Wiktionary
a. not deliberately planted but just growing, often in a garden from wild seed - usually refers to domestic plants and to plants that have escaped and become naturalised.
WordNet
adj. growing from seed dispersed by natural agency such as wind or birds [syn: self-seeded, self-sowed]
Usage examples of "self-sown".
Here there are extensive heaths, with a few clumps of old Scotch firs on the distant hill-tops: within the last ten years large spaces have been enclosed, and self-sown firs are now springing up in multitudes, so close together that all cannot live.
And the second day they were deep in open fields where patches of self-sown grain rippled ripely under the sun.
He ate as he went, berries and handfuls of ripe grain pulled from the ragged self-sown patches in the old fields.
To the north and east, and to the west beyond the valley, it was sheltered by the great forest of Andredeswald, stretching forty miles northward towards the town of London and over a hundred miles from east to west, a natural self-sown forest untouched by man, of native oak, beech, chestnut, ash, birch and holly, and conifers where they were favoured by the soil.