Euphorbia can suffer from mildew. It can also expand with underground root shoots. Spurge can cause an allergic reaction on the skin. To be safe, always wear gardening gloves while gardening. After flowering, cut away only the spent flower stems down to the ground. Be careful, the white milky sap that is released is poisonous. Euphorbia likes a sunny spot in the border.
General care tips can be found here