Roses and hydrangeas can be protected from black spot and fungal leaf spot using a simple, natural soil amendment, according to a gardening expert. The method involves applying horticultural cornmeal around the base of the plants, avoiding the need for harsh chemical sprays.
Fungal Disease Threat to Popular Garden Plants
Fungal infections are the most common and severe ailment affecting both roses and hydrangeas. Roses are highly vulnerable to black spot, caused by the fungus Diplocarpon rosae, which attacks leaves, producing purple or black markings and often causing them to drop early. Hydrangeas are susceptible to fungal leaf spot, which appears as pale brown markings with a darker brown edge. As the condition progresses, markings expand, foliage turns yellow, and leaves ultimately fall away.
Expert's Organic Solution
Gardening expert Caroline, who posted on her Facebook page Figement Cottage Gardens, revealed how to "save your hydrangeas and roses from black spot the organic way." She stated that "all it takes is horticultural cornmeal." Caroline explained: "You want to use horticultural cornmeal versus corn starch, cooking cornmeal, or corn gluten, because it's milled from the outer shell of the kernel and contains more protein that feeds the beneficial fungi that outcompetes black spot."
Application and Benefits
To apply, distribute one cup of cornmeal to each shrub. One bag typically contains enough for 16 cups or 16 large roses or hydrangeas. Smaller shrubs require only a quarter to half a cup. Scatter the cornmeal around the base and work it into the earth. Caroline noted: "I did this before a big rainstorm to water it in."
Farmers use cornmeal for many purposes, including fertiliser, weed management, soil conditioner, and an organic fungicide. The gardener says it eliminates the need to spray roses and hydrangeas with copper fungicides to combat and ward off black spot. Instead, helpful fungi develop on the cornmeal and outcompete the black spot spores. She said: "Rose gardeners swear by it."
Ongoing Control Measures
After addressing black spot and leaf spot, it is essential to take measures to keep them under control. Mulching can help by nourishing the soil and roots, while also covering black spot and other fungal disease spores, making them less likely to be splashed upwards in rainfall to re-infect a treated plant.
