Earthworms in the Vegetable Garden
It’s a team effort:
The gardener is rarely alone in the garden, even when there is no one else in sight. That’s because there is a large and busy unseen work force just inches away toiling at tasks that help make the garden a success even though said work force has no idea that it is doing so. We refer of course to the lowly and much underrated earthworm, unseen ally of every gardener who ever wielded a hoe.
Earthworms when present in the garden in adequate numbers keep the soil loose by burrowing through it. They eat particles of sand and clay as well as microorganisms and organic matter and excrete what is in effect a highly balanced plant fertilizer. They migrate from the topsoil to the subsoil and back bringing nutrients closer to the plant roots where they may be easily utilized. Their tunnels create arteries through which air and water can pass. They might almost be gardeners themselves.
How many worms are enough worms?
There is almost no practical upper limit to how many worms a garden can benefit from. One way to find out if there are enough present is to take what Edward C. Smith in his excellent gardening handbook, “The Vegetable Gardeners Bible” refers to as a “worm census”.
Mr. Smith states that a worm census will be most accurate if performed in the spring or fall, and not in the blazing heat of summer which tends to drive worms in unmulched beds deep. Smith recommends marking a twelve by twelve inch area of garden soil and digging down seven inches or so with a spade. Transfer the soil obtained on to a plywood square or similar surface. Gently separate the soil and count the worms found – small worms count the same as large ones.
Less than ten worms in a sample of that size indicate a problem. 40, 50 or 60 worms indicate a large and lively work force, busily drilling tunnels and creating rich fertilizer. It also indicates that the soil has a good PH factor, adequate organic matter and a rich subsurface microbial life. It possesses good “structure”.
What about those tunnels?
When a worm squirms its way through garden soil it opens up pathways called tunnels which are beneficial for a number of reasons. The tunnels allow air, vital for photosynthesis and overall plant health to penetrate the soil easily and deeply. It opens drains for surface water; soil well worked over by worms can absorb water up to 4 times faster than can moderately compacted and relatively worm free soil. And the tunnels allow roots to penetrate deeply and spread easily, all of which leads to healthy and productive vegetable plants.
Natures own fertilizer:
Worms like to eat. They like to eat microbes and other subsurface life forms, particles of silt and clay, and decayed organic plant matter otherwise known as compost. As they do so they excrete pellets called castings. These castings make the soil more friable, which allows more space for air and water to penetrate, and as was the case with the tunnels makes it easier for roots to penetrate the soil.
But castings are much more than soil loosening granules. They are a potent, safe to use and highly beneficial plant fertilizer. The tiny pellets the worm leaves behind have elements of nitrogen, potassium, calcium, phosphorus, potash, and magnesium 5 to 11 times more concentrated than the original topsoil possesses. Moreover, in a single year, given a soil rich with humus or compost, a single worm can produce up to 10 pounds of casts. That is a lot of safe, effective plant nutrient.
If you build it, they will come:
How to introduce more earthworms into the garden might be an appropriate question at this point. It is simple; work lots of compost into the soil, as deeply as possible, and then mulch the beds.
The compost gives the worms plenty to eat, thus plenty to excrete, and encourages them to make many more worms. The mulch will keep the surface temperature and moisture level within acceptable ranges for earthworms and keep them near the surface of the garden, where they do their best work.
A nice experiment is to keep informal tabs on the compost heap as it progresses through spring to early summer. Turning after turning the gardener will notice progressively more earthworms, appearing as if by magic, in the compost pile. This is because for an earthworm, compost is a free banquet; they wriggle into it and happily produce more worms, which transfer to the garden as the compost is applied.
Things to avoid are excessive mechanical tilling and concentrated chemical fertilizers, both will kill and drive earthworms away.
The grower is never alone:
The gardener staking, weeding, trellising and watering without another soul in view may believe that his is a solitary endeavor, but unseen beneath that top layer of mulch, an army is at work on his behalf.
Earthworms: Wriggly Immigrants
The earthworms in the northern part of the United States and Canada are not native. Any earthworms which may have been indigenous to the land a million years ago were scoured away by the last ice age. The worms found in those parts today came in ships ballast, root balls on imported plants and as cocoons in domestic animals hoofs, with the first European settlers.
Their effects are not always beneficial. Invasive earthworms devastate hardwood forests by eating up, in no time at all, leaf litter and humus which the trees require to retain water, and for their own nutrition.
There are two sides to every worm.