Apply a balanced slow-release fertilizer to the garden bed prior to planting. Apply the fertilizer at the package-recommended rate. Begin fertilizing container-grown impatiens two weeks after planting by applying a soluble, flowering-plant fertilizer every two weeks at the recommended rate.
Spread 2 inches of mulch over the bed but avoid covering the base of the impatiens with the mulch. The mulch helps keep the roots cool and retains moisture in the soil.
Water the impatiens one to two times a week or when the top half-inch of soil feels dry. Irrigate in the mornings so the foliage has time to dry before the cooler evening temperatures. Provide enough water to moisten the top 6 inches of soil.
Pinch back the plants once they are 6- to 8-inches tall if they appear sparse or leggy. Break off the top ¼ inch of each stem. Pinching encourages the stem to branch and grow in most lushly. Impatiens rarely require pinching once established.