Grain was commonly sown by broadcasting seed across a prepared or partially prepared field. Fields were not necessarily divided from paths by fences, so compacted footpaths could cross cultivated land. Limestone close beneath the soil could create shallow patches where plants sprang up quickly but could not develop deep roots. Thorn roots remaining in the ground could compete with a crop even after visible brush had been cleared.
Ancient harvests varied greatly with soil, rainfall, pests, and local conditions. Jesus' references to thirtyfold, sixtyfold, and a hundredfold therefore create an image of striking fruitfulness rather than a technical statement about normal agricultural yields.
Mark and Matthew also place Jesus in a boat while the crowd remains on the shore, a practical arrangement that fits teaching beside the Sea of Galilee.