Find a sunny spot in the border or position your pot in the sun. Add granular feed to the compost and, once you have planted your Dahlia, water regularly to establish. Make sure to direct your can or hose to the bottom of the plant and really soak it down to the roots. If your Dahlia has large flowers you may need to put stakes in the ground, one per stem and tie the stems to the posts to support the weight of the flower. As the flowers fade, cut back the stems to a leaf joint, as this will encourage the plant to keep producing new buds. At the end of the season you can leave the Dahlia tuber in the ground if they are planted in a very free draining position and you live in a warmer part of the UK. You will need to cover it with at least 6 inches of mulch, for example bark chippings. You can also dig the tuber up, shake off the excess soil and place it in a dark, dry and cool place for the winter. Surround it with dry material like sand and replant it in the ground once there is no risk of frost in the next spring.