Select plants that can be neglected, such as hardy annuals. Biennials are plants that live for two years. The first year they only put up leaves, the second, they bloom, set seed, and die. Much like canons or a round in a song, the trick to these plants is to start them in succession. Once they are established they will reseed and continue for years.
Biennial seeds are best sown in autumn.
Perennials are plants that can live for several years or more. Some easy perennials to grow from seed are evening primrose, lupines and oriental poppies. . Trees, bushes , get them from development sites, or find a decent nursery. Don't be tempted by big specimens, younger plants will adapt and grow faster. Then mulch with carpet or sawdust.