The practice of removing an herbaceous plant’s growing point (commonly termed pinching or topping) has been used for many centuries to affect growth, plant productivity, or shape (Escher, 1996; Hunt, 1893). Most commonly, pinching is used to reduce plant height and encourage branching (Faust, 2006). When used on cut flower species that typically only produce a single flower, pinching during the early vegetative stage, allows a multibranched plant to develop (Badge et al., 2014; Cheong et al., 2002; De Pascale et al., 2005).
Pinching has been practiced on many annual species used as cut flowers, including gypsophila [Gypsophila paniculata (Cheong et al., 2002)], lisianthus [Eustoma grandiflorum (De Pascale et al., 2005)], and african marigold [Tagetes erecta (Badge et al., 2014)]. In herbaceous perennials such as delphinium (Delphinium elatum) pinching of early shoots breaks apical dominance to encourage growth of secondary shoots (Garner et al., 1997). Although pinching of sunflowers is apparently widely practiced (Armitage and Laushman, 2003; Dole and Wilkins, 2005), scientific study of this topic has been limited. A 1-year study in Mississippi determined that pinching increased yield of branching more than nonbranching cultivars, but did not manipulate spacing nor include a nonpinched control treatment (Sloan and Harkness, 2010). The research presented here documents the effects of pinching and plant spacing on productivity and cut flower characteristics of two unbranched cultivars of sunflower.
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