I visited a food pantry garden today where the head gardener said she had done a PDC in Eugene. I saw raised beds with drip irrigation and continuous rows of two or three plant species per bed. Is that polyculture? I'm new to permaculture and have not taken a PDC, but I was expecting to see more of a jumble of species mixed up, no two of the same thing together. Not to mention that I expected to see hugelkultur, keyhole beds, sun catchers & guilds, which were absent from what I could tell. The gardener said it would be impractical to mix it up more in an operation of that size trying to feed the hungry masses. I felt disappointed to hear that. Granted this was much more diverse than the acres and acres of a single plant species in a conventional farm. But how big does a group of one species have to get before it's considered monoculture?
monoculture is cultivation of one crop/plant......a good example is a lawn where people strive to grow only 1 species of grass in a given space.......there are many "levels" of permaculture some people at the bottom have only a basic setup (like the garden you visited) and then there are those at the top who go to extreme lengths to control every aspect of the environment so they have maximum output for very little input.
That is a basic polyculture. It means a collection of pests will all have to arrive at the same time to destroy all the crops and allows a certain amount of redundancy. It also probably allows for simpler (albeit more frequent) maintenance of those conditions.
My area is a total hodgepodge of species with a little bit of design and a whole lot of 'let's see what happens.' I like mine better because the area largely takes care of itself and looks a little like a jungle of corn, sunflower, fennel, quinoa and pumpkin. That doesn't mean that it's better than what your gardener is doing, but it's better for me.
Monoculture is the attempt to grow one variety of one species and (more or less) exclude the rest of existence in that quest, including but not limited to soil organisms, various insects, some mammals like mice, rats, and birds, fungi...
Polyculture is the attempt to grow 3 or more species in close proximity. 2 cultures would just be companion planting.
And that's about it. Anything else is pretty much fair game with how one goes about cultivating those species.
The garden you saw probably is in line with synergistic gardening from Emilia Hazlip. The gardens I've seen using that technique do the things you saw: raised beds, no-till from 2nd year on, no fertilizer that comes from outside the garden, drip irrigation, and spaced planting. There are rules for where you put which plants.
We worked with that model until we realized it was totally unworkable on our site, mainly due to the lack of water and the lack of a balanced mineral base. We now grow much much closer and after working with a polyculture strategy that was very random we are now working to develop better arrangements of plants based on our experience of how plants grow.