Q With just 15cm of soil on top of clay, what can I grow?
Samantha Cleary, by email
ABUNNY SAYS The real issue is whether rainwater hits the clay layer and stays there, or drains away. If it’s the former, I would put in some form of drainage, but I suspect it does drain, although somewhat slowly. As soon as you start planting, you’ll find that the plants’ roots will grow into the clay too and help to break it up. Many plants grow well in just 15cm of soil. I suggest starting with small plants in this situation – virtually just rooted cuttings at fairly close spacing. If you plant a large specimen, you’ll need to dig into the clay and you’re basically putting it in a sump – a clay-lined hole that will fill with water. Add a deep layer of garden compost before planting (and annually after) and feed plants with organic liquid feed. This way you will quickly increase your soil depth. Potatoes, brassicas and roses should thrive, but if you do what I say, you’ll soon be able to grow most things.