Living SoilDo you turn over a spadeful of soil and find no worms at all? Have you wondered whether you should just buy a box of them and tip them in?
Few worms is a sign worth noticing. Healthier soil has more soil organisms such as earthworms, along with better crumb, a darker color and more roots. But the answer is rarely to bring worms in. It is to make the soil somewhere worms want to be.
Are earthworms good for soil?
In the garden, the research says yes. Earthworms convert dead and decaying matter into castings, worm manure rich in nutrients that plants can take up more readily. Those castings help form soil aggregates that let air and water into heavy soils.
Their travels matter too. Tunneling lets air and water in and improves drainage and tilth. Earthworms pull organic matter below the surface, where other decomposers can reach it, and bring soil from deeper layers up toward the top. Over time, earthworms and other soil organisms work surface mulch into the soil, much as happens on a forest floor.
The big idea: you do not add earthworms to good soil. Earthworms show up in soil that feeds and shelters them, and then they make it better still.
How to attract earthworms
Feed them with mulch
All earthworms eat organic matter. Leaf litter or compost on the soil surface gives them a good source of food, so use plenty of organic mulch.
Keep the soil damp
Drying out is a hazard for earthworms. They need plenty of damp soil to stay healthy.
Dig less
Repeated rototilling can compact the soil just below the tilled layer, reduce the pore space for air and water, and kill earthworms. Nightcrawlers are especially sensitive. They are vertical burrowers that can go down as far as 8 feet in damp soils, and tilling destroys their permanent burrows.
Go easy on pesticides
Some fungicides and insecticides can be highly toxic to earthworms and can suppress, or nearly eliminate, their populations. Even when pesticides do not kill worms outright, they may concentrate in the worms' bodies. Reducing or ending pesticide use is one of the ways extension advice gives to make a yard more comfortable for worms.
Avoid sudden pH swings
Earthworms tolerate a wide range of soil pH, from 4.5 to 8.2, but they cannot stand rapid changes. So if you change your soil's pH, avoid sudden swings.
Should I buy worms for my garden?
The extension pages we read do not review buying garden earthworms by mail. What they do say is clear enough. Instead of transporting earthworms to your garden, it is better to invite them in by making it more hospitable. Simply adding worms will not make great soil. It is up to us to give them clean, undisturbed soil and plenty of organic material to eat.
Composting worms are a separate case. Nightcrawlers will not live in a worm box, and the worms that do belong in a bin are covered in worm castings and worm composting.
Here is where the sources differ: not every worm is welcome
Garden pages call earthworms such as nightcrawlers beneficial. The same research also warns that in northern states and Canada, non-native earthworms threaten forests by breaking down the leaves and debris on the forest floor. Both are true at once: worms help a garden bed, and they can harm a natural forest.
So never release an earthworm in a natural forest. If you use worms for fishing bait, throw any unused ones in the trash.
The jumping worm caution
Watch for jumping worms. Jumping worms (Amynthas agrestis, Amynthas tokioensis and Metaphire hilgendorfi) threaten home gardens, farms and woodland. They deplete soil nutrients and reduce the soil's ability to hold moisture, and over time the soil begins to look like coffee grounds.
How do you tell them apart? Look at the clitellum, the band around the body. On a jumping worm it is pale and flat and goes all the way around. On a common earthworm it does not go all the way around, and it is darker and slightly raised.
Jumping worms, at any stage of life, can arrive in soil, compost, mulch and manure delivered to the garden, and they hide in the soil of potted plants. Check what you bring in.
There are currently no approved pesticides or other treatments to prevent or eradicate them. If you find them, you can hand pick them and drop them in a bucket of soapy water. For a pile of material you suspect, one extension page describes leaving the enclosed pile in the sun for 2 to 3 days: the inside has to go above 105 degrees Fahrenheit to kill the worms and their cocoons.
Where to start
Spread a layer of leaf litter or compost over bare soil, keep it damp, and put the tiller away. Check new soil, mulch and potted plants for jumping worms before they go in. Then read mulch for healthy soil and what the soil food web does.