Dahlias are relatively easy to grow. They can be purchased from January onwards and there is a large and diverse selection of varieties to choose from. They are best planted outside after the risk of frost has passed. Dahlias prefer a rich soil with good drainage and choose a spot with full sun (they originate from Mexico) although they will tolerate partial shade. If possible, try to work in a good amount of well rotted manure prior to planting.
They should be planted approximately 15cm deep and 60cm apart. Dahlias can be started off earlier by planting in containers. Plant in compost and place in a frost free greenhouse then plant out as normal.
As your Dahlias grow and get taller, they may need support to avoid wind damage; a 1.5m tall wooden stake or similar sized can should suffice. Feed regularly with a high potash feed to encourage flowering. Your Dahlias will start to flower from July right through until the first frosts of the autumn and you can help them with regular deadheading. Once flowering has finished, leave in the ground until frost blackens the foliage then cut the stems to approximately 15cm above ground level and gently lift the tubers from the soil. Clean these off and store upside down for a week to allow any excess moisture to drain off then place in a box of dry peat and store in a frost free place (garage or shed) until you are ready to plant them out again the following spring.