Harvest Season and Fertilizer Effects on Seed Production of Leavenworth's Coreopsis

Abstract

Effects of season and fertilization on seed production were investigated for a central Florida ecotype of Leavenworth's coreopsis ( Coreopsis leavenworthii Torr. & A. Gray) grown in containers. Since container-grown ecotypes of native, herbaceous species are frequently grown using nutrient regimes lower than those for production of typical garden plants, Osmocote 18N–2.6P–10K (18–6–12;8–9 month formulation) was incorporated into the soilless substrate at one-half the low, low, and medium label rates for container-grown herbaceous plants [1.8, 3.6, and 5.4 kg/m 3 (3.0, 6.0, and 9.0 lb/yd 3 ], respectively. Seed were harvested from mature heads (capitulescences) in late May to mid-July, and then again from late July to late October after plants had been cut back and reflowered. Seed yield and quality were greatest for the May–July harvest. Averaged over fertilizer rate, there were 3-fold more filled seed per mature head for the May–July harvest than during July–October. Mature head production was most responsive to increases in fertilizer rate during May–July. Percent germination of viable seed was nearly 90% or more for both harvests, but there were more viable seed for May–July than for July–October (75 vs. 57%). Seed also ripened much more uniformly during May–July then during July–October. Based on these conditions and results, the best time to harvest seed was from May to early July.