Establishment success and relative costs of four annual species for roadside planting

Abstract

Seeds of Celosia argentea L. 'Pampas Plumes', Cosmos sulphureus Cav., Helianthus annuus L. '7111', and Zinnia elegans Jacq. 'Gold Medal Mixture' were mixed with clean sand and hand-broadcasted over 60-ft2 (6.7-m2) plots at rates of 4 or 8 oz/1000 ft2 (122 or 244 g/100m2). Each plot was either left undisturbed after sowing or the seed was raked into the soil surface. Estimated costs were calculated using the approximate number of seeds planted per plot and the cost per seed versus the number of plants reaching anthesis. Celosia and Zinnia bloomed for 42 days, Cosmos sulphureus for 28 days, and Helianthus for 12 days. Seeding rate had little effect on the number of plants maturing to flower in all species except Cosmos. There were no significant differences in number of weeds between treatments for any of the species. Raking the seed into the soil significantly improved germination at 2.5 and 5 weeks for Celosia, Cosmos, and Helianthus, but not for Zinnia. In Celosia, raking the seed into the soil more than doubled the number of plants maturing to flower, while in Cosmos the number reaching anthesis was not significantly altered by raking. The lowest costs per flowering plant occurred when the seed was raked into the soil for Celosia, Helianthus, and Zinnia.