Worm casts only need to be used sparingly because they are 5 times richer in available nitrogen, they have 7 times more phosphates and 11 times more potash than the upper 6 inches of topsoil.
Worm casts have much higher numbers of beneficial micro-organisms and a greater diversity and different spectrum of microbial species. This is why they not only improve soil fertility, they also help suppress plant diseases and help to suppress pests.
Because worm casts are so fine they will improve the water holding capacity of the soil, improve aeration and make it easier for plant roots to grow.
Using worm casts
You can sprinkle worm casts along the bottom of your seed row or throw a handful intot he hole at the time of transplanting - you only need to use about a handful per square metre.
Worm casts can be mixed with coir and sand to make a multi purpose compost. Mix 1 part worm casts with 4 parts coir and 1 part sand.
To make a concentrated worm tea, a 100% organic plant food, add 5 litres of water to 1 litre of worm casts, stir it well, decant the liquid and apply directly to plants.
Worm casts and disease suppression:
Most of the work on disease suppression has been undertaken by Professor Clive Edwards and his team at the University of Ohio. He proved the microbial power of vermicompost to suppress plant diseases by showing that the suppressiveness was lost when the vermicompost was sterilised.
Plant diseases suppressed by vermicompost:
Soil borne diseases: Pythium, Rhizoctonia, Fusarium, Schlerotinia, Club root Plasmodiophora brassicae, Verticillium wilt, Phytophthora, Phomopsis
Foliar diseases: Botrytis, Powdery mildew, Plectosporium blight, Septoria lycopersici ( tomato leaf spot ), Alternaria solani ( early blight )
Worm Casts and pest suppression:
Prof Edwards team at Ohio State University carried out extensive glasshouse experiments on the effects of vermicompost mixes on populations of economically important pests. A range of plant crops were grown in mixes of standard potting compost and vermicompost. Infestations of two-spotted spider mites, aphids and mealy bugs were introduced. Damage and population numbers were assessed over a number of weeks and additional observations were made with cabbage white butterfly caterpillar damage and cucumber beetle.
The results showed a significant decrease in the damage caused by the pests.