Torenia isn't difficult to grow and you can start the plant several ways. If you want to get a head start on the growing season, start seeds indoors six to eight weeks before the last average frost date in your area. Otherwise, plant seeds directly in the garden about a week before the last expected frost. If you prefer instant color, purchase bedding plants at a nursery or garden center about two weeks after the last frost. Allow 6 to 8 inches between each plant.
Sun and Soil
Although torenia blooms best in warm temperatures, it doesn't do well in heat and humidity. Plant torenia where it will be protected by shade during hot afternoons or in full, all-day shade if you live in a hot climate. The plant prefers rich, moist, well-drained, slightly acidic soil with a pH between 6.0 and 6.5. Dig 1 to 2 inches of compost into the soil at planting time to improve soil quality and drainage.
Watering
Keep the surface of the soil lightly moist at a depth of 1 to 2 inches until seeds germinate and the plant is established and displays healthy new growth, and then decrease watering. Although torenia prefers moist soil, it is likely to develop rot or fungus in wet, soggy soil. Water the plant to a depth of 6 to 8 inches to be sure the roots are soaked, and then withhold water until the top 1 inch of soil feels slightly dry to the touch. Water at the base of the plant and keep the foliage as dry as possible, because wet foliage invites mold and mildew.
Fertilizer
Regular fertilization provides necessary nutrients to keep torenia blooming throughout the growing season. Water the plant with an all-purpose plant food with a ratio of 10-10-10, 20-20-20 or 5-10-5. Mix the fertilizer at a rate of 1 tablespoon to 1 gallon of water, and repeat every one to two weeks. Water carefully to keep the fertilizer off the leaves, and always apply the fertilizer mixture to damp soil to prevent scorching the roots.