The perennial growth habit of castor plants (Ricinus communis L.) limits mechanical harvest because the plant grows very tall when the environmental conditions are favorable and produces many immature fruits, fresh stems, and green leaves at harvest time. There is a demand for chemicals that prevent excessive growth and defoliate the plant to prepare the crop to be harvested. This study had the objective of evaluating two growth retardants and three harvest aids (desiccants and defoliants) applied on castor crop at different times and doses. The experiments were conducted in Lubbock, TX, USA from 2007 to 2010. The growth retardants were Pix® (mepiquat chloride) and Stance® (mepiquat chloride+cyclanilide) applied one time at five development stages. The harvest aids were ET® (pyraflufen), Ginstar® (thidiazuron+diuron)+Finish® (etephon+cyclanilide), and paraquat. The growth retardant Pix® promoted rather than inhibited the vertical growth of castor plants, but in general, this product did not influence the seed yield. Stance® did not influence vertical growth, but increased doses were associated with higher castor seed yields. The effect of Stance® on seed yield was more intensive when applied from the 8th node stage through the first expanded leaf after the primary inflorescence. Early termination caused seed yield reduction compared with frost-killed plants, but the loss was progressively diminished as the termination occurred later in the season. There were differences in the effect of harvest aids. The reduction of mean seed yield caused by paraquat was not significant, but ET® and Ginstar®+Finish® reduced the mean seed yield compared with untreated plants.