Every time you allow seed to form and mature on your plants, you're taking a chance that those seed will fall, blow, or be dropped by birds some distance
away to sprout and produce new plants. In your gatdengatden, self-sown seeding can be useful for filling new areas or to serve as replacements for perent plants that have died out over the winter. If you don't want them,you can easily pull or dig them out while they're small or else top off your garden with a fresh layer of mulch rach sping to stop many of them from sprouting