CASTINGS CALL: We call for your observations about the effect of earthworm castings on plant pest resistance.

It’s well known that worm castings are an excellent organic soil amendment, are rich in beneficial microorganisms, improve the structure and texture of soils and increase the availability of nutrients. Less well known is that plants growing in soil amended with worm castings have shown increased resistance to various insect pests, including mealybugs, scale and aphids.

The connection between worm castings and increased insect pest resistance is reported in an article appearing in the December, 2003 issue of The Fruit Gardener, the journal of the California Rare Fruit Growers. The author, George Hahn, claims that in controlled experiments, the use of worm castings boosted dramatically the resistance of plants to various sucking insects—aphids, mealybugs, whiteflies, scale, etc.

Informal tests by members of our own staff also strongly suggest that worm castings improve insect pest resistance. Last November, we mixed worm castings and potting soil to repot some asters infested with root mealybugs. Two months later, the root mealybugs had completely disappeared. Also, we top-dressed the soil at the base of a grapefruit tree badly infested with citrus thrips and cottony cushion scale and found that the tree was completely free of these insects and showed healthy, clean foliage after six weeks.

We are very interested in any stories our customers may have about their experience with worm castings and insect pest or disease resistance. Please email or call if you have any anecdotes to share!

–Margaret