Abstract: The types of flower2bud differentiation in 135 cultivars of tree peonies ( Paeo2
nia suffru ticosa) were identified and grouped as few (3 - 4) , medium (5 - 7) or many (8 -
10) in number of flower-buds and small, medium or large in flower2bud differentiation gradi
ent. Ten rep resentative cultivars were chosen and investigated for their behavior in forcing suc
cessive secondary flowering. The results indicated that the flower2bud number and differentia
tion gradient were directly related with secondary flowering. The cultivars with fewer flower-
buds and large differentiation gradient could not be forced for successive secondary flowering in
the same p lant, while the cultivars with medium2numbered ormany flower2buds and small dif
ferentiation gradient flowered successively from January to Ap ril 2006 in the same p lant by forc
ing. Among the latter, Paeonia‘Ru Hua Si Yu’had a secondary flowering percentage of 75%
and p roduced good quality flowers during the p rimary and secondary flowering.

Key words: Paeonia suffruticosa, Flower-bud differentiation, Successive secondary flowering