A Tropical Landscape With Boston Ferns & Calla Lilies

Boston ferns (Nephrolepis exaltata "Bostonensis"), white calla lilies (Zantedeschia aethiopica) and calla lily hybrids (Zantedeschia hybrida) are tropical plants. They can be planted outdoors, though, to create a tropical landscape in any climate. Boston ferns grow in U.S. Department of Agriculture plant hardiness zones 9 through 11, while calla lilies grow in USDA zones 8 or 9 through 11. In these warmer climates, they grow outside year-round, but in cooler climates, you'll need to do extra work to keep them alive.

White calla lilies can be grown in full sun to bright shade. Calla lilies that produce bi-color, pink, purple or yellow flowers are hybrids and grow and flower best in full sun to partial shade. Boston ferns cannot be grown successfully in full sun -- they require partial to full shade. A foundation planting along the east side of a house is fine for calla lilies as well as Boston ferns. They will get cool direct morning sun there with shade in the afternoon and evening. A landscaped area below tall trees with bright or dappled shade is also a good spot. Calla lily hybrids may not thrive in the lower light levels but they will grow and bloom.

Test the soil's pH three to six months before planting the Boston ferns and calla lilies. The soil needs to be acidic with a pH of around 6. Mix sulfur into the soil to lower the pH. The rate of application depends on how much the pH must be changed and the type of soil at the planting site, but may be around 1/10 pound sulfur for every 10 square feet to decrease the pH by 0.5 points. Heavy clay soil requires more sulfur to lower the pH. The soil should also be rich in organic matter. Mix peat, leaf mold, compost or well-aged manure into the soil before planting.

Boston ferns and white calla lilies grow to a height and width of 2 to 3 feet. Hybrid calla lilies come in a variety of sizes. "Rubylite Pink Ice" (Zantedeschia "Rubylite Pink Ice"), for example, grows to a height of 12 to 18 inches and width of 6 to 12 inches. Boston ferns and larger calla lilies should be planted 18 inches apart. Smaller hybrid calla lilies can be planted 12 inches apart, but when planted next to Boston ferns and larger calla lilies, they should be planted 18 inches apart to allow for the mature size of the larger plants. Plant them in spring when there is no longer any danger of frost. Spread 2 to 3 inches of organic mulch around them to help retain moisture and water them as often as necessary to maintain uniformly moist soil. The soil should be moist, not soggy.

Boston ferns and calla lilies need humid conditions to thrive and look their best. In dry climates, consider incorporating a water feature in the tropical landscape. A larger water feature might include a waterfall and flat stone shelves to set the plants on. For a smaller water feature, sink a large pan, such as an old sugar kettle, or preformed pond, into the soil and fill it with water to provide added interest and increased humidity. Arrange the Boston ferns and calla lilies around the pool. Species calla lilies can be grown in 1-foot-deep water.

In cold climates, Boston ferns and calla lilies can be sunk into the soil in their containers for easy lifting in fall. Use a fast-draining, peat-based potting mix to plant the Boston ferns and calla lilies in containers. Remove catch saucers from the bottoms of the containers. The planting holes must be large enough to hold the entire container with the top rim at ground level. Spread mulch over the tops of the containers to hide them. In fall, when temperatures begin to dip below 50 degrees Fahrenheit, lift the containers and take them into the house.