Orchids can be grown successfully outdoors in the garden like any other flowering perennial plant. They can be found growing naturally all over the United States. The trick is choosing the right kind of orchid to grace your garden with lush foliage and exotic flowers.
Selecting Orchids for the Garden
Garden orchids that are planted in the ground must be terrestrial. Terrestrial orchids grow naturally in leaf litter and debris on the forest floor. Epiphyte orchids can be grown outdoors but not in the ground. Cultivated orchids are generally hardy in U.S. Department of Agriculture plant hardiness zones 2 to 12, but this varies depending on the species. Pink lady slipper orchids (Cypripedium acaule) are terrestrial orchids that are hardy in USDA zones 2 to 8. They bloom in the spring, producing pink blooms with a pouch that resemble a slipper on 1-foot-tall stems. ‘Albostriata’ Chinese ground orchids (Bletilla striata ‘Albostriata’) are hardy in USDA zones 5 to 9. They produce purple flowers in clusters with six to 10 flowers per 1- to 1 1/2-foot-tall stems. Tropical orchids can be grown in the garden, too. Bamboo orchids (Arundina graminifolia) are tropical terrestrial orchids that are hardy in USDA zones 11 to 12. They bloom primarily in the summer but will continue to bloom off and on year round. Their flowers are 2 to 3 inches across with white or pink tepals or top petals and a pink ruffled cup at the center. Cymbidiums (Cymbidium spp.) are tropical orchids that are hardy in USDA zones 10 to 12. Not all Cymbidiums are terrestrial. They are available with blooms in every color except blue or purple. Purchase the orchids from a reputable nursery. Never collect them from the wild.
The soil must drain very quickly for orchids. They will not survive in slow-draining clay soil. Loamy and sandy soil are fine. Regardless of the soil type, dig a 1-foot-wide by 1-foot-deep hole at the intended planting site. Fill it with water. If the water soaks into the surrounding soil within a few hours, it drains quickly enough for orchids. Terrestrial orchids can still be planted outdoors in the garden if the native soil drains too slowly. Construct a 10- to 12-inch high raised bed and fill it with a mixture containing 20 percent loamy soil, 70 percent composted bark mulch and 10 percent perlite or coarse sand.
Choose a planting site with the right sun exposure for the orchids being planted. Some terrestrial orchids like four to eight hours of sunlight each day while others grow best in bright shade. Bamboo orchids prefer four hours of sunlight but grow well with up to eight hours. Cymbidiums prefer bright shade during the summer but want six to eight hours of direct sunlight during the winter.
Soil pH and Organic Matter
Check the soil pH with a soil test kit. Soil sample kits and digital soil test meters are readily available at garden centers. Test the soil at a depth of 2 inches. The surface soil often has a different pH from the soil lower down. Orchids generally grow best in acidic soil with a pH of 6.
If the soil pH is too high, use sphagnum peat moss to lower it. To lower the soil pH by 1, or from 7 to 6, use 2 1/2 pounds of peat moss per square yard. If the soil pH is below 5, use lime to raise it. The amount of lime needed will vary, depending on the soil type. To raise the pH from 4 to 5 in 25 square feet of soil, use 2 1/2 pounds of lime if the soil is sandy or 4.375 pounds if it is loamy. It can take one to two years to raise the soil pH so, if possible, test the soil well ahead of time. The lime should be spread over the soil and mixed in with a shovel or rake to a depth of 6 inches.
Just prior to planting the orchids, spread a 4- to 6-inch depth of composted bark mulch on top of the soil and mix it in to a depth of 6 to 8 inches. Use a rototiller or dirt shovel to mix it thoroughly into the soil. Peat moss can be added at the same time if the pH needs to be lowered.
Plant orchids in the fall six to eight weeks before the first expected frost or in the spring after the last expected frost. They generally need to be planted at a shallow depth. Terrestrial orchids keep most of their roots in the top few inches of soil for better air circulation. If the orchids are potted, plant them at the same depth they were growing in their containers. If their roots are bare, dig the planting hole only 1 to 2 inches deep but wide enough to spread the roots out horizontally across the soil.
Spacing will depend entirely on how large the orchid will get. Cymbidiums range in width from 9 to 36 inches while bamboo orchids grow to a width of 4 to 6 feet. Give each orchid enough room to reach its mature width with 4 to 6 inches to spare. For example, bamboo orchids should be planted 2 1/2 to 3 1/2 feet apart. Water the newly planted orchids generously to settle the soil around their roots.
Spread a 2- to 3-inch depth of shredded bark mulch over the soil to help conserve moisture but keep it away from the orchid stems to prevent injury and disease. Water the orchids when the top of the soil begins to dry. The soil should be kept lightly moist at all times.
- The University of North Carolina Press: Southern Gateways: Native Orchids of the Southern Appalachian Mountains
- Plant Delights Nursery, Inc.: Cypripedium Orchids: Does the Lady Slipper Fit Your Garden?
- Missouri Botanical Garden: Cymbidium (Group)
- Missouri Botanical Garden: Bletilla Striata ‘Albostriata’
- Missouri Botanical Garden: Arundina Graminifolia
- Tucson Botanical Gardens: Orchids: Mad About Orchids
- University of Vermont Extension: Department of Plant and Soil Science: Hardy Orchids
- Sarasota Orchid View Society: Newsletter
- Sonoma State University: Soil pH Preferences of Various Plants
- University of Minnesota Extension: SULIS: Modifying Soil pH
- Photo Credit plusphoto/a.collectionRF/amana images/Getty Images
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