No there is no way to ensure that the crop takes care of itself until harvest. The only way to achieve this is to create your own world that allows you to control the elements. When you grow anything outdoors you run the risk of your crop potentially being ruined. Think about farmers, they can plant and plow and weed until their hearts content, but the success of their crop depends on the uncontrollable weather. The upside to guerilla gardening is that some of the best marijuana strains are grown outside.