More information about, how to feed and look after laying hens in your garden here; How to keep garden hens
Mixed Poultry Grit is a combination of soluble and non-soluble grits to help maintain a healthy hen, ensuring your poultry has essential minerals.
Yes you can feed hens garden produce and leftover cooked fruit and vegetables.
Hens housed in a coop and chicken run that don't have access to green stuff will benefit from and enjoy being fed cabbage and other fruit and vegetable kitchen leftovers.
Hens kept in the garden for eggs, actually enjoy vegetable peels, bananas, apple cores, carrots, broccoli even spaghetti and porridge. In fact, laying hens can be fed almost any wholesome food, vegetable or fruit you eat yourself. If you can eat it so can your hens and you can feed them this daily as part of a balanced diet. That should include the mixed corn, layers pellets and grit I have listed above.
I have found over the many years I have kept layers. That. one of the many benefits of keeping chickens is most of my kitchen waste and stuff I grow in my garden. Can be fed to them ensuring they get a varied and balanced diet, saving me some money too.
Avoid feeding your chickens any raw green peels (such as green potato peel) and citric fruits such as oranges and lemons. All fatty foods or foods with a lot of salt in it, also sweets (to much sugar) and processed food (to much of everything that is bad) and poisonous garden plants and weeds like foxgloves and bindweed. If it is bad for you it is bad for your hens.
Chickens are fairly good at knowing what not to eat and will avoid anything really nasty.
One of the most important things to provide for chickens in freezing weather is fresh water, remember to break up any ice that forms on top. Check the water two or three times a day and change it if it gets muddy.
My article about feeding laying hens looking after chickens in your garden