My father sets these big black tubs filled with mineral lick out for his cows. He gets them from the local feed and seed store. When the cows have licked them clean I take them; drill some holes in the bottom and use them as planters. They are way bigger than the 5 gallon buckets a lot of people use. They will hold about 2 of the 50 pound sacks of top soil. The larger size seems to dry out more slowly. During these mild spring days I don't even have to water every day and even in the summer I never have to water more than once a day.