EFFECT OF PROPAGATION TREATMENT ON THE GROWTH AND FLOWERING OF POINSETTIA 'PAUL MIKKELSEN'
By saving time we also save expense. In this respect the value of reducing the propagating period cannot be overestimated. The same principles apply to plants grown from cuttings, although it is more difficult to regulate the growth of cuttings than that of seed plants. A cutting is physiologically older than a seedling, and the greater a plant's physiological age, the more complex its reaction to growing conditions. The rooting period of cuttings evidently weakens the cellular system's ability to maintain vital growth functions, In earlier experiments at this Institute we observed a distinct difference between Chrysanthemums rooted for 10 days and for 16 days. Cuttings of the variety Paradise were rooted in a sand medium for 10 or 16 days. They were selected according to the size of the roots and were frown under equal conditions. The length and weight of the plants from these cuttings were measured 7 weeks after panning. Plants rooted for 10 days were 20% longer and 27% heavier than those rooted for 16 days. The size of the roots had only a very slight effect on the subsequent growth of these plants (2). Apparently the efficiency of growth was more reduced in the plants rooted for 16 days than in those rooted for 10 days. This difference was not eliminated during the next seven weeks.
Most poinsettia varieties need a longer rooting period than chrysamthemums do (3). Thus it could be assumed that the growth of poinsettia cuttings would be considerably weakened during the rooting period. But ten years ago Teter and Payne (4) showed that factors other tahn speed of rooting influence poinsettia development. They found taht final plant quality was affected by the propagating medium used.
Experiments on rooting poinsettia cuttings in fertilized peat were started in 1967 to obtain vigorous plants. Fertilized millpeat in peat pots and Jiffy-7 peat pellets were used as propagation media. The subsequent development of cuttings rooted in these media was compared with the development of cuttings rooted in sand in flats and in sand in peat pots. Cuttings were allowed a rooting period of 24 days. After that they were panned in peat-filled plastic pots. Some of the plants were