You would also need planning consent for either of them if it involved change of use of the land. This is not an issue with a normal domestic garden but on large properties with grounds, one cannot assume that the whole of the area of the land around the house has residential status - some may have agricultural or be padock. The area of immediate land regarded as part of the garden is referred to as the 'curtiledge'. Planning Authority will advise.
Usual objections, if planning consent is required, are ones of visual impact on the landscape quality.