Kathy Lewis, age 9, of San Francisco, CA for her question:
Does the grass die every year?
The grassy hills around San Francisco are now turning from green to gold. In other places, lawns and meadows have changed from winter brown to green, At certain times, the tawny grass certainly looks lifeless. But no, Kathy the short grass does not die each year. It just waits out a spell of the wrong kind of weather. The short grasses have tricks to cope with droughts, frosts and scorching heat,
Most pastures are mixtures of many kinds of grass. There may be a dozen kinds growing in the lawn. Unless the ground is frozen, the turf is springy to the tread. Meshes of underground runners hold the soil in a spongey carpet. These runners can survive long droughts and bitter frosts, Meanwhile, the leafy blades have ways to protect themselves from hot sun and scorching winds.
The fine white runners have knobby joints, sprouts from these joints can grow up and become leaves or grow down and do the work of roots, The runners are called rootstocks, for they are not true roots, They are really special plant stems,
These rootstocks make the short grasses the molt successful plants in the world. The fine runners bind the plants to windy hillsides. They weave a mesh of spongey turf to hold supplies of moisture and air, Grasses can grow where water is too scarce for trees and shrubs. At one time they covered one fifth of all the land in the world.
When the weather is right, the rootstock sprouts up green shoots, After a warm spring rain pastures may turn from brown to green in a few hours, The leafy blades do not need to live long. Their job is to use air, water and sunshine to make plant sugar. They fight hard to stay as long as they are needed.
The leafy blades have special cells to protect them from the parching air.
Like all plants they are netted with veins. Unlike most plants, they have thin walled cells between the veins, These elastic cells can expand and shrink.
In gentle sunshine, the special cells expand. The grass blades are spread out flat to gather the air and light. In dry, scorching air the special cells shrink. The leafy blades curl up with less surface exposed and less precious moisture can evaporate,
Soon shy little blossoms appear among the green grass, Then come the seeds, The wind blown them away to start new plants in new places. The green leaves have done their work. The rootstocks use them to grow more runners. The grassy turf extends while little seeds are blowing to start more patches of grass elsewhere,