grow them in the summer. I grow out fish in a pond here (oklahoma) and they grow real nice real fast. and they can fight eachother in a large volume to increase head and colour of the dominant fish. However, my rule is that I do not let them get below 60 degrees, I have read that most tropical cichlids start to undergo hypothermia at 40 degrees (f).
Also, once when a few of my heaters went out last winter, the water went down to the 50s approaching 40s and I watched a medium size (5 inch) red devil (labiatus) in one of my tanks loose conciousness.. of course i moved him right away to a heated tank and he was fine within an hour or so. It is notable though that at these same temperatures I did not see as great an effect on jack dempsies or convict cichlids, as i had too many juvies at the time to have all of them get heaters. They just hid all the time which isnt a good sign, but they were fine for a week or so until I was able to get everything going again.
So in short, I would not do what you proposed from my own experience. however growing out cichlids in ponds is great for them... Ive pulled out 1 inch convict cichlids from my pond that already had little koks.
As for my experience growing them out in ponds...
Growing out FH in pond you will most likley have to deal with them adjusting to a large environment. whenever i pull dominant cichlids out of ponds (unless theyre real sociable like cons) they have adjusted to having a larger territory than the average size tank (think 4 inch red devils wanting a 75 to themselves). so if you were growing out FH in ponds over the summer you should be prepared to give them all their own tank when you pull them, unless two have paired off. Ponds are also great for letting groups select pairs. However, you can potentially curb this problem by overstocking the pond if given proper filtration. I have not tried this however as the pond i use is relativeley natural, relying only on moderate bio filtration.
Another potential problem is birds, though putting a bunch of rocks and pottery in there means i have had no problems with herons and the like, which we do have here. Snapping turtles also pose a threat, though they prefer large bodies of water so you're safe from that if your pond is small. Overall though I would suggest covering the top of the pond with something like chicken wire if you can. Racoons are also excellent fisherman.
Because you're in california I can also include that I have been researching the climate there, as I am hoping to move there in a few years so I can farm cichlids outside. Southern california seems to be the only other place in the continental us besides florida where tropical fish can be grown outside without much cold danger. However, from my research I have concluded that this could only be potentially done south of san diego, very close to the mexican border. It is the tropical terrestrial air mass colliding with the tropical maritime air mass that makes this possible, rather than equatorial adjacentness... so you get the most information based on weather. the intersection of two similar air masses makes the weather more constant, which is what most fish from equatorial regions are adapted to. An added plus is that this means it is possible to calculate the exact location that is best to keep cichlids in california. However I have not done the appropriate research, as my move is still a couple years away : )
Best of luck buddy. If you're planning to grow out fh for sale then keeping them in a pond is by far the best option imo. you can grow out a batch and select the MP's to keep or get yourself a solid breeding pair. However, if you are just looking to keep them, aquariums will be your best bet. In a pond you cannot have the relationship with a fish you do in an aquarium.
