Grass Plant Growth and its Relationship to Lawncare
A lawn is an area of land covered by many individual turfgrass plants. In fact, a lawn may be considered a garden area comprised of many individual grass plants rather than just a few flower or vegetable plants. It has been reported that in a typical 1,000 square feet of lawn there are about 1 million grass plants.
The first step in any lawn care plan should be to provide an ideal environment for growth and function of grass plants. A healthy, vigorous lawn is the best defense against attack or invasion of various pests. Also, a healthy lawn is much more capable of quickly recovering from modest damage caused by insects, diseases, or physical wear and tear.
Creating a healthy lawn environment is like any other type of gardening. The same good practices used in vegetable and flower gardens are just as appropriate for growing grass plants. The means to achieve those conditions are somewhat different for lawns than gardens, but are just as important for healthy grass plants as for healthy tomatoes.
As with other garden plants, knowledge about the plant and how it grows is often the key to successful growing. Large juicy tomatoes, fresh crisp lettuce, and colorful marigolds are the result of applying knowledge about those plants to growing them in the garden. Likewise, similar knowledge about the grass plant will be very helpful in successfully growing it and creating a healthy attractive lawn.
Grass Plant Structure and Growth
The major grass parts are shown in Fig. 1. The part of the grass plant familiar to most people is the leaf. The leaf is composed of two parts: the leaf blade and the leaf sheath. Looking at the grass plant closely will reveal that the leaf rolls itself around the stem (or shoot) forming the leaf sheath.
The leaves, stems, and roots all originate from the crown area of the plant. The crown is a very tightly compressed stem or growing point that pushes the new leaves upward as they are formed and grow. This is a different growth habit than found in other garden plants such as tomatoes, marigolds, trees, and shrubs. In those instances, the outward growth extends from the tips of the branches or shoots. The location of the grass crown near the base of the plant and usually at, or slightly below, the soil line allows us to mow our lawns regularly and have continued growth.
A common growth characteristic of grass plants is their ability to spread out from a parent plant. Growth habit describes the type of shoot growth present in particular grass plants and is directly related to their ability to spread out from the parent plant and ultimately form a lawn. There are three general classifications of growth habit present in grasses: bunch-type, stoloniferous, and rhizomatous. The specific type of growth habit along with the rate of shoot growth will determine how quickly and easily these grasses will establish a lawn area or fill in bare spots.
Figure 2
Bunch-type grasses spread primarily or entirely by the production of tillers. As illustrated in Fig. 2, tillers originate from the crown area and grow upward from the base of the plant. It is this type of continuous shoot production by means of tillers that gives the plant a clumpy appearance; hence the name bunch-type grass (Fig.2). Seeding rates need to be higher when bunch-type grasses are a significant portion of the seed mixture or blend. When seeding rates are too low or where growth develops from individual isolated plants, small clumps are formed creating a non-uniform lawn surface. Common cool season lawn grasses associated with this type of growth habit are perennial ryegrass, tall fescue, hard fescue, and chewings fescue.
Stoloniferous grasses spread by lateral stems, called stolons, that creep over the ground and give rise to new shoots periodically along the length of the stolon (Fig.2). Lawns formed from these type of grasses appear to have their aerial shoots growing laterally along the ground rather than upright as in bunch or rhizomatous grasses. Creeping bentgrass is a good example of this type of growth. When it is mowed at heights greater than 3/4 inch, it forms a relatively loose mat of grass with most aerial shoots growing horizontally. In bluegrass lawns, creeping bentgrass is usually considered a weed. Creeping bentgrass is considered very desirable on putting greens, croquet courts and other fine turf areas as it will adapt to very low mowing heights (i.e., about 1/4 inch or slightly less) and create a very smooth playing surface.
Rhizomatous grasses spread below ground stems known as rhizomes (Fig. 2). These rhizomes terminate in a shoot that emerges some distance from the mother plant. As these new shoots mature they will also produce rhizomes that eventually produce new shoots thus creating a lawn. Healthy, vigorous rhizome type grasses such as Kentucky bluegrass tend to form dense, uniform lawns with shoots oriented in an upright position.
Root growth also originates at the crown. However, roots continue to lengthen and grow from the root tip as opposed to the growth of shoots and leaves which are pushed upward and outward from the crown at the base of the plant. Roots are naturally sloughed-off and new ones regrow as a normal part of grass plant growth. Also, adverse environmental conditions can significantly shorten the life of grass plant roots. For example, weather and soil stresses associated with drought conditions or excessive rainfall can cause significant root injury or loss and inhibit growth.
Growth Cycle of a Cool Season Grass Plant
Grasses grown for turf use in Minnesota and other north central states are known as cool season grasses. Turfgrasses adapted to the southern states are known as warm season grasses. Fig. 3 illustrates the general growth cycle differences between these two grass types. Note that the cool season grasses have growth peaks in the spring and fall, indicating a response to the cooler conditions at those times of the year. The warm season grasses have a peak growth period during the summer months, providing ample water is present, indicating their response to the warmer conditions. Annual weedy grasses, such as crabgrass and foxtail, also follow the warm season growth curve. In the case of crabgrass or foxtail, they begin their life cycle from seed while perennial warm season grasses, such as bermuda grass, begin growth from existing plant structures.
During the short days and cool temperatures of late fall, mature shoots of cool season grasses go through a permanent biological change. That is, the shoots cease to produce just leaves and sheaths and "switch" over to shoots, which will produce flowering shoots during the long days and warm temperatures of late May through June. Most of the shoot growth that occurs during spring is the production of flowering stems. However, since regular mowing is being done during this period, flowering stems often go unnoticed in home lawns.
Occasionally, questions are raised about the presence of an "undesirable" grass in the lawn during this spring time period. However, people are usually noticing the flowering stems actually blooming on the cool season grasses especially if their mowing heights are quite high. These flowering stems are quite tough and coarser in texture compared to the grass leaf blades.
Once the grass shoot has completed its flowering cycle, it dies along with its associated roots. Since these dead shoots are continually being replaced by new ones and those which were not mature enough to flower, there is little detectable difference in the lawn. It may just appear somewhat thinner by the end of June or early July. Rejuvenation of the grass plant begins again in late July or early August and the process starts over.
In our cool season grasses, most root initiation and growth occurs in the spring with a smaller peak of growth during the cool weather of fall. For a comparison of root and shoot growth patterns see Fig. 4. Notice that root growth begins and peaks in activity before peak shoot growth activity in the spring. While there is some shoot growth activity during the summer months, providing that the grass plant is not in summer dormancy, root growth is very slow. Finally, there is another peak period of root growth lagging slightly behind the late summer shoot growth period. It should be noted from the chart that maximum root growth and shoot growth do not occur at the same time. In fact, they may be considered somewhat antagonistic to each other. Adjusting turf management practices to optimize growth of either roots or shoots is a significant factor in establishing and maintaining a healthy turf.
For more information on grass plant growth, see: