Substituted 2-benzoylcyclohexane-1,3-diones of the formula I where: R1 and R2 are each hydrogen, mercapto, nitro, halogen, cyano, thiocyanato, C1-C6-alkyl, C1-C6-haloalkyl, C1-C6-alkoxy, C2-C6-alkenyl, C2-C6-alkynyl, —OR3, —OCOR3, —OSO2R3, —S(O)nR3, —SO2OR3, —SO2N(R3)2, —NR3SO2R3 or —NR3COR3; R3 is hydrogen, C1-C6-alkyl, C1-C6-haloalkyl, C2-C6-alkenyl, C2-C6-alkynyl, phenyl or phenyl-C1-C6-alkyl; where the abovementioned alkyl radicals may be partially or fully halogenated and/or may carry one to three of the following groups: hydroxyl, mercapto, amino, cyano, R3, —OR3, —SR3, —N(R3)2, ═NOR3, —OCOR3, —SCOR3, —NR3COR3, —CO2R3, —COSR3, —CON(R3)2, C1-C4-alkyliminooxy, C1-C4-alkoxyamino, C1-C4-alkylcarbonyl, C1-C4-alkoxy-C2-C6-alkoxycarbonyl, C1-C4-alkylsulfonyl, heterocyclyl, heterocyclyloxy, phenyl, benzyl, hetaryl, phenoxy, benzyloxy and hetaryloxy, where the eight last mentioned radicals may in turn be substituted; n is 0, 1 or 2; Q is a cyclohexane-1,3-dione ring with or without substitution which is attached in position 2; X1 is a straight-chain or branched C1-C6-alkylene, a C2-C6-alkenylene or a C2-C6-alkynylene chain, where the abovementioned alkylene, alkenylene or alkynylene radicals may be partially halogenated and/or may carry one to three of the following groups: —OR4, —OCOR4, —OCONHR4 or —OSO2R4; except for those of the abovementioned alkenylene radicals where the double bond is &agr;,&bgr; to the phenyl ring and where Het is linked to the double bond via the &bgr; position; R4 is hydrogen, C1-C6-alkyl, C2-C6-alkenyl, C2-C6-alkynyl, phenyl, phenyl-C1-C6-alkyl, where the abovementioned alkyl, alkenyl or alkynyl radicals may be partially or fully halogenated and/or may be substituted by one or more of the following radicals: hydroxyl, mercapto, amino, cyano, nitro, formyl, C1-C4-alkylamino, C1-C4-dialkylamino, C1-C4-alkoxycarbonyl, C1-C4-alkylcarbonyl, C1-C4-alkylcarbonyloxy, C1-C4-alkyl, C1-C4-haloalkyl, C1-C4-alkylthio, C1-C4-haloalkylthio, C1-C4-alkoxy, C1-C4-haloalkoxy; Het is a three- to six-membered partially or fully saturated heterocyclic group or a three- to six-membered heteroaromatic group having up to three hetero atoms selected from the group consisting of: nitrogen, oxygen or sulfur, where the abovementioned heterocyclic or heteroaromatic group may be partially or fully halogenated and/or may be substituted by R5; R5 is hydrogen, hydroxyl, mercapto, amino, cyano, nitro, formyl, C1-C4-alkylamino, C1-C4-dialkylamino, C1-C4-alkoxycarbonyl, C1-C4-alkylcarbonyl, C1-C4-alkylcarbonyloxy, C1-C4-alkyl, C1-C4-haloalkyl, C1-C4-alkylthio, C1-C4-haloalkylthio, C1-C4-alkoxy, C1-C4-haloalkoxy, where the alkyl radicals may in each case be substituted by in each case one or more of the following radicals: cyano, formyl, C1-C4-alkylamino, C1-C4-dialkylamino, C1-C4-alkoxycarbonyl, C1-C4-alkylcarbonyl, C1-C4-alkylcarbonyloxy, C1-C4-alkyl, C1-C4-haloalkyl, C1-C4-alkylthio, C1-C4-haloalkylthio, C1-C4-alkoxy, C1-C4-haloalkoxy; and agriculturally useful salts thereof, processes and intermediates for preparing compounds of the formula I, compositions comprising them, and the use of the compounds of the formula I and compositions comprising them for controlling harmful plants are described.