Patches allow you to save space on your reef by letting you combine four plants on one space. On high levels you will have problems finding free space on your reef and patches definitely help. On Level 47 for example you can combine four Red Christmas Tree Corals in one patch delivering 1000 Algae each 5h! The number of available patches increases with each level, as well as the vitality.
The following table illustrates the various decorative items available from the Specials tab of Nursery items. It should be noted that some items were limited-time offers, and are no longer available. Also, some previously limited items have recently become regularly available on most platforms (Windows being the exception.)