Gardening on Thin Limestone Soil
Four inches of topsoil over rubble is normal around Bath. Fighting it is expensive; planting for it is not.
Free-draining alkaline soil over limestone is the default across much of this area. It rules out a familiar list of plants and opens up a far more interesting one.
What Will Not Work, However Much You Water
Rhododendron, camellia, pieris, most acers and blueberries all need acidic soil and will yellow and sulk regardless of feeding. Ericaceous compost in a planting hole buys you about two seasons before roots reach the native soil.
What Thrives Instead
Almost the entire Mediterranean palette. Lavender, rosemary, cistus, phlomis, euphorbia, bearded iris and most ornamental grasses actively prefer sharp drainage and low fertility. Enriching this soil to grow moisture-lovers makes them soft and short-lived.
Improve With Grit, Not Only Compost
The instinct is to barrow in topsoil and compost. Compost improves moisture retention but breaks down and vanishes within a few years. On a slope, adding grit and planting into the existing profile lasts far longer than importing a layer that washes downhill.
Where Depth Genuinely Matters
Trees and hedging need a decent root run and it is worth excavating properly for them, breaking up compacted subsoil in the base of the pit. Border perennials suited to the conditions do not — plant them into what is there.
