Rosemary Cultivar Ontogeny Affects Success as Potted Christmas Tree Shaped Topiary

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  • 1 University of Illinois, Department of Natural Resources and Environmental Sciences, 1201 South Dorner Drive, Urbana, IL 61801

Greenhouse production of rosemary (Rosmarinus officinalis L.) as small potted Christmas tree topiaries for holiday sales has become necessary for many companies marketing to large retail outlets. Topiaries must be sheared multiple times to obtain an acceptable Christmas tree shape. Cultivars vary in physical attributes, suggesting that they may respond differentially to mechanical shearing during production. This study assessed sixteen rosemary cultivars for their potential as potted Christmas tree shaped topiaries. Beginning July 2001, rosemary plants derived from vegetative propagation of shoot tips were provided high fertility and maximum light in a greenhouse. From August to October, plants were pruned monthly for a total of three shearing events. The crop was considered mature on the targeted market date of 5 Dec. Final plant quality was visually assessed using a 1 to 5 scale that accounted for taper, plant-to-pot ratio, canopy density, foliage quality, and overall appeal, with one point being removed for each factor not meeting industry expectations. The cultivars varied in their performance as Christmas tree shaped topiaries with most being unacceptable due to minimal basal branching or excessive leaf burn that negatively impacted shape, taper, and aesthetics. Six of the cultivars, `Taylor's Blue', `Herb Cottage', `Joyce DeBaggio' (Golden Rain), `Shady Acres', `Rexford' (Rex), and an unnamed clone, were suitable for commercial use having visual ratings ranging from 3.8 to 4.5. These cultivars had equally healthy foliage with little damage. `Taylor's Blue', `Shady Acres', `Joyce DeBaggio' (Golden Rain), the unnamed clone, and `Herb Cottage' had foliar damage ratings ranging from 3.3 to 3.8 and were not significantly different from the most healthy cultivars, `Logee White' (Thinleaf White), `Salem', and `Hill Hardy', all of which had mean ratings of 4.0. These cultivars should be examined for additional attributes that may enhance their performance as Christmas tree shaped topiaries.

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