But I love that discussion soo much... almost as much as I love pizza!!! 
Sure! 
Pizza is brain food, crucial for all those concentration rolls 
Speaking for my Saga, our covenant has control of three villages, but we receive little excess food from these (still, every little helps). Our covenant also has its own fields that, with the advantage of our enchanted plow means we get good yields from them.
Our covenant also has a large herd of goats and sheep and a decent flock of chickens.
For goods outside this, we trade.
Although much of agriculture was subsisdence farming, the average covenant has magical means to vastly increase crop yields. In our case, the magical plow allows the fields to be plowed in a fraction of the time it would usually take and with far less effort, leaving our farmers free to engage in other farming activities that they usually might not have time to do so well. The plow was easy to make too.
IMS the covenant controls 1 village only, and it is NOT a village dedicated to agriculture. What it is in practical terms is the place where the foresters and woodcutters of the covenant live. We reached an agreement with the local lord to exploit some of the wild forests under his nominal control. We have foresters there, and exploit the wood and pay him a fixed cannon renegotiated every 15 years. It consists of certain ammounts of certain woods, some ammounts of pelts (and foresters in case the nobility want to go hunting in the forest) and some hard silver as well. He gets revenue that he was not geting before, and we get a place to live and resources.
We have increased our business to shipbuilding using that said wood as well, sending the wood to a city with a dock on the coast floating in the river.
We get our food from the forest and buying it from other sources. Since we do not produce our food, we might have problems feeding us in the future (potential story hook) if there is a famine in the arwea or something, but it is not a biggie for us. We pay it at quite a high price, since we tend to buy it a little far away from home, but no biggie since our buisiness is doing pretty OK right now.
Cheers,
Xavi
Our covenant started out as poor, we only had a village of fishermen. (minor source of income)
We have negotiated forresting rights from the local lord as well now. And sometimes we cast a nice agricultural boosting ritual to have some serious plants growth.
I think every covenant needs to come up with its own answer to this question. A lot of groups make securing and maintaining the covenant's income sources into a major element of their stories. Others prefer to dwell on magical matters and leave the details of finance and logistics vague.
Edit: The reason I speak of income instead of food is that I see the medieval economy as commodity based. That is, food and money are equivalent at some level.
So my first piece of advice is to talk this over with your players and decide whether you want income to be in the foreground or the background of your stories. In my Saga, it is in the background.
The second thing I would like to say is that a Spring covenant might have trouble supporting 50 people. But does it need 50 people? In Chapter 6 of the rule book, a baseline covenant has one warrior and two servants per magus. So a covenant of 4 wizards would have only 16 people, counting the wizards.
Actually, food "is" the currency, quite often, as at this time Europe was only just shifting away from a barter economy at the peasant level, and would not universally be accepting a "coin of the realm" for quite a while.
It's far too easy for a StoryGuide to fall back on fantasy RPG practices, and have the travelling magi throw silver pennies around as they go, when in fact many villages, especially ones not on major roads, would have nowhere to spend "coins", and thus would probably be more than hesitant to accept them as payment.
"Don't care how many o' them silver pennies ya got... but that walkin' stick o' yers is mighty fancy..."
While I can mostly agree with the resume of the topic given here, I have to strongly object on the fact that Option B) if it last long enough to be digested, it's nutritous, would not have any support in the rules. It does, from the fact that that magically-created things can have effects on the mundane world that outlast the spell's duration. A magically conjured horse leaves hoofprints on the ground, a magically created fire can burn down a house.
But anyway, fully acknowledging that the topic was and is way contentious (since the rules are rather contradictory on this point, and differing views hearken to different feelings about what is the "right" amount of Hermetic magi's authonomy from mundane chores and support, different interpretations of the paradigm, and so forth) I do proceed to post the links to IMO the most comprehensive discussions of the topic
As well as the FAQ entry on this very topic:
(ignore)
Thank you for the thoughtful responses.
The debate about magically created food is very interesting but, after talking about it, in our saga we prefer not to be able to solve this problem as easily as that. Therefore, we won't be able to create nourishing food without vis. We don't want getting food to be one of the main foci of our saga, but it seems a good way to force the covenant to have relationships with neighbouring mundanes and the need of getting external supplies is a vulnerability that can be exploited in some stories (vulnerabilities are always interesting). Of course, that's good for a spring covenant; as the covenant grows more powerful it will likely have less mundane supplies-related problems.
Thanks also for the suggestions and examples about how food supply can be arranged.
Gribble, what's your covenant's relationship with surrounding nobility like? Why do they accept that bunch of "weird" people's holding land?
The covenant of Dua Fluminus in the Rhine Tribunal has for a long time been living supported by import from the neighboring towns. (Funds being provided by wealthy sponsors). Due to local warfare this is becoming less reliable, so in the year of our Lord 1235, the Magus Draco of house Bonisagus presented his solution: Conjuration of the Baker's gold. This is a 5th magnitude CrHe spell that produces about 1 million loaves of bread. This has the advantage of using Herbam vis (which is the only sort the covenant has a considerable surplus of). The versjon now held in Duenmar was a side-effect (major), causing a field of grain (same sort as used in the bread) to spout whereever it is cast. It is strongly advised that you have some storage in mind when the spell is cast - preferably a magical storage, as the loaves may not keep overly long othervise...
Our covenant (not Gribble's) has good ties with the local nobility, now that we helped them to power. They still don't really like all those 'funny people' though.
We've held big crop ceremonies a couple of times, which most villagers did like. (especially when they saw the increased yield the next year)
Then again, the locals are used to the nearby fairies. The earth fairies are very friendly and helpfull most of the time and our villagers often lend them their tools (which they always get back nicely cleaned).
Older covenants, or those founded by more powerful magi striking out on their own, tend to be either in isolated places or to claim a small ammount of nominally out of the way space in defiance of the local mundanes.
And I tend to favor the later. Bear in mind how unbelievably powerful magi can be in regards to conflict with mundanes. Given, they don't usually seek said conflict, yet they also have a sizable contempt for mundanes.
Arrangements/Deals with mundane lords can be bones of contention with older/prideful magi. Some of the oldest covenants are actually fortresses that dominate the local landscape are simply known to be left alone by mundane authorities... because they know better. And that really is the 'ideal' that Magi are looking for. Not all can achieve it by any means, but most wish they could.
For a factual basis I would suggest the book "The Medieval Village", likely in the covenent book list of references. By 1200 the agricultural technology was fairly well advanced and certainly surpluses existed but the transport technology was lacking. Moving food long distances by road for example would be very difficult, something which plagued armies of the day, infact something which plagued armies until around the time of Napolean.
Additionally, and most critically there were no "free" villages. So the village belongs to someones Fief, and in this case there is feudal ties required to tax the village. So if the covenent is drawing resources from the village then it owes something to the local nobility...and there is that clause in the Order of Hermes rules and regulations.
The simplist solution is that there are farmers in the grogs. With a bit of CrHe (possibly this is more MuHe) or ReHe and ReAu you can ensure bumper crops I would imagine. Now an easy way to deal with this is to get a copy of "Harn Manor 2nd Edition." This gives you rules for making up a manor and calculating surpluses and such (you don't need the Harn rules to use the Manor suplement). It also gives you some very good rules for weather effect, random events, fief development etc. This is probably more detailed then most people would like though.
However, a covenent needs several acres of crops to feed a family of 4-5 for a year. Plus you need a variety of crops for health reasons, and even the poorest person would have about an acre of land planted in a garden and for their hovel, but they would be dependant on laboring for others. A rich serf might have 10-20 acres plus additional acres under cultivation. This at the least gives you some idea what scale of agriculure you need.
No matter where you are, no matter what else you have each household has a garden, and there is likely several tens to hundreds of acres under cultivation plus forestry (and pig herding, charcoal burning, forestry), and animal pasturage (cows and sheep). The ratio of the three or four, if you include fishing, is determined by the nature of the land. However, there will be always some cleared land used for crops, some pasturage and some forests (assuming you are rural based covenent).
Also forget the 1800's north america where farm houses are spread out on huge plots of land Midieval villages are clusters of houses surrounded by the fields and pasturages.
There is no particular reason why a covenent would not have a fairly goodly number of grogs engaged in agricultural pursuits. Not doing this would actualy make the covenent stand out like a sore thumb to any mundane who saw it.
But this all depends on how realistic your setting is, also where your covenent is located plays a major role.
There is a ReHe spell that makes a tree blossom and give fruit in about a day.
Could a version of that be used to make a group of plants do the same?
That would make the "how to feed a covenant" problem no problem at all.
Do that with 2-3 kinds of cereal during a month in a Room (or structure) sized space. Thetre you go: mass production of rye, wheat, corn and whatever you are planting there. You kill trhe plant after its flowering / fruit, so no biggie in it not providing food in the future.
NOw,l that can break the economy of a region easily, if abused, but it seems a good wayu of passing over the land restrictions for me. A peripheral code on food production is likely to exist as there are provisions on silver generation in some peripheral codes. Easy
Now, warping of the people being fed on this production might become problematic if the SG so desires....
Xavi
Also, a big part of agriculture is sustainability. Iirc, a ReHe spell like that produces seedless fruit, so no seeds for the next planting. Awkward.
Is it seedless? Damn. 
Problems for not having the books with me 
Still, a 2 room system can work:
- one room with a controlled environment to make the food grow as normal, but extra-healthy. This seeds would then all be yused in the next plantation
- A second room with the fast growing cereals using 8/10 or 9/10 of the total seeds that you grew in the first room. No need for seeds if tyou are going to eat it. It is still nutritious.
Requires WAAAAY less space than the usual extensive farming. Kind of a greenhouse approach to farming.
Cheers,
Xavi
If this is Geis and Geis, it was used, but it is credited as "Life in Medieval Times". Bascially this is three Geis and Geis books published in a single volume. Yes, for medieval entry level history, it's excellent.
As the book is on the other side of the Atlantic I can't be 100% certain but Geis and Geis sounds right. It was a husband and wife team, I have two of the apparently 3 books.
I don't know what level the books are, as History isn't my field but I found them very well written and they go a long way towards "enlightening" people on the way life was. Entry level sounds right thinking on it. My interest lies more in Military History. I read them for background to help my gamemastering. I even took a course in university on Human Geography to help me design my worlds better.
I can only add my recomendation to read them (or this compilation book Timothy Ferguson mentioned), along with: "A World Lit Only By Fire" and "A Distant Mirror." Both of which are more general introduction to things Midieval.
Anyway back to feeding covenents.
My character's opinion would be to use magik in a subtle way rather than an overt way. There are a lot of things you can do with magik to: make food spoil less, make yields higher, make harvesting efficient, and even to transport food. But this is a matter of taste.
Speaking as a gamemaster I would say that you loose story opportunities if the food is from the local Mage-O-Mart. But again this is a matter of taste. Hmm...pardon the unintended pun.