Mary-Anne, Be sure to "dirt" your potatos. Pull loose dirt, compost, straw, etc. to just under the leaves. Do this weekly or as often as necessary to keep the potato plant nearly buried. All potatos will be made between the seed piece and the top of the ground. "Dirting" makes the area in which the potatos grow considerably larger. It also helps protect against insect pests that bore into the stem and those that suck on the stem and the leaves. Keep your potatos evenly moist. If you have roller coaster dry to wet spells it will cause the potatos to become deformed. Even moisture will help prevent hollow heart and black heart. I fertilize my potatos once, at planting time. I bury the fertilizer 2-4 inches deeper than the seed pieces. I have found it difficult to "side dress" potatos. Allen Bastrop Co., SE Central TX Zone 8