Worm Castings is worm poo harvested from worm farms. More than a fertiliser, it is packed full of beneficial microbes which help plants access nutrients, and it improves the soil by increasing soil biology and helping with moisture retention.
Castings are often added to seed raising or potting mix, or use a small amount in planting holes when planting out. The castings can also be steeped in liquid (approx. one cup per bucketful). Leave for a day or two, stirring ocasionally and use the resulting liquid 'worm juice' as a safe, liquid plant tonic.
Worm juice and castings improve the health and vigor of plants, which in turn means less insect and disease attack.