At the first blink of warmth, my beautiful acanthus is covered in mouldy white spots (black underneath) that kill the leaves, attracting snails, which then eat the few surviving leaves. Should I admit defeat?
Powdery mildew is a natural part of gardening – it happens to a wide variety of plants. The simplest solution is a shedload of muck. Your acanthus (aka bear’s breeches) is too dry and there’s not enough air circulation around the plant, which is making perfect conditions for powdery mildew. Add a lot more mulch around the base of the plants – go crazy with leaf mould or homemade compost, and thin out the plants so that the air can move more freely. Remove infected leaves immediately; if you allow them to decompose into the soil there will be more spores the following spring.
If you’ve chosen a spot where you can’t thin out the plants or increase air circulation, consider trying something else that will cope with these conditions. Our native shield fern (Polystichum aculeatum) will cope, as will P. setiferum ‘Herrenhausen’, an elegant, finely divided, soft-shield fern. Both are a similar size to your acanthus.
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