f you plant them in compost, there will be enough nutrients in that feed for them to survive for a whole year. Remember that growth is slower in the first year than in any others. This is due to the roots becoming established and setting up their base. Once this has been accomplished, the leylandlii will grow without any help from you.
Although we'd love to sell you plant feed by the gallon for your Leylandii, it really isn't needed, keep your money in your pocket.