Growth Regulation of Mexican Sage and ‘Homestead Purple’ Verbena During Greenhouse and Nursery Production

Abstract

Abstract Salvia leucantha (Mexican sage) and Verbena canadensis ‘Homestead Purple’ were treated with the plant growth retardants (PGRs), Cutless, Sumagic, B-Nine/Cycocel tank mixes, or Pistill under both greenhouse and nursery conditions. Increasing rates of all PGRs applied to both species reduced plant size in the greenhouse for 6 weeks after treatment (WAT). Growth reduction of Mexican sage with the most effective rate (providing greatest growth control) of each PGR over this period averaged 11% with Cutless, 15% with Sumagic, 23% with B-Nine/Cycocel tank mixes, and 25% with Pistill. For verbena, size control with the most effective rate of each PGR averaged 15% with Cutless, 18% with Sumagic, 27% with B-Nine/Cycocel tank mixes, and 29% with Pistill. After transplanting greenhouse-grown plants into outdoor ground beds, only Mexican sage treated with B-Nine/Cycocel were significantly smaller 4 weeks after planting (WAP). Greenhouse-grown verbena treated with Sumagic, B-Nine/Cycocel tank mixes, and Pistill and planted in the landscape were 15—23%, 18–25%, and 0–20% smaller, respectively, than control plants at 2 WAP, but by 4 WAP, all PGR-treated verbena were similar in size to control plants. Under nursery conditions, Cutless and B-Nine/Cycocel tank mix reduced Mexican sage size up to 4 WAT. None of the PGRs affected plant size at 6 WAT. The most effective rate of each PGR (averaged over the duration that a PGR was significant) suppressed shoot growth 16% for Cutless, 12% with Sumagic, 20% for B-Nine/Cycocel tank mixes, and 29% for Pistill. For verbena only, Sumagic suppressed growth up to 10% at 2 WAT, and no PGR effectively controlled growth under nursery conditions 4 WAT.