Each donkey requires an absolute minimum of ½ acre, however modern thinking on managing grassland in a more environmentally friendly way, allowing wild flowers to grow etc, recommends about 5 times as much. Assuming you have two donkeys, you will need at least one acre. This area should be safely fenced - safe so they are kept in, and safe so it cannot harm them (no loose barbed wire!). Donkeys usually respect electric fencing, but the very hairy ones can walk through it with no effect, and I personally would never use it as my sole barrier to anywhere dangerous. You will almost certainly need to sub-divide your land into smaller areas, to restrict grazing in the spring and summer months, for weed-killing and fertilsing and to minimise poaching of the soil in wet winters – this is where I would use electric fencing for internal divisions.
You must make sure that the field does not have any poisonous plans or tress growing in it – as well as ensuring the obvious dangers like deep holes, bits of old wire etc, are not there to cause an accident. Yew is a killer, so make sure non-overhangs the field. Ragwort is also a killer, they probably won’t eat it when it is actively growing, but it loses its bitter taste when dead so will be lethal in hay or as ‘dead stalks’ in your field. Please use the buttons on the left to find out more about poisonous plants. Grass cutitngs are also lethal as they ferment in the stomach almost always causing severe colic and death. Make sure that no 'helpful neighbours' tip theirs over in a mistaken belief that the donkeys will enjoy them.
Gates must be secure – donkeys are very clever at working things out and can learn how to open an ‘easy one’ if there is something more interesting the other side – and remember what I said about wood!
An ample supply of fresh water is also obviously essential.
Donkeys do not need, and should not have, lush grass. Do not think of rich meadows, instead remember where nature designed them to live – rough bush and scrub land - and recognise that keeping them on rich grazing is likely to give you management or donkey-health issues. Donkeys will eat all that grass, but would actually prefer an area with brambles, bits of hedge etc as they are natures browsers more than they are actual grazers. A 'scruffy bit of scrubland' (free of poisonous plants) is far better for them than a rich green cattle pasture.