If you are able to unscrew the rods that run horizontally through the radiator from end to end then the radiators may come apart into sections when hit gently with a sledgehammer. Otherwise the radiator is probably brittle enough that vigorous blows from a sledgehammer will shatter it.
Using Craig's List you might get some strong guys to come over and take the radiators away for you (or maybe you may even get some money for them), provided you did not shatter them first.
Do you get coverage you can count on? From the bag of fertilizer? From your lawn sprinklers?