Colorful annual or perennial impatiens (Impatiens spp.) are best known for their ability to brighten up shady spots. The perennial types grow in the warm climates of U.S. Department of Agriculture plant hardiness zones 10 through 11, but you can grow them as annuals elsewhere. They mostly bloom in summer, with some varieties flowering into spring and fall. Several issues could cause impatiens to stop blooming.
Downy mildew affects most varieties of impatiens with the exception of New Guinea impatiens (Impatiens x hawkeri). This disease is most prevalent in areas with cool nighttime temperatures and high humidity. It can cause plants to have stunted growth, yellowing and downward-curled leaves. If your impatiens have downy mildew, you may notice a white fuzzy layer underneath the leaves. This disease can affect blooming as the flowers and leaves commonly fall from the plant.
Crowding your impatiens can lead to few or no blooms. New Guinea impatiens can reach 18 to 36 inches tall with a spread of 24 to 36 inches. If you don't give the plants enough space, they will compete for water, nutrients and light. Crowded plants means the lower leaves can't photosynthesize. These factors can reduce the number of blooms on your plants. Space your New Guinea impatiens far enough apart so the leaves will not overlap when the plants reach their mature size.
Impatiens need regular water for optimal bloom. Too much or too little moisture can cause damage to the plant and stop it from producing flowers. If your impatiens dry out and begin to wilt, they will likely drop their leaves and flowers. With too much water, the soil becomes over-saturated and the roots will rot because they're deprived of oxygen. This will also cause blooming to stop.
Although impatiens have been hybridized to tolerate more sun than the original varieties, too much sun can reduce blooming. Shade-loving varieties of impatiens should be planted in an area where they will receive less than six hours of direct sun per day. Signs that your impatiens may be getting too much sun include stunted growth and few blooms.