Killing weeds is quite easy. All that is required is a systemic weedkiller such as Weedol which is available from garden centres. All professional weedkillers require Pesticide Certification but are cheaper. Systemic weedkillers enter the leaf and then reach the rest of the plant through its vascular system. However it works best when sugars are moving through the plant and that is when it is growing. So the best time to treat weeds is in the growing season.