Massachusetts consists of USDA plant hardiness zones 4 to 7, and most begonias need a warmer climate to grow as perennials. Fortunately, some hardy begonias (Begonia grandis) will survive the winter Massachusetts months in zones 6 to 7. Other popular begonias include wax, tuberous, rex and dragon wing, and they will grow as annuals in Massachusetts. No matter which variety you choose, plant your begonias in the spring after the last frost and when the ground is workable again.
Select begonias that are winter hardy in your area if you want them to grow as perennials. Begonias not rated to your climate are considered tender and will grow as annuals.
Pick a spot to plant your begonias. Most begonias prefer partial shade. However, some varieties, such as wax begonias, also grow well in full sun, and other varieties, such as the hardy begonia, grow well in full shade.
Turn over the soil to a depth of about 12 inches and mix in about 3 or 4 inches of compost, leaf mold, peat moss or another similar organic matter to create a planting bed that is rich in organic matter. It will also help improve water drainage.
Plant your begonias to the same depth as they were planted in their nursery containers. Space multiple begonias according to their label. As a guide, most begonias are spaced about 12 inches apart.
Water your begonias after planting with about 1 inch of water. Continue to water them with about 1 inch of water a week when rain is scarce. During the hot summer months, water them two or three times a week.
Mulch the begonias that are hardy in the fall to protect them through the cold winter months. Spread about 3 or 4 inches of organic mulch such as wood chips, straw or bark.