Why keep our compost worms in a box when they are probably happier in the ground? In-Ground Worm Farms do just this, bringing our worms down into our gardens.
The size and shape of IGWFs vary greatly, but they all share the same basic design. The top and access lid sit above garden level with the open bottom and perforated lower sides buried into a garden bed. Unlike conventional ‘captive’ worm farms, with liquid trays at the bottom, the worms are free to come and go as they please into the surrounding garden.
This freedom means the worms are less dependent on us to meet all their needs. If we don’t feed our worms regularly, or let things dry out a bit, the worms can just vacate to the surrounding garden bed, taking some of the pressure off us, particularly in hotter weather.
Collecting finished worm castings will be tricky and we won’t get any leachate (‘worm wee’ – worms don’t actually urinate) from the bottom of an IGWF, like we would with a conventional worm farm. The general idea is that the worms take the nutrient from the IGWF out to the surrounding garden.
The problem with this ‘theory’ is the confusion of compost worms with earth worms; quite different species, playing quite different roles in our soil’s life. Small, soft-bodied compost worms that are well suited to breaking down organic matter in our composts are not the same as the larger, tougher-bodied earth worms that push themselves through our garden soil, eating, aerating and fertilising as they go.
So don’t expect the compost worms in a small IGWF to spread fertility all though a large garden bed, and do expect a nutrient hot-spot (and a root attraction zone) directly under an IGWF.
Compost worms work best just below the surface of decomposing organic matter, so the surface area of a IGWF is critical, determining just how much organic material our worms can process.
The surface area of an IGWF varies from smaller home-made designs using a 100mm diameter PVC pipe, or an up-cycled food-grade bucket (250-300mm diameter) to small round units – sold with names like ‘Worm-Buffet’ and ‘Worm Feast’ (at about 300mm diameter) – right through to larger rectangular units, like the now defunct ‘Subpod’ (see pic) or the ‘Cool Seat’ (the size of a drinks cooler).
Smaller diameter IGWFs will only be able to process a very small volume of food scraps before the effective worm-active surface area is filled. So, unless we generate very few food scraps, or we are happy to have dozens of little IGWFs dotted around our garden, we are probably better off going for a larger diameter unit.
In operation, IGWFs are run much like a standard worm farm, so look up previous ‘conversations’ on these topics for tips on how to feed and care for your worms and provide ‘worm blankets’. And remember, like all compost systems, a balanced recipe, moisture and density are still essential for a well-functioning IGWF.
– Joel Meadows works with *Yes In My Back Yard, (YIMBY), a community-scale composting initiative in Castlemaine and surrounds. Send questions or comments to hello@yimbycompost.com, or to book in for a compost workshop.
