The present invention relates to methods for preventing or inhibiting damages to plants during cultivation or for preventing growth retardation and to method for pest control in plants, especially methods for preventing, or inhibiting, damages caused by insects to plants. The method comprises the step of contacting said plants and/or a growth substrate for said plants with an aqueous suspension, or mixture, comprising amorphous silica or organic siliceous sedimentary rock wherein said contacting is performed one or more times during the first 50% of the life cycle of said plants and said contacting is not performed during the second 50% of the life cycle of said plants. The present invention relates especially to the application of said methods on chrysanthemum, gerbera, strawberry, peony, lisianthus, orchid, phalenopsis, rose, carnation, lily, iris, freesia, impatiens, spathiphyllum, ranunculus and geranium.
