The experiment reported in this paper was carried out to determine the most appropriate time to root cuttings of six of the most common rootstock varieties of grapes under field conditions in the state of São Paulo. The rootstocks tested were Rupestris du Lot, Riparia x Rupestris 101-14, Golia, Kobber 5BB, Mourvedre x Rupestris 1202, and Aramon x Rupestris Ganzin No. 1. The following rooting dates were compared: mid of May, June, July, August, September, and October. Cutting of all varieties tested gave good rootstocks when rooted in June, July, and August. Not only was the percentage of established rootstocks higher, but there was also a higher percentage of vigorously growing plants. Cuttings rooted in May, September, and October gave poor results. The good results obtained in June, July, and August were attributed in great part to the use of cuttings from completely lignified branches that had dormant buds, whereas those used in May were taken from branches still immature, and those for September and October, from matrices that were starting the new vegetative growth.