An easy way to add definition between your lawn and landscape beds is to plant border grasses like mondo grass.
Border grasses are perennial, and can range in size from 2 inches to 2 feet tall.
Mondo grass (Ophiopogon japonicus) is one of the most popular border grasses. It has deep green, variegated, or black foliage, and ranges from 2 to 24 inches in height. It's sometimes planted as a groundcover, creating a shade-tolerant lawn alternative.
Mondo grass is quite often confused with liriope, which is now listed as a high invasion risk by the UF/IFAS Assessment of Non-native Plants in Florida's Natural Areas and no longer recommended. Common names such as Aztec grass and monkey grass are used for both. However, the leaves of mondo grass are more narrow than those of liriope and have smaller fruit.
Border grasses are relatively low maintenance once established, though they'll look better if you mow or cut them back in late winter or early spring.