Grow them close together so that the pollen from the top can pollinate it's neighbour. Don't plant them too far apart or you will have no corns. You could try different varieties. I direct sowed mine and nothing came up, so I bought another packet and we were enjoying ours last night. Most rewarding. Also might be a good idea to sow them indoors to give them a good head start. For me, I don't like the idea as transplanting them out means I have to use slug pellets. Good luck.