Woody plants that produce a single stem or trunk and many branches are called trees. Woody plants that produce many stems from the soil, with new ones being produced each year, are called shrubs. Plants that produce no woody stems are known as herbaceous. Any plant that lives for many years is a perennial. Those plants that remain in gardens year after year but are not woody are herbaceous perennials. Peonies, iris, and phlox are examples.
Some herbaceous perennials, called bulbous plants, produce bulbs. These include not only the true bulbs, such as tulips and onions, but also the solid bulbs, or conns, such as those the gladiolus and crocus produce. Tubers are produced by dahlias, caladiums, and other tuberous plants. Rhizomes are developed by iris, lily-of-the-valley, and other rhizomatous plants. All of these perennials produce and store food below ground so that a new plant may grow each year.A few plants such as foxglove, Canterbury bells, and wild mullein last only two years. The first year they make a rosette of leaves close to the ground, live over winter, bloom the next year, and then they die. Such plants are called biennials. If seeds are sown each year, there is a constant supply of plants.
Some plants grow from seed each year, bloom, produce seed, and die at the end of the year. These are called annuals. Examples are petunias, marigolds, snapdragons, and zinnias.Everything that grows needs light, air, moisture, and food. From the carbon dioxide of the air the plant, in the presence of sunlight, manufactures sugar. This is soon changed to other substances that make up the main bulk of the plant. Additional plant food comes from the natural minerals in the soil. When the soil lacks minerals, they must be supplied as fertilizer. The food must dissolve in water, so there must be enough moisture.
There are relatively few places on Earth where plants do not grow. If the soil of the garden is not good, it can be improved by digging good soil, manure, or commercial plant food into it. If a plot of ground grows weeds, it is good soil; it will grow desirable plants equally well. Soil without weeds needs to be dug, aired, fed, and enriched with micro-organisms, supplied when manure, garden trash, peat moss, grass clippings, or good compost (peat, leaf mold, and lime mixed) are used.