Rain or watering after you fertilize is a good thing. Osmocote is a slow release plant food that releases nutrients as the soil warms and the soil must also be moist. If your soil is still cool from winter the plant food will not be released as the plants will not yet be actively growing. A heavy rain will not wash away Osmocote so don't worry and expect to enjoy lots of flowers this summer. Keep growing, Marianne Binetti