All grasses are broadly divided into three main categories - annually growing grasses, biennially growing grasses and perennially growing grasses. The annual grasses exist for a full year, living for their entire life span. They are propagated from their seeds, and have leaves, roots, and stems and also bear flowers. They pass away in one season. The majority of the grasses that form our staple food are from the annual variety. On many occasions, the annually growing ornamental grasses go unnoticed. However, several of them are genuinely attractive and can be grown without any difficulty.
Even the biennially growing grasses are propagated from their seeds and their growth continues throughout the season. They grow throughout the winter and maintain the growth during the following season, when they blossom and eventually wither away.
On the other hand, perennially growing grasses survive and keep growing for over two consecutive seasons. In fact, most of the significant and eye-catching ornamental grasses belong to the perennial category. Several species of perennial grasses live for an extremely long period, often persevering for a few decades! Such ornamental grasses may also be herb-like, timbered or semi-woody. In effect, the major collection of woody grasses is also the biggest group of genuine grasses - the bamboos.
Another interesting thing about grasses is that while some of them are annual in one climatic condition, the same grasses are perennial when grown in a different climatic condition. For instance, while the tender fountain grass (botanical name Pennisetum setaceum) is a perennial grass when grown in the placid Mediterranean climate prevailing in South California, it is regarded to be an annual variety when grown in the Pacific Northwest. In addition, every variety of grass has different levels of acceptance of heat and cold and also responds dissimilarly in different climatic conditions. Time and again, a very small distance like 20 miles may even cause a difference in the climatic condition wherein a specific grass may just be regarded as an annual variety, from another climatic condition where the same species may considered to be perennial.
All species of ornamental grasses are broadly categorized into two groups - warm season grass and cold season grass, conditional on the time of the year when their growth is robust. Precisely speaking, the growth of warm season species is most active when the temperatures start rising during the spring. Grasses belonging to this category blossom as well as produce seeds during the summer and in the fall, following which they turn out to be inactive with the commencement of winter. On the other hand, the cool season grass species have their active growth period during the later part of winter or during the beginning of spring. They bear flowers during the period between winter and the beginning of summer, and subsequently turn out to be latent or their growth slows down during summer. The active growth of the cool season species begins again when the temperatures start declining in fall. In places where the winters are mild, these grasses keep growing throughout the winter months.
It is worth mentioning here that the tendency of seasonal growth of the grasses is habitually associated with the climatic condition where they have their origin. For example, grass species that are indigenous to regions having arid summer conditions, generally turn out to be inactive when the weather is hot and continues active growth when the temperatures begin to fall and with the onset of rainfall. On the other hand, grass species that have their origin in regions having cold winters, usually become dormant during the fall. These grasses resume their active growth when the temperatures begin to rise during spring.
Such recurring prototypes may also change, conditional on the diverse climates as well as situations. When the conditions are normal, the cool season ornamental grass will lie dormant during the summer - which is considered to be an intrinsic protection in the face of drought. However, if you keep on watering the plants on a regular basis, it is possible that some of them will sustain their growth even in such conditions.
There are basically two different forms of growth patterns that distinguish the grasses. While the running grasses multiply by means of their crawling stems, thereby forming thick mats, many of this species may also turn out to be invasive. An example of the second type of growth is the clumping grasses that develop in bunch, gradually enhancing in width. Both these types have equal status and presence in the gardens.
The structure of grasses varies, and they are found in various different forms and dimensions. Basically, there are six main types that are used to describe the forms of grasses. These classifications illustrate the shape of the foliage and do not apply to the inflorescences or the flowering stems irrespective of the tallness of the plant. The different categories of grass form are described in brief below.