Amstel Series begonias (Begonia x Hiemalis Amstel Series) have a mounding form, typically reaching about 12 inches tall. They usually bloom continuously throughout the growing season. The members of this series belong to the group called Rieger begonias, which were developed by crossing a tuberous begonia with a wax begonia.
Amstel begonias grow as perennials outdoors only in the frost-free climates in U.S. Department of Agriculture plant hardiness zones 10 through 11, but you can treat them as annuals or grow them as houseplants elsewhere.
Where to Plant
Amstel begonias are relatively tolerant of heat and can grow in a variety of light conditions, but do best in a spot that receives sunlight filtered through leaves or that is otherwise partially shaded.
Amstel begonias need consistent moisture, but won't tolerate soggy, saturated soils. Monitor the soil's moisture level carefully, and water so the soil doesn't dry out completely but is never waterlogged. If you're growing your begonias in pots or containers, make sure the containers have drainage holes and are never left sitting in standing water.
Amstel begonias benefit from a monthly application of fertilizer to help them to continue to bloom prolifically through the season. Mix 1/2 teaspoon of water-soluble 15-30-15 fertilizer in 1 gallon of water, and use the solution to water the plant. Apply it at the base of the plant, and avoid getting the fertilizer on the plant's leaves and stems.
Over the course of the season, Amstel begonias may get leggy or have a ragged in appearance. If this happens, prune or pinch the stems back so that they contain three to five growth nodes. The plants will rebound from this severe pruning and should start to bloom again in a week or two.
Removing wilted flowers promptly will encourage the plant to put its energy into new flowers and will help ensure it keeps blooming vigorously.
If you use pruners to maintain the plant, dip the blades in isopropyl alcohol after each cut to help prevent the spread of diseases.
Pests and Diseases
Amstel begonias are resistant to most pests and diseases and should be problem-free given good growing conditions. To prevent fungal infections, such as powdery mildew, avoid getting the leaves wet when you're watering and space the plants 12 to 15 inches apart so that there is plenty air circulation around the plants.