The effects of clipping and daylength treatments and their carryover effects on the clonal growth of the perennial grass Holcus lanatus L. were investigated. Plants from ten clones were grown in six combinations of two daylength and three clipping treatments. Both clipping and low daylength reduced the tillering rate of all the clones but the clones differed in their degree of response to these treatments. After eight weeks, the treatments were discontinued and plants were grown in a common environment for seven weeks. Four-week-old tillers from the plants were repotted and grown in a common environment to examine the possibility of ‘carryover’ effects of the parental environments. After 8 wk of growth, there were main and interaction carryover effects of daylength and clipping on the tillering rates, biomass and tiller extension rates of the plants, which, however, differed greatly among clones. These differences among clones in both direct and carryover treatment effects, on clonal growth, indicate how the effects of many different environmental variables may interact to produce an environment that is highly heterogeneous in space and time, influencing the coexistence of genotypes and species.