their range (again, it depends on who you ask and the specific earthworm species but seems to be between 55 and 70F).
  • They can be classified into 3 burrowing types: surface, shallow and deep dwelling.
  • Most can regenerate tail ends that get chopped off by birds but you’re not likely to get two whole earthworms from one. Each species has a different number of segments and their regeneration ability depends on what segment(s) get cut off and their own ability to regenerate.
  • Species commonly referred to as red wigglers are used in vermiculture (kitchen compost bins) and [edited: JMM] usually consist of two common species, one is an Epigeic worm and the other is considered an Epi-Endogeic worm. are NOT soil dwelling worms. Eisenia fetida falls into the Epigeic category (see next section below), is a compost/organic matter dweller, and is not found in soil. If you release them to the soil in your garden and they do not find a healthy compost bin or plenty of organic matter, they will die wild because they are not adapted to soil temperatures or the low levels of organic matter found in soil. The other species you’ll find categorized as a red wiggler is the Lumbricus rubellus, an Epi-Endogeic worm that prefers leaf litter, compost and lots of surface organic matter but also can be found in the top few inches of soil especially if the soil is rich in organic matter. [More info about red wiggler species.]

To avoid harming your earthworm population and to encourage them to thrive, we need to look at the habits of the three burrowing types:

  1. Surface dwellers (Epigeic species) Lives at the surface, usually in forest leaf litter. Small and adapted to variable moisture and temperature. Also found in compost piles because they are unlikely to survive in soil due to the lower organic matter. Red wigglers fall into this category.
  2. Shallow dwellers (Endogeic species) Lives in the top level of soil, usually down to 12 inches. They don’t have permanent burrows like the deeper night crawlers but rather they just burrow as they go in search of organic matter. They leave a trail of castings and slime in their wake. These are the ones you’re most likely to run into when digging or shallow-cultivating soil. They are most active in the spring and fall. Because summers and winters are dryer with more temperature extremes, they move deeper (~18 inches) into the soil to protect themselves. Dryer seasons are an ideal time to cultivate soil or plant shrubs and perennials that require deeper holes.
  3. Deep dwellers (Anecic species) These are the night crawlers, some of which have been known to burrow as deeply as 8 feet.  They maintain permanent burrows that are usually a straight shot down from the soil surface. They pull surface litter into their burrows where they munch in peace. You know  you have night crawlers if you find plugs made of soil and minerals throughout your lawn. The plugs protect the entrance to their burrows. Night crawlers also tend to be more active in spring and fall.

Soil management affects earthworms in several ways:

  • Affects food supply: No-till land will usually provide more food for earthworm populations than land that is cleared and plowed seasonally.
  • Mulch affects moisture and temperature: Leaving plants in an area also acts as a natural mulch that protects earthworms against sudden changes in soil temperature and moisture.
  • Chemicals: Impact of chemicals varies with the chemical. Read the first article linked in the biblio below for more details.

My hope is that with this info gathered in one handy spot, vegan gardeners can judge better how they are affecting earthworms in their gardens. Realize too that not all digging will kill earthworms. Knowing the seasonal dryness and temperature of your areas will help you determine the best methods for care and feeding of your garden buddies. Of course, there are other organisms dwelling in the soil and this post doesn’t begin to scratch the surface on the rest. I’ll try to post follow-ups by spring so we can be better informed before the next garden season.

Information above was gathered from University Extension research at the following links:

And you can read more about how earthworms are affecting forests here: