Once you've had a worm bin running for about three months, you'll begin to see that much of the original contents, such as food scraps and bedding, have been converted to an earthy-smelling material that looks like tiny black flecks of finely ground coffee. Applying vermicompost to the soil properly results in robust plants that grow quickly and produce sizable vegetables, fruits and flowers.
Most studies of vermicompost indicate its best to avoid using it to comprise 100 percent of the growing medium and instead mix it into garden soil or potting mix so it comprises about 20 percent of the volume. Photos of carrots and marigolds grown in a field trial conducted by Washington State University show that plants grown from seed in a mix of 20 percent vermicompost grow bigger and taller than those grown in mixes with no vermicompost or mixes with a smaller proportion of this soil amendment.
You can add worm manure to seed flats, pots and window boxes in the recommended 20 percent ratio. You can also add ½ to 1 inch of vermicompost directly to the top of garden soil, optionally mixing it with the top 4 inches, Purdue University Extension recommends. Or add ½ inch to the top of your lawn. Place 1 inch in a ring around tree trunks. Commercial farmers with access to large quantities of vermicompost, especially those who prepare it onsite using optimal animal waste such as cow or rabbit manure, can apply a ton of vermicompost per acre.
Ideally start your worm bin early in the year so that the three-month cycle providing your first significant quantity of vermicompost becomes available slightly before the first frost-free date in your area. If you have a small worm bin, you may want to focus on providing the completed compost first to nutrition hogs such as tomatoes, which will benefit from the elevated but gentle levels of nitrogen and minerals in the vermicompost. Place a trowel full of worm compost in the hole receiving the transplanted tomato or apply it 1 inch deep around the base of the plant.
As you obtain additional cycles of worm compost from renewing the bedding and scraps in your worm bin after the first harvest, apply these as a top dressing for a midseason pick-me-up for outdoor plantings, recommends Mary Appelhof, author of "Worms Eat My Garbage."
Vermicompost added to seed-starting mix renders the mix unsterile and typically adds random seeds to the equation, especially if you've composted--for example--tomatoes, pumpkins, cantaloupe, melon and peppers in your worm bin and their seeds sprout. You can pull up the volunteer sprouts that compete with the deliberately planted seeds. It may be best for seeds susceptible to molds, such as bell peppers, to be started in a sterile mix and add vermicompost only at a later stage, when they are transplanted to peat pots as they get bigger.