BBC Gardeners' World presenter Joe Swift has shared three simple steps to achieve perfect container-grown shrubs. Writing in the Radio Times, Swift warned that shrubs left in pots for too long can become 'pot-bound', where roots fill the container, preventing the plant from retaining moisture and nutrients.
Swift recommends repotting shrubs every few years, but advises against moving them into a significantly larger pot. He suggests going up just one size, allowing 2.5cm to 5cm of space around the root ball. This prevents the plant from rocking in loose soil, which can create air gaps or lead to waterlogging or dryness.
For the potting mix, Swift advises using a soil-based compost like John Innes No 3, or a homemade mix of two parts garden soil and one part sieved garden compost. He also recommends adding a slow-release fertiliser such as blood, fish and bone, and placing a 2.5cm layer of crocks over drainage holes. After repotting, the shrub should be watered thoroughly.
For shrubs that become too large to repot, Swift suggests controlling size by pruning both top growth and roots. Remove the plant from its pot, scrape away some compost to expose roots, prune weak or damaged roots, and trim top growth before repotting in the same container.
