There's 4 patches per Yew:
A. West Yew (on the other side of the inlet - probably one of the least-visited areas of mainland UO outside of Halloween)
B. The farm south of the sheep farm
C. the 4 square patches along the East edge (near the stable-type NPCs)
D. The vineyards also produce pumpkins
Also, While the Haven and Ocllo patches are roughly in the same area, divergent development of the two cities over the last 10 years has led to the patches being slightly different in shape and size, even though they still correspond 1 for 1 with each other.
Skara:
A. The Big field at top (that someone camps every year on my shard, and wipes it so clean that it seems nothing spawns there)
B. 4 parallel small fields to the south of the house with the brigand.
C. A little farther south, 2 more medium sized plots
D. The three gardens with vine-type plants, usually with someone's castle or keep right up against them on the south edge.
Moonglow:
A. Wheat Fields (east coast)
B. Cotton Field (south coast - most of the time I refer to it as the Bunny field, as that's where my first guild hunted Vorpals).
C. Fenced-in field on SW corner. In Fel, that's right by that faction stone/entrance. In trammel Friday night on LA, some wiseguy filled it up with ki-rin, and getting near it would be lethal for a necro. Heck, I saw a pumpkin in there, prodded it to get it to spawn, and the accumulation of Ki-rin killed it IN LESS THAN 2 SECONDS.