13.4.3  Ornamentals and nursery stock

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Commercial production of flowers with CO2 enrichment is frequently advantageous (see section 6.2.3 for related effects). Roses and chrysanthemums produce larger flowers and longer, stronger stems. High CO2 also reduces the number of stems which fail to flower, thereby increasing marketable yield. For geraniums and carnations, enhanced growth of lateral shoots at high CO2 concentrations increases flower yield, generally increases flower quality and promotes earlier flowering. Treatment of stock plants results in increased numbers of cuttings which are more vigorous, flower earlier and produce more flowers.

CO2 enrichment often results in more compact pot plants. This is a result of enhanced branching and may obviate ‘pinching’, a labour-intensive practice to produce bushier plants. Major advantages of CO2 enrichment for nurseries are reduced production time and increased throughput per year. Little research has been done on bedding plants, but flowers and foliage may be larger with a reduction in time taken for sale.

Plants with variegated foliage, because of their attractiveness, make up an important component of the nursery trade. Often a considerable proportion of leaf area has a reduced chlorophyll content and capacity for photosynthesis. The generally reduced vigour of these plants leads to a longer time to reach marketable size compared with completely green cultivars. Variegated cultivars of oleander and the Australian native plant, willow myrtle, both showed a greater growth response to CO2 enrichment compared to their fully green counter-parts. Enrichment thus offers nurseries a cultural approach for the production of slower growing, more highly valued variegated cultivars. It is also beneficial for accelerating the development of young trees such as citrus rootstocks and forest tree seedlings, thereby shortening holding time and reducing costs.