A study of the effects of pruning and deheading on the flowering behaviour of Leucospermum cv. Scarlet Ribbon and Leucospermum Saxosum

Abstract

Leucospermum plants have a relatively short flowering period and peak flowering periods often coincide with low prices on the export market. Two field trials were therefore carried out at Pinfields farm Ruwa, Zimbabwe from 2002 to 2004 to investigate the effect of two cultural practices, pruning and deheading, on the flowering behaviour of two Leucospermum cultivars: Scarlet Ribbon and Saxosum. The first trial investigated the effect of pruning and deheading two different aged plants (2½-3years ‘old’ and 1-1½ ‘young’) of Scarlet Ribbon. The second experiment compared the response to pruning and deheading of two cultivars, Scarlet Ribbon and Saxosum, on flowering time. Measurements taken in all experiments included the period from pruning to harvesting, the extension to harvest time after deheading of the primary inflorescence, length of harvested flowering stems, inflorescence diameter of harvested flowering stems, grading of stems and losses in harvest due to pruning and deheading. Pruning of plants was carried out at different times from January to July, including the control treatment (normal farmer practice) for both experiments. Deheading of the primary inflorescence bud was at 0-5 mm, 6-10 mm, and 15-20 mm and was compared with a control (disbudding all but the primary bud). Pruning and deheading treatments significantly (P<0.05) extended harvest time for all the experiments. The extension to harvest varied with pruning time, deheading diameter, age of plants and cultivar. Pruning early (Jan/Feb) and deheading early in the induced reproductive phase resulted in a longer extension to harvest time compared to late pruning (May/Jun and Jun/July). Old plants had a shorter extension to harvest time compared to young plants. Harvesting of flowering stems post pruning was earlier for old plants by 2 weeks compared to young plants of Scarlet Ribbon. The significant (P<0.05) age x deheading diameter interaction resulted in long stems for old plants for all the deheading diameter treatments. Quality and quantity of stems and earnings from old plants were higher than for young plants. Pruning and deheading old plants of Scarlet Ribbon resulted in the least losses (10%) with regards to harvested stems compared to young plants (12.5%). Results indicate the ability of old plants with more plant matter to effectively resume growth and development to the flowering stage due to more assimilates facilitating this compared to young plants. When the two cultivars were compared, Scarlet Ribbon had a longer extension to harvest time than Saxosum. The result was similar when comparing the extension to harvest after deheading. The effects of pruning and deheading are cultivar specific as was demonstrated in this study. Although in Zimbabwe both Scarlet Ribbon and Saxosum are regarded as early flowering in the industry, Saxosum was harvested much earlier by 2.4 weeks than Scarlet Ribbon. Flowering and harvest period for Saxosum was shorter (5 months) compared to Scarlet Ribbon (7 months). In addition, a difference in flower head complexity resulted in early flowering for Saxosum. Saxosum is naturally multiheaded thus exerting less apical dominance through correlative inhibition of the secondary bud. The secondary bud resumed growth and flowered earlier than Scarlet Ribbon, which produces solitary inflorescence naturally. Scarlet Ribbon produced longer stems than Saxosum. The significant (P<0.05) cultivar x pruning time interaction showed a reduction in stem length for Saxosum. There was no significant difference to the inflorescence diameter of harvested stems for both cultivars. Losses in harvest were high for Saxosum (16.7%) than for Scarlet Ribbon (12.5%) when the plants were deheaded at 6-10 mm. Deheading late in the season from late July to September at a diameter of 15-20 mm produced the highest losses. Deheading resulted in different quality stems for the two cultivars however, the stems were of marketable quality. Scarlet Ribbon produced more flowering stems of higher quality and correspondingly high earnings compared to Saxosum. Scarlet Ribbon had the most favourable response to pruning and deheading on flowering time compared to Saxosum. It is therefore recommended that pruning be done early (Jan/Feb and Mar/Apr) and deheading at 0-20 mm diameters up to mid July as harvest period can be extended up to November for iv Scarlet Ribbon with good quality stems, earnings and minimal losses in the Ruwa farming area. Old plants respond better to pruning and deheading than young plants.