Herbaceous ornamental plants include annuals, biennials and perennials. Herbaceous plants have green stems that are usually soft. During the winter the plant dies back to the ground and regrows from the root crown in the spring. These plants are best identified by their flowers, which tend to be bright in color and quite distinguishable. The shape and arrangement of leaves may also help with identification.
The best way to identify a herbaceous ornamental is to wait for the plant's bloom and then use a plant guide to confirm the identification. The "Manual of Herbaceous Ornamental Plants" by Steven M. Still, for example, helps you with plant identification. Most comprehensive plant guides include full color photos of herbaceous ornamental plants.
Monocots and Dicots
You can narrow your identification search by plant family in some cases if you know whether your plant is a monocot or dicot. Observe the plant growth from the planting of its seed. Monocots have one leaf upon emerging from seed. Dicots have two. These original leaves are called embryonic leaves. Many vegetables and annuals are started from seed, and embryonic leaves are visible once they emerge above the soil.
Take note of not only the flower color of your herbaceous ornamental plants, but also how the flowers are arranged on the stem. Campanulas, for example, bloom in a variety of colors but have a common bell-shaped flowers that stack one on top of the other on the stem. Peonies, another herbaceous ornamental, also come in a variety of colors but are identified by tight, ball-shaped buds that open into flowers with multiple layers of petals.
Many herbs are herbaceous ornamental plants. Herbs often do not bloom until late in the season, which means you may have to rely on leaf identification, root structure and even smell to identify the plant. Plants in the mint family, for example, spread via an extensive, knotty root system. Picking a leaf and crushing it between your fingers releases a distinct mint smell.
If you are not certain whether a plant in your garden is a herbaceous ornamental, watch it grow for a season. Note the color and arrangement of the flowers. Also note the structure of the leaves and root system. In the fall, watch for the plant to drop blooms and then gradually die back to the ground. If this happens, you likely have a herbaceous ornamental. Annual herbaceous plants sometimes reseed themselves if you do not pull them from the garden too early. Biennials and perennials die back and then regrow from their root crown the next season.