Conventional horticultural systems grow one vegetable in each field or bed. Polyveg systems grow several different vegetables in the same field or bed.

The different crops complement each other through different growing heights, different root depths, different nutrient needs and symbiotic relationships. The best known example is the Native American system 'three sisters' where sweetcorn, climbing beans and pumpkins are grown together, but many other combinations are possible, including mixtures of annual and perennial crops. The yield from each crop is lower than in a conventional system, but the overall yield from all three crops is greater.