Hi Laureen, but, what do you mean by self-sufficiency of a castle?
I don't think that I could live on a diet of raw pigeon and water.

I'm going to let Laureen answer that one

During the great siege of Rochester castle of 1215 http://myweb.tiscali.co.uk/castles/page34.html the rebels were reduced to eating the flesh of their own horses.
A castle could never be self sufficient and a favourite method of taking a castle
was to cut off its supply lines.
Having said that, Edward the first, in building his Welsh castles on the shore enabled him to re-supply his castles by sea.
However, a castle could never be self sufficient.

Maybe you could offer up some incite to the bases of why you have the opinion that a castle couldn't be self sufficient?
Listing some old texts, books, journals or papers on trade might also be useful to our members.

A castle had to be supplied from the outside.
Nothing was grown or produced in the form of food or fuel.
Castles were not occupied by the lord or king all year round,
in order to feed his staff he would have to move from place to place.
A good read on the subject of medieval life is: 1215 The year of magna carta by Danny Danziger and John Gillingham.

Thanks for the info Paul. Maybe a better a better word choice is "workings". I'm interested in learning about the daily "goings on" of castles as well as their construction.

Maybe an depth look into smaller castles would also provide a better understanding of what was actually done.

True in terms of the castle building, but in terms of the estate it administered and accepted rentals on it probably could be self sufficient since more often than not rents were paid in goods rather than money.
The function of the estate and the castle were integral, each providing essential service to the other. Isolate the castle from it's estate by siege and yes Paul is entirely correct, but as an integral part of the whole under normal operating conditions then yes it could be self sufficient, since if the estate could not break even or operate at a profit by selling on excess goods taken as rental, then like any modern business, it would go under. The key question is whether a castle produced a wide enough range of goods from it's estate to avoid dependancy on basic necessities being imported from a market outwith the estate,
and I'm sure there must have been plenty that were, since most had their castletowns which served their need for 'service' industries.
The key to making a castle impregnable lay not only in architecture, but it's ability to hold enough stores to survive a siege, where the supplies to the beseiger dried up before the stores of the castle.

and a small castle with its live stock and stores in side the Barmkin wall could be more self reliant if it had a garden as well and many did.
The hardest part is keeping the animals with out and the livestock out of the garden in such a case!

A fair point, since many of the smaller castles , bastles and towers were in normal function laird's houses, later suceeded by farm houses, and were unlikely to be beseiged.
A serious attack by say an invading army would destroy it, but for the most part these smaller places were built to defend against small raiding parties, and in such a function of everyday life many were self sufficient as farms.