Thank you for sending the photo - it looks like your hedge is made from boxwood (Buxus sempervirens) and there are more than 70 varieties of boxwood but all will take frequent pruning making them great hedge and topiary plants. The yellow leaves could be due to winter injury if cold winds hit the plants, or poor drainage if heavy rains cause water to settle near the roots and your soil has lots of clay. (Poke holes down deep with a large screwdriver). But the yellow patches could also be due to Boxwood Decline disease and there is no cure. Your plants can outgrow the problem with good drainage, proper watering (one inch of water a week in summer) and by collecting all the pruning crumbs or cut leaves when you trim. Try not pruning on a wet and warm day as this is when disease spreads most easily. Keeping the plants healthy also means not over feeding. One application of slow release plant food like Osmocote in the spring is enough fertilizer for any shrub and if your soil is good and your shrubs healthy they don't need any fertilizer. I would cut out the yellow patches and see if no spring growth appears to cover the bare spots. Good luck and Keep growing, Marianne Binetti