Many of us are put off by the idea of manure and waste products in our garden, but sometimes these are the exact ingredients our plants are craving. We probably don't have room for a cow in our backyard just for the manure, but thankfully, there are smaller friends that do the job just as well. They may not be glamorous, but worm castings (aka worm poo) make for excellent organic fertilizer. Rich in nutrients, minerals, and nitrates, this plant food has all sorts of benefits for your garden, if used correctly.
As digested worm food that has been excreted, "castings" is a delicate term for worm poo. Many types of manure are used as fertilizer, but some are less gardener-friendly than others. Worm castings are especially effective in that this dirt-like waste product can be incorporated into the soil to add nutrition, or spread across the top layer as mulch to hold in moisture and protect your plants.
Given that their function in most ecosystems is to serve as nature's decomposers, it makes sense that worms would add so much value to the soil with their waste. As they feast on the dirt, they leave behind a muddy output that is packed with nutrients — phosphorus, potassium, nitrogen, calcium, iron, and zinc to name a few. Another benefit of worm castings as fertilizer: unlike some organic manures, they don't have an odor.
Many fertilizers can burn a plant if directly and excessively applied, but this is not the case with worm castings. Worm manure is gentler on plants than other soil enrichers; not only can it be applied directly to plants without harming them, but it can also be steeped in warm water for a drink that plants will love. Worm tea draws out nutrients from the castings, and the resulting "worm tea" is both packed with vitamins and minerals and easily processed by your plants.
Worm castings are so beneficial that some gardeners use them in place of compost. This is certainly possible, as they are highly nutrient-dense, but store-bought castings may vary in quality and are more expensive than compost — though both are free if you make your own. Most growers find it best to use their worm castings as a boost to their compost, incorporating it into the mix in 1/8 to 1/4-inch layers. After all, it would take a lot of tiny worms to make enough castings to fill your garden.
Worm castings don't just add nutrients; they improve upon soil aeration, too. The castings have a high concentration of spongy, carbon-based humus, which keeps soil crumbly and well-suited to air circulation. The result is that your plant's soil will have better drainage and moisture retention, keeping only the water plants need, and air to give the roots room to thrive.
As if the rich food source and aeration improvement weren't enough, worm castings will protect your plants from harmful critters, too. They increase the production of a soil enzyme that helps break down the exoskeletons of many pests. If they get into a garden guarded by worm castings, unwanted invaders such as aphids, spider mites, and whiteflies will want no part of your produce — and if they do, they'll pay for it.
Worm castings can protect your garden from disease as well as predators. That high humus content isn't just good for improving aeration; it also attaches to harmful fungi and bacteria that would infect your plants, keeping them from multiplying and taking out your crop. The humus in worm castings fixes to heavy metals, too, preventing these from contaminating your produce.
Because they're so nutrient-rich, you don't need many worm castings to achieve their desired effect. A little goes a long way with worm manure, as you'll only need 1/4 to 1/2 a cup for every 100 square feet in your garden. Be sure to apply some on the top layer after planting, and add more, or make a tea, when your plants start to bloom, to get the most out of their growth.
They're beneficial and odor-free, so there's no reason you can't add worm castings to your outdoor and indoor potted plants, too. The general rule of thumb is to add 1/4 cup of castings for every six inches of container diameter, replenishing about once a month. Just that much will give your flowers and produce what they need to thrive!
Worm castings are wonderful organic fertilizers, and they may not burn your plants, but an excess can still cause problems. When applying, incorporate them evenly throughout your soil, and avoid placing an entire packed layer in the dirt. So much in one place may make it difficult for your plants to push through and root as they need, and you may end up doing more harm than good. Instead, mix the compost evenly into your soil, in a single top layer as mulch, or as a bottom layer to give your plants something to reach for.