Basic Troughs. Troughs should be no less than 6 inches deep inside. Ensure you have at least 2 holes for drainage. Soil mixture should be gritty-typical mix: 50% loamy soil with equal proportions of sand and peat moss (you may add some small stones or perlite) _____________________________________________________________ Mixtures for Troughs 2 parts Portland Cement 3 parts Horticultural Perlite 3 parts Peat Moss OR 1 parts Portland cement 1 part sand 1 part Peat Moss