Lantana Cultivars Respond Differently to Plant Growth Regulator Substrate Drenches

One of the best-performing herbaceous annual bedding plant for landscapes and containers is lantana (Lantana camara). Lantana cultivars provide color throughout the summer, even in hot and dry conditions. However, controlling the size of lantana produced in containers can be a challenge. Our objectives were to quantify the efficacy of substrate drenches containing plant growth retardants (PGRs) on growth of lantana cultivars varying in growth habit. ‘Little Lucky Peach Glow’, ‘Lucky Peach’, and ‘Landmark Peach Sunrise’ lantana cuttings were individually planted into 4.5-inch diameter round containers filled with a commercial, soilless growing substrate comprised of sphagnum peat moss and perlite. Fourteen days after planting, once the roots of lantana cuttings reached the container wall, 70-mL aliquots of solution containing 0 (control), 0.5, 1.0, 2.0, or 4.0 ppm ancymidol, flurprimidol, paclobutrazol, or uniconazole were applied to the surface of the growing substrate. Six weeks after applying PGR drenches, data were collected. The plant height from the surface of the growing substrate to the top of the plant canopy and the widths at the widest point of the plant and perpendicular from that widest point were recorded. The Growth Index (GI), an integrated measurement of plant size incorporating the height and widths of plants, was calculated. There was variation in plant height, width and GI among the cultivars used in this study. ‘Little Lucky Peach Glow’, ‘Lucky Peach’, and ‘Landmark Peach Sunrise’ are representative cultivars of small-, moderate- and large-growing series and the height, width, and GI of plants not treated with any active ingredient reflected this. In addition to the differences among lantana cultivars, we found variation in activity among the different PGRs applied. Ancymidol generally had the lowest activity across the four PGRs applied. For example, drenches containing 4.0 ppm ancymidol resulted in plants that were similar to plants treated with 0.5 to 1.0 ppm flurprimidol or uniconazole or 2.0 ppm paclobutrazol for ‘Lucky Peach’ lantana. Across all cultivars, flurprimidol and uniconazole had the greatest activity in suppressing plant height, width, and GI. Substrate drenches containing flurprimidol, paclobutrazol, or uniconazole are useful to control size of lantana produced in containers, though the recommended concentration depends on the active ingredient and the growth habit of cultivars being treated.