We reuse the cardboard inner tubes of toilet rolls and kitchen towels by filling them with compost and growing carrots, parsnips and leeks in them. Most root vegetables do not like to be disturbed once they begin to grow. If they are knocked and bashed about they tend to die off. (I think this was the problem in out first year). So we plant the seeds in the tubes, and when they have started to grow we plant the whole tube out. As the tube is made of cardboard it degrades in the ground, which has the added benefit of nourishing the soil.