Along with true grasses (family Poaceae), the genus Carex (sedges) are often included in this classification. Their popularity relates both to their variety and to their three season contribution to the garden. Their long season is related to the lush new leaf growth in spring, and that the summer inflorescences (grass flowers and seed heads) are often dramatic and long lasting. Ornamental grasses can be brown, bluish, red, green, cream, and variegated.

Almost all ornamental grasses are perennials, coming up in spring, from their roots, which have stored large quantities of energy, and in fall or winter go dormant. Some, notably bamboos, are evergreen, and a few are annuals. Sizes vary from a few centimetres up to several metres; the larger bamboos may reach 20 m or more tall. Some ornamental grasses are species that can be grown from seed. Many others are cultivars, and must be propagated by vegetative propagation of an existing plant.

Pampas Grass is easily recognizable and many people have seen small quite blue grasses in commercial landscapes. There are Miscanthus grasses whose variegations are horizontal, and appear even on a cloudy day to be stippled with sunshine. Many Miscanthus and Pennisetum species flower in mid or late summer, and the seed heads are long lasting, often remaining well into the winter. Some Stipa species flower in the spring, the inflorescence standing almost two metres above the clumps of leaves, and again the seed heads last late into the winter.