Many gardeners make the mistake of treating all herbs the same when it comes to fertilising. While leafy herbs like basil, mint, or parsley benefit from feeding in summer to produce more flavoursome leaves, woody herbs such as lavender and rosemary originate from arid climates and perform better in nutrient-poor soil.
Why fertiliser harms lavender and rosemary
Feeding Mediterranean herbs in late July or early August can cause their flowers or leaves to drop and encourage soft, leggy stems that attract pests like slugs. The stress from fertiliser also weakens the plants, making them less likely to survive autumn, as their stems become vulnerable to cold damage.
The simple gravel solution
Amanda MacArthur, an expert from the Food Gardening Network, recommends adding gravel to the soil around lavender and rosemary during summer. She said: "This may not be the first thing you think of as mulch, but herbs like rosemary that come from Mediterranean climates love the drainage and the heat that gravel offers. And since gravel isn't going to decompose, it's a good choice if your herb garden is also part of your landscape design."
Benefits of gravel mulch
Mulching typically involves using bark to retain moisture, but lavender and rosemary are susceptible to root rot and fungal conditions in waterlogged soil. Gravel improves drainage and reflects sunlight, warming the soil to replicate the dry, stony conditions these herbs prefer. This promotes stronger roots, sturdier foliage, and better flower production. It also enhances essential oil levels, making lavender more aromatic and rosemary leaves more intensely flavoured.
Whether grown in pots or in the garden, adding a modest amount of gravel can help lavender and rosemary flourish throughout the summer months.
