Abstract: A method of supplying plants with iron which comprises applying to the plants, or to the substrate in which they grow, at least one ferrocene derivative of the formula ##STR1## wherein R represents alkyl with 3 to 20 carbon atoms, preferably 7 to 20 carbon atoms, alone or in admixture with a diluent or carrier.

Abstract: A fertilizer composition for supplying plants with nutrient iron containing as an active ingredient at least prussiate of the formula ##STR1## in which M represents an alkali metal ion, alkaline earth metal ion, heavy metal ion or ammonium ion or a proton,R.sup.1, r.sup.2, r.sup.3 and R.sup.4, independently of one another, each represent hydrogen, alkyl, hydroxyalkyl, cycloalkyl, optionally substituted aryl or aralkyl orR.sup.1, together with R.sup.2, and/or R.sup.3, together with R.sup.4, represent an alkylene group, a bis-alkylene ether group or a bis-alkylene thioether group or, together with the adjacent nitrogen atom, form an unsaturated heterocyclic ring, orR.sup.2 and R.sup.4 each represent hydrogen, alkyl or hydroxyalkyl and at the same timeR.sup.1 and R.sup.

Abstract: Ferrocene derivatives of the formula ##STR1## IN WHICH R represents the group COOR.sup.1,in whichR.sup.1 represents hydrogen, alkyl, one equivalent of an alkali metal, alkaline earth metal or heavy metal cation, or an ammonium cation in which one or moreHydrogen atoms can be replaced by alkyl,Or R represents the group COR.sup.2in whichR.sup.2 represents optionally substituted alkyl, optionally substituted alkenyl, optionally substituted cycloalkyl, optionally substituted cycloalkenyl or optionally substituted phenyl,OrR represents the group ##STR2## in which R.sup.3 represents hydrogen or alkyl andR.sup.4 represents a ureido or thioureido radical, a radical of the formula --CH.sub.2 --CH.sub.2 --N.dbd.CH--ferrocene, a 5-membered or 6-membered heterocyclic radical or a group of the formula --OR.sup.5 or --NH-R.sup.6,in whichR.sup.

Abstract: Plants suffering from micro-nutrient deficiences are treated with prussiates of the formulaM.sub.a [Fe(CN).sub.5 X].sub.bIn whichM is an alkali metal ion, alkaline earth metal ion, heavy metal ion, ammonium ion or hydrogen,X is a group which can occupy the sixth coordination position on the iron, or a suitable organic radical,A is 2, 3, 4 or 5, andB is 1, 2 or 3.The prussiate may be present as a hydrate and/or may be in admixture with a carrier.