Geese can be fed exclusively on grass if you have enough of it and it is of sufficient quality. Grass contains all of the vitamins and minerals geese need when it is fresh in the Spring.
Grass should be kept short (about 8cm or 3 inches) which can mean frequent mowing or keeping them within a mixed farm system with larger animals that will graze the longer grass first.
If you run out of good clean grass, wheat can be fed in the bottom of a bucket of water. The wheat will sink to the bottom of the bucket and keep rats and mice from eating or contaminating the food. Without grass, a medium size goose will eat around 200g of food per day.
Geese love greens such as cabbage, cauliflower leaves and lettuce. They will also eat leftover vegetables like cooked potatoes, carrots, parsnips etc although not all geese like the same things and usually have to get a taste for things. Generally, it is best to provide a little food for geese to take should they want it for breakfast or before bed.
When the grass is growing well during the spring and summer months, this is rarely needed. Geese should be given wheat and dried poultry layers pellets mixed in equal quantities but not layers mash (as this can get stuck in their mouths). Remember always provide clean fresh drinking water as with other waterfowl.
I provide my geese with ad-lib wheat in a half sized bucket of water and their layers pellets are available ad-lib in a hopper so that they can take what they want of both. Providing wheat in water has the advantage of keeping it away from crows, rats and mice although remember rats need to be near a source of water as well as food so if you see evidence of rats, always remove both food and water overnight.
Geese will normally lay a few more eggs when fed on wheat and pellets however they must not be allowed to get too fat. Scraps such as bread should be regarded as treats and fed only in small quantities.
Geese should always be offered layers pellets during the breeding season to provide calcium but remember layers pellets will soon go bad if they get wet so only feed what they will eat in a breakfast or bedtime meal if you don’t use a waterproof hopper. Mixed poultry grit containing oyster shell should also be provided ad-lib. An easy way to do this is to bury a flowerpot in the ground and peg it down through the holes at the bottom. It can then be filled up with grit and should be free to drain during wet weather.