2-Benzoylcyclohexane-1,3-diones of formula I : where: R1 and R2 are each hydrogen, mercapto, nitro, halogen, cyano, thiocyanato, alkyl, haloalkyl, alkoxy, alkenyl, alkynyl, —OR3, —OCOR3, —OSO2R3, —S(O)nR3 (n=0, 1, 2), —SO2OR3, —SO2N(R3)2, —NR3SO2R3 or —NR3COR3; R3 is hydrogen or optionally substituted alkyl, haloalkyl, alkenyl, alkynyl, phenyl or phenylalkyl; Q is optionally substituted cyclohexane-2-yl-1,3-dione; X1 is optionally substituted alkylene, propenylene, alkenylene or alkynylene; R4 is hydrogen or optionally substituted alkyl, alkenyl, alkynyl, phenyl, phenylalkyl; Het is a three- to six-membered, optionally substituted heterocyclic or heteroaromatic group; and agriculturally useful salts thereof, processes and intermediates for preparing compounds of formula I, compositions comprising them, and the use of the compounds of formula I and the compositions comprising them for controlling harmful plants are described.