Gardeners prize pansies (Viola x wittrockiana) for their hardiness and colorful blooms. Though botanically perennials and biennials, pansies are often grown as annuals, and pruning is not required. When done properly, however, this task can help to protect your plants from disease and maximize the flowering show. Pruning recommendations for pansies are applicable for all plants regardless of whether they are grown as annuals, perennials or biennials.

border of pansies
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Cutting back pansies keeps plants compact and clean.

A Cut Above

Pansies have very thin stems, so hand-held bypass pruners or shears are appropriate for trimming. Pruners have smaller blades that work well when less plant material needs to be removed, while shears are longer and more suitable for cutting back more plant growth. The blades should be kept sharp to ensure straight cuts, as opposed to ripping that may occur with dull blades. Ripping the stems creates more wounds and more opportunities for diseases to enter. Diseases can be transmitted from one plant to another through the blades. By wiping down the pruner blades with a solution of 1 part bleach to 9 parts water, the risk of cross-contamination is reduced.

Spent Flowers

Flowers that have wilted and lost their color can be removed from the plant by cutting or pinching the stem of the flower. Flower stems are typically 2 to 3 inches in length and can be trimmed at the base so the cut is covered by the leaves of the plant. This task is done to reduce the risk of disease that can be harbored in plant debris and improve the appearance of the plant. Additionally, it can increase the number of blooms and length of bloom season by preventing the plant from expending energy on setting seeds.

Scraggly Growth

Established pansies can reach a height of 6 to 8 inches and a width of about 8 to 12 inches. Plants started in the spring will likely begin to appear leggy by the end of the season even in proper growing conditions. This term is used to describe plant stems that are elongated, taking away from the plant's attractive display. For pansies grown in hanging baskets, where a greater spread is typically desirable, up to one-third of the plant growth can be cut back. For pansies grown in containers or in the ground, compact, bushy growth is ideal. Remove up to one-half of the plant growth, including flowers, leaves and stems. Use shears and form the plant into a mounded shape. Cutting back the plant in this way will encourage it to branch out more and promote flowering.

Frost Damage

Pansies are tolerant of U.S. Department of Agriculture zones 6 through 10. Though they can survive short bouts of exposure to temperatures below freezing, they may begin to show signs of injury, especially when temperatures drop below 25 degrees Fahrenheit. Frost damage can be diagnosed by withered leaves and/or stems with dark brown or black spots. Symptomatic leaves and stems can be removed from the plant using pruners. This will improve the appearance of the plant while also reducing the risk of insects and disease that thrive in debris.