With minimal care, pansies (Viola x wittrockiana) that are grown in containers bloom abundantly, offering their colorful flowers before most plants start budding. Use them to fill window boxes and patio planters, or grow them in pots on a porch or entryway. Pansies are often grown as annuals and bienniels, but they are actually short-lived perennials (http://aggie-horticulture.tamu.edu/wildseed/growing/annual.html) in U.S. Department of Agriculture plant hardiness zones 6 through 10.
Encouraging More Flowers
Pluck off potted pansies' dead and fading flowers once each week. Locate the spot directly under such a flower, and gently pinch it from its stalk by using a small pair of disinfected clippers or your fingernails. The removal of spent flowers, a practice called deadheading, encourages more flowers by preventing plants from pouring energy into seed production.
Wash your hands with soap and water before and after deadheading to prevent the potential spread of plant diseases in your garden.
If you use clippers, then disinfect the cutting blades before and after deadheading by using a mild bleach solution; 1 part regular household bleach to 3 parts water is sufficient. Soak the blades for five minutes to allow the solution to kill pathogens, and then rinse the tool with plain water. Let the clippers air-dry with the blades in the open position.
Watering and Fertilizing
Water your potted pansies when the top 1 inch of their potting soil feels dry to the touch. Pansies do best in consistently moist soil and wilt if allowed to dry out completely. Also avoid wet, waterlogged soil, which suffocates the roots, potentially causing pansies to droop.
Ensure each pot, planter or window box containing pansies has holes in its bottom for drainage.
Potted pansies require bimonthly fertilizer to bloom well. Mix 1 teaspoon of a liquid, all-purpose plant food concentrate, such as a 12-4-8 formula, with 1 gallon of water. Every two weeks, use the diluted fertilizer in place of plain water to water the pansies' soil.
Managing Leaf-Eating Pests
Check the pots, planters and window boxes for slugs and snails, which feed on pansies' tender leaves and flowers. Pick those pests off the plants, and destroy them. Slugs and snails tend to appear during damp weather. So check for them after a rain. If you see holes in your pansies but cannot locate the culprits, then use a flashlight to check the plants after dark because slugs often feed at night. Other than slugs and snails, pansies rarely suffer pest problems.
Understanding Heat and Summer Burnout
Temperature plays a role in potted pansy care. Pansies thrive when evening temperatures are between 40 and 65 degrees Fahrenheit. They tolerate slightly higher daytime temperatures, up to 75 F. When the weather is hot, however, no amount of watering or shade keeps them from burning out, wilting and drooping. In locations with mild winters and hot summers, pansies can be grown from fall through early spring. In areas with hot summers and cold winters, they thrive in spring and fall.
Avoid having scorched pansies in summer by replacing them when they start to wilt from heat, using more heat-tolerant flowering plants then.
Identifying and Managing Leaf Spots
Caring for potted pansies occasionally requires dealing with pansy leaf spots. The spots on leaves are symptoms of fungal infections and are black or tan and may look greasy.
When shopping for plants, check them for leaf spots to avoid introducing a fungal infection to your plants. As you water your pansies, concentrate the water spray on the soil to keep the leaves dry. Use new potting soil rather than recycling last year's soil when planting, and wash plant pots with hot water and soap at the end of each growing season.
Discard your pansies that show fungal leaf spot symptoms, and replace them with healthy plants.