Family: Asteraceae

This genus was discovered in the mountains of Mexico by a Spanish physician in the 17th cen­tury. In the 20th century many flower forms were developed and cultivars produced. Today it is possible to choose from decorative, cactus, pompon, paeony-flowered, waterlily, single and collarette dahlias. Dahlias therefore come in many different flower forms and in every imag­inable colour. Flower sizes range from tiny pom­pons at less than 5 cm (2 in) across, to very large blooms, 30 cm (12 in) or more wide, and they may be single, double or semi-double. Dahlia plants grow from 30 cm (12 in) to nearly 2 m (6 ft) high, while the tree dahlia can reach 5 m (16 ft) in height. Shrubby dahlias have a very long flowering period from early summer until late autumn and make first-class cut flowers. Tree dahlias flower from middle to late autumn.

Varieties

A wide range of varieties is available from specialist growers whose details are in gar­dening magazines. Most garden centers carry a small range in spring.

Cultivation

Dahlias like rich, well-drained soil, heavily enriched with manure or compost, as they are heavy feeders. They need full sun all day, with protection from strong wind. Plant dormant tubers in mid-spring, 10-15 cm (4-6 in) deep, with the neck containing the dormant buds pointing up. Spacing between plants depends on the variety. Small growers should be set 30 cm (12 in) apart, while very large growers should be 75-100 cm (30-40 in) apart. Stakes and labels should be put in at planting time to avoid damaging the tubers later. Water well after planting the tubers, but further water­ing is usually unnecessary until after growth begins. An alternative technique is to start dor­mant dahlia tubers into growth in early spring in a heated greenhouse, in boxes of moist peat, and to take basal cuttings when the shoots are about 5 cm (2 in) high. Root them with bottom heat, pot up rooted cuttings individually, and plant out the young plants when frosts are over. Bedding dahlias are raised from seed sown in
early spring under glass. Again they are planted out when frosts are over. Once flowering has begun, feed dahlias monthly with blood, fish and bone, or with complete plant food. A mulch of decayed animal manure will provide extra nutrients for the plants and will also help to retain soil moisture. During growing and flowering, give deep, weekly waterings. Cut flowers or dead-head regularly to prolong blooming. Tree dahlias are unsuitable for cut­ting. Snails love dahlia foliage and flowers so take care to control them. In frost-prone cli­mates, autumn frosts will kill off the top growth. At this stage, lift the tubers, dry them off and store in a cool, frost-free place for the winter. Bedding dahlias are discarded at the end of the season.

Climate

Zone 10.