Natural remedy for common fungal diseases

A gardening expert has shared a simple, chemical-free method to protect roses and hydrangeas from black spot and fungal leaf spot. The advice, posted on the Facebook page Figement Cottage Gardens, recommends using horticultural cornmeal to fight the fungal conditions that commonly affect these plants.

Black spot in roses is caused by the fungus Diplocarpon rosae, which attacks foliage and creates purple or black markings, often causing leaves to drop early. Hydrangeas are susceptible to fungal leaf spot, which appears as pale brown markings with darker brown edges, and can cause leaves to yellow and fall as the condition progresses.

The expert, identified as Caroline, described the method as a way to "save your hydrangeas and roses from black spot the organic way." In her post, she said "all it takes is horticultural cornmeal," explaining that gardeners should use this specific type rather than corn starch, cooking cornmeal, or corn gluten because it is milled from the outer shell of the kernel and contains more protein that feeds beneficial fungi.

How to apply the cornmeal

For application, Caroline recommends using one cup of cornmeal per large shrub, and a quarter to half a cup for smaller shrubs. A single bag of cornmeal generally provides enough coverage for 16 cups, or enough for 16 substantial roses or hydrangeas.

The cornmeal should be scattered around the plant's base and worked into the earth. Caroline noted that she applied it before a big rainstorm to water it in.

This method works by encouraging beneficial fungi that develop on the cornmeal and outcompete the black spot spores, according to the expert. She added that "Rose gardeners swear by it."

Additional benefits and context

Cornmeal is used by agricultural professionals for a variety of purposes, including as a fertiliser, for weed suppression, soil conditioning, and as an organic fungicide. The gardening expert suggested that this approach eliminates the need for spraying roses and hydrangeas with copper fungicides to address and ward off black spot.

Mulching can also be effective in preventing the return of black spot and leaf spot by covering the spores and reducing splashing during rainfall.

Both the Daily Express and the Liverpool Echo reported on Caroline's advice, presenting the tips as a natural, chemical-free way to protect plants.