Worm castings provide numerous benefits when used outdoors. The organic matter found in the castings helps to improve soil structure, allowing for better aeration and drainage. This can help to reduce compaction and increase moisture retention, which is especially important during periods of drought or extreme heat. Worm castings also act as a natural fertilizer, providing plants with essential nutrients such as nitrogen, potassium and phosphorus that are necessary for healthy growth. Worm castings contain beneficial microbes that can help to break down organic material into usable forms of plant nutrition. These microbial populations can also aid in disease prevention by helping to suppress pathogens in the soil. Worm castings have been shown to reduce water runoff from gardens while still maintaining high levels of moisture in the soil profile.