The array of fruits and vegetables available is quite phenomenal. As a general rule, the rich-colored ones that are low in water content tend to be more nutritious. The dark green and orange plants tend to have more vitamin A, which appears to be important for our feathered friends for a variety of reasons.
Spinach has gained bad press: It is believed to prevent the absorption of calcium. This vegetable is an excellent source of iron and calcium, as well as other nutrients. Again, moderation is the key. Over the years, there have been many lists made as to the warnings of certain plants in this category, but space does not permit me to go into them here. With many plants, you can feed the whole plant to your bird, the green leafy parts, too. If the bird is not eating it, at least it has another toy to play with!
When faced with high produce bills, the owner of a large collection is invariably confronted with the special "vegetable/fruit of the week." The supplier has excess, and he needs to move it fast! Always check these products carefully; some products store well, while others are literally rotting! The nutritional content in the latter rapidly deteriorates, making it pointless to give it to your bird. The possible bacterial and fungal contaminants that are part of the breakdown process can be potential problems for the birds.