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Browallia is a genus of flowering plants in the Solanaceae family. This group is also known as the nightshade family — which includes many toxic plants — but also features such edible plants as tomatoes and potatoes. Several species of Browallia are grown for their blue, purple, or white flowers. The plants are perennials in warmer climates, but are usually grown as annuals elsewhere. They grow well in the shade, and are frequently used as a color source in mass plantings or hanging baskets.
The primary species grown is Browallia speciosa, also known as amethyst flower or bush violet. Often the species is not delineated and is just referred to as Browallia. Amethyst flower grows to between 1 to 3 ft (0.3 to 0.9 m) tall, with 1.5 to 2 inch (3.75 to 5 cm) flowers, from the spring through the fall. As the plants grow, they should be repeatedly pinched back to encourage bushiness and greater flowering.
Browallia is grown around the world, including most of the continental United States and Alaska. The plants prefer afternoon shade. Amethyst flowers will grow in a variety of soils, but they prefer one that is rich and well-drained. It is best to keep the soil moist. Too much watering or fertilizer will result in plants that produce an excess of leaves and very few flowers.
Frequently, amethyst flowers are grown from seed. These should not be covered with soil, as they require light to germinate. They also require warm temperatures, ranging from 70-75°F (21.1-23.9°C). The process of germination takes two to three weeks, and the seeds should be planted at least 12 weeks before they are to be planted in the garden. Before the plants can be planted outside, they should be gradually acclimatized to colder temperatures in a process known as hardening-off.
The plants should be planted at ten-inch (25 cm) intervals. In very cold climates, it is better to plant bedding plants than to plant seedlings. By the time seedlings grow to maturity in this type of climate, the gardening season is almost over. In warmer climates, amethyst flower will grow as a perennial. If the plants are being treated as an annual in such climates, the seeds should be planted in the fall for winter flowering.
Browallia is also grown as a houseplant. In the winter, it should receive four hours of morning sun, and no direct sun during the rest of the year. Ideal temperatures at night are between 55 and 60°F (12.8 to 15.6°C) and 68 to 72°F (20 to 22.2°C) during the day. The plants should be fertilized every month in the winter, and every two weeks the rest of the year.