The Benefits of Compost Tea

Before you start worrying about the fungal diseases that affect many garden crops this time of year, consider brewing up a batch of fermented compost tea. It is cheap, easy to make, and can protect your plants as well as help them out if they’re already suffering. Compost tea has been studied around the world and has been found to reduce fungal diseases by 50 to 90 percent. What do I mean by fungal diseases? These are diseases spread by spores (like microscopic seeds that germinate on leaf surfaces) and are encouraged by warm, wet conditions. This is why plants that have smooth or waxy leaves are less likely to be infected than plants that have textured or hairy leaves (which hold water). Common fungal diseases include:

  • Powdery mildew (white spots on cucumbers and winter/summer squash)
  • Early blight (brown circular spots with concentric rings on tomato and potato)
  • Late blight (irregular brown to black spots with dark outlines and fuzzy undersides on tomato and potato in late July)
  • Septoria leaf spot (small dark brown spots sprinkled over yellowing leaves of tomato and potato)

While not fully understood, compost tea is believed to be beneficial for several reasons. Fermentation creates a healthy community of fungi and bacteria, which may outcompete fungal disease and help support a plant’s natural defenses.  It also contains nutrients, which can be absorbed through foliage.

To make compost tea, mix one part mature compost that contains manure with five parts water. Allow the mixture to sit in a shady place for two weeks (it may become smelly!) Filter out large particles through cheesecloth, then spray on tops and bottoms of leaves every two weeks. The mixture will help reduce spreading of spores by infected plants, and can prevent infection of healthy plants.

- Adapted from The Gardener’s Guide to Plant Diseases, by Barbara Pleasant