Rhizomes: A rhizome is a modified plant stem which grows horizontally, at or below the soil surface. Rhizomes contain a series of nodes (think of the lines on a bamboo stalk) from which roots and shoots may grow. These modified stems also act as storage organs for the plant (think of a ginger root), where nutrients such as carbohydrates and proteins can be stored, and later used to feed new growth. During the growing season, the nodes on the rhizome give rise to new plants, increasing the density of the lawn, while the tip of the rhizome grows horizontally.
Kentucky bluegrass (Poa pratensis) has rhizomes that are extremely hardy, and are capable of rooting even in compacted soils. These rhizomes produce nodes every few centimetres, which each produce a new plant. This allows Kentucky bluegrass to form dense turf and recover easily from damage. Under extreme conditions such as heat or drought, Kentucky bluegrass will go dormant, and then recover rapidly when conditions improve.
Creeping red fescue (Festuca rubra) is a rhizomatous grass which is especially adept at improving soil stability, and is often used in land reclamation and erosion control, as it is extremely tolerant of flooded or waterlogged soils. Using the nutrients stored in its rhizome, creeping red fescue is able to survive underneath snow cover in order to grow rapidly when the spring thaw begins. This allows creeping red fescue to become established before most perennial weeds.