PLANTS FOB OUTSIDE PLANTING 431 



those countries. Native species are single, the double 

 forms being the result of cultivation. 



723. Commercial importance. The dahlia is quite 

 an important commercial flower. The grower's revenue, 

 however, comes more largely from the sale of tubers in 

 the spring, than from the sale of cut-flowers. Dahlias 

 have a tendency to produce foliage and wood, rather than 

 flowers, and in the early stages of its cultivation it was 

 difficult to get the plants to bloom at all in the northern 

 part of the United States. Breeders have, however, 

 developed a race with early-flowering characters. The 

 show type will usually bloom in ten weeks from the time 

 of planting, and some in even less. The first improvement 

 in dahlia culture was in getting double forms; next, 

 colors were improved, and the stems on individual flowers 

 were lengthened and made stronger. 



724. Propagation. Dahlias may be propagated from 

 cuttings or from seed. The clumps are potted in Feb- 

 ruary. When the shoots have made the third or fourth 

 pair of leaves, the cuttings are made and inserted in sand. 

 The cut should be made through the node, and the cut- 

 tings kept in a temperature of about 55 to 60, while 

 the temperature of the sand is usually from five to ten 

 degrees higher. As soon as the roots are well started, the 

 cuttings may be potted. Young plants should be kept 

 close to the glass, to prevent spindling. Dahlia seed sown 

 in March has given the most satisfactory results. 



725. Culture. Select a rich, deep soil of medium tex- 

 ture and well drained. Heavy clay soils should be avoided. 

 The soil should be plowed or spaded to a depth of fourteen 

 or eighteen inches to make it fine and mellow. Lay the 

 tubers flat, planting them from six to eight inches deep. 



Cactus, decorative, show, fancy, single and collarette 



