“I doubt that there are many other animals which have played so important a part in the history of the world” said Charles Darwin of the earthworm. More descriptive perhaps, Aristotle called worms the “guts of the earth.” In either case, it is apparent that these little critters below our feet have been recognized for their valuable contribution for centuries. If you see lots of earthworms in your garden soil, be thankful and congratulations! It's a sign of healthy soil, one of the key elements in growing good roses, or any other plant. They can eat their weight in decaying plant matter each day
For most gardeners, earthworms are a common sight, and one to be encouraged. What do earthworms really do? Lots of good things to the soil including:
Mix and aggregate the soil - As they consume organic matter and mineral particles, earthworms excrete wastes in the form of casts, a type of soil aggregate. The burrowing action of the worms moves soil particles closer together near burrow walls, and the mucus secreted by the worms as they burrow can also help bind the soil particles together. By mixing the soil, they help achieve the proper air, water, and solids ratio for maximum plant growth.
Stimulate microbial activity - Although earthworms derive their nutrition from microorganisms, many more microorganisms are present in their feces or casts than in the organic matter that they consume. As organic matter passes through their intestines, it is fragmented and inoculated with microorganisms. Free-living nitrogen fixing bacteria (good for plants) are more numerous around the sides of earthworm burrows.
Increase infiltration – The worms maze of tunnels increases the soils ability to absorb water. Some species make permanent burrows deep into the soil. These burrows can persist long after the occupant has died, and can be a major conduit for soil drainage, particularly under heavy rainfall. At the same time, the burrows minimize surface water erosion. The horizontal burrowing of other species in the top several inches of soil increases overall porosity and drainage.
Improve water-holding capacity - By fragmenting organic matter, and increasing soil porosity and aggregation, earthworms can significantly increase the water-holding capacity of soils.
Provide channels for root quality - The channels made by deep-burrowing earthworms are lined with readily available nutrients and make it easier for roots to penetrate deep into the soil.
Bury / shred residues - Plant and crop residue are gradually buried by cast material deposited on the surface and as earthworms pull surface residue into their burrows.
Neutralize soil pH - Analysis of earthworm castings, or earthworm manure, shows that the soil that comes out of the back end of an earthworm is closer to a neutral pH (7) than what goes in the front end, regardless of whether the existing soil is above or below pH (7). This is achieved by the action of the worms calciferous gland and the buffering action of carbonic acid. Soil which has passed through the gut of an earthworm shows much more available phosphorus and potassium than the same soil which has not passed through the worm.
Reduce harmful nematode populations - As yet, the exact reasons are unclear, but soil with earthworms invariably has less harmful parasitic nematodes than soil without earthworms.
Improve overall soil quality - The activity of the earthworm gut is like a miniature composting tube that mixes, conditions, and inoculates plant residues. The earthworm removes plant litter from the soil surface, turning it into free manure. It has been demonstrated that earthworm castings contain about five times the nitrate, seven times the available phosphorous, three times the exchangeable magnesium, eleven times the potassium and 1.5 times the calcium as regular soil. Research has also shown that microbial activity in worm castings is 10 to 20 times higher than in the soil and organic matter that the worm ingests.
There are two major types of earthworms – the deep-burrowers ("nightcrawlers") build large, vertical, permanent burrows that may extend 5 to 6 feet deep or more; they pull plant residues down into the mouth of their burrow, where the residues soften and can be eaten at a later time. The shallow-dwelling worms (known as redworms, grayworms, fishworms, and many other names) are comprised of many species that live primarily in the top 12 inches of soil. Adults are usually 3 to 5 inches and they do not build permanent burrows; they randomly burrow throughout the topsoil, ingesting residues and mineral soil as they go.
Nightcrawlers tend to be more active in spring and fall, but they may not go into a complete resting state in summer or winter since they can retreat to the bottom of their burrows during extremes of heat or cold. New worms will generally only emerge when soil moisture and temperature conditions are suitable.
Earthworms thrive best on organic debris that contain a high percentage of nitrogen. This is encouraged through the addition of organic soil amendments and mulch. Water is also a major necessity of earthworms as they contain about 80% water by weight and lose about 15% per day. If moisture is not available they will dig deep into the soil to find it. Simply adding earthworms to poor soil won’t do much good. However, if you add organic material to you soil, chances are the worms will come. So, it is pretty easy – just add organics when planting or mulching, and keep things watered – and the worms will come.
Earthworms are truly the gardeners best friend. And one last added benefit ... they provide free fishing bait!