The aim of this research was to characterise samples of yard trimmings (YT) and recirculated yard trimmings (RYT) that are used to co-compost organic fraction of municipal solid waste (OFMSW) taken from 18 composting facilities in Catalonia (NE Spain), to determine their contribution in the composting process, and to highlight the advantages and disadvantages of reusing RYT. We found significant differences between the characteristics of the two materials. RYT had higher pH levels, electrical conductivity, and organic and ammonium nitrogen content than YT. Nutrient content also shows an increment from YT to RYT, and in the case of P and K, this variation can be attributed to an exogenous source rather than the relative concentration during the composting process. We also found significant differences in particle size distribution and bulk density. From the results, it can be assumed that RYT could be reused in the composting process if OFMSW, YT, and RYT are used in the correct quantities to balance the mixture but they cannot totally replace the features of YT. (C) 2009 Elsevier Ltd. All rights reserved.