The best plants to grow between patio pavers are hardy perennials or self-seeding annuals that are shallow-rooted, friendly to bare feet and easily maintained. Choose plants that are fast-spreading and---most importantly---won't establish giant root systems that heave the pavers out of place. In addition, these patio plants should visually soften the hard edges of the patio's stone work and look natural yet deliberate, rather than weedy and unkempt.
Shaded patios look ancient and mysterious when moss creeps between slabs or bricks. Mail order companies now offer a staggering collection for those interested in growing more than one kind of moss throughout the patio. Even easier, however, is to simply transplant the moss growing in moist spots on your property and by pressing it gently between patio slabs. Cut strips or irregular pieces to fit the bare spaces between pavers, add soil and gently press the moss where you'd like it to grow. Moss grows by rhizoids rather than roots, making it remarkably tolerant of this rough treatment. Water the moss thoroughly every day until it is established---about three weeks. Many gardeners cover the moss with boards during this phase.
Renowned for the velvety softness of its tiny leaves and for its heavenly smell when trod upon, thyme adds the advantage of being a culinary, as well as ornamental, herb. Choose creeping varieties rather than upright ones to give a lush, spilling effect between pavers. Transplant seedlings in late spring, adding a bit of sand to the soil. Thyme does best in sunny, dry locations. In late summer most thyme plants erupt into a carpet of white, pink or lavender flowers.
"Like a chamomile bed---the more it is trodden the more it will spread." As the ancient proverb proclaims, this apple-scented herb is one tough little plant, despite its feathery-looking foliage. Chamomile brings many of the same qualities to a patio that thyme does. Both herbs crave sunny conditions, both thrive in cramped quarters and both provide a soft, fragrant cushion for bare feet. Harvest the cheerful yellow flowers to make calming teas or herbal hair rinses that brighten blond hair. As with thyme, chamomile appreciates a bit of sand when planted to help it get established, and dislikes over-watering.
The fragrant, tiny flowers of alyssum lend a lacy quality to hard-edged patio pavers. "[T]he best thing about it is that you can easily grab little clumps of the flowers whenever you need them and stick them into whatever corner needs a carpetlike path---even the soil between flagstones," writes garden author Barabara Damrosh. Alyssum blossoms are usually white, but some nurseries also offer pink and lavender varieties. Either sow seeds between pavers in the spring, or transplant seedlings. The plant self-seeds freely, so it rarely needs replacing.
Mazus reptan, or cupflower, looks lovely in irregular-shaped paving situations where the small, tubular purple flowers show through the stones' cracks. Hardy to zone 5, cupflower tolerates either full sun or part shade. Gardeners growing north of zone 5 may still have good luck with cupflower on a sunny patio, because the stones retain heat even during winter months.
A densely matting plant, Herniaria, or Green Carpet, adds feathery bright green or golden color to a patio, a valuable feature for twilight gatherings. Its arching branches tolerate foot traffic, although not as much as thyme or chamomile. This plant prefers full sun or part shade, and likes either regular or sandy soil conditions.