How to Propagate Black Locust Cuttings
A fast-growing tree native to the eastern and central U.S., black locust (Robinia pseudoacacia) grows up to 80 feet tall. Fragrant white flowers appear on the tree for a short blooming period in spring. The blooms attract bees that turn the sweet nectar into flavorful honey. Propagate black locust by taking root cuttings in late fall or early winter.
Black locust is a tough, cold-tolerant tree that grows in nearly any soil, including poor soil and extremely acidic soil with a pH as low as 2.5. The tree performs best in rocky, sandy soil. Although black locust has few requirements, it does need full sun. The tree requires no fertilizer and is drought-tolerant, requiring little water once established. It grows in U.S. Department of Agriculture plant hardiness zones 4 through 8. The inner bark, young leaves and seeds of the tree are somewhat toxic, so plan carefully if you have small children or pets.
Taking Root Cuttings
A root cutting taken from a dormant tree in late fall or early winter usually develops roots by spring. To take a root cutting, use a garden fork to loosen the soil and uncover a section of roots at the base of the trunk. When you find a long, healthy root with a length of at least 12 inches and a diameter of about 1/2 inch, use the garden fork to loosen the soil under the root. Use a pair of sturdy, sharp pruners to cut the root. Shake excess soil from the root but don't rinse or rub it. Cover the remaining roots back up.
Black locust roots well in a pot filled with moist sand. Cut the stem into 2-inch sections. To remind you which way to plant the cuttings, cut the top of each root section -- the part nearest the tree trunk -- straight across. Cut the bottoms at an angle. Push the cuttings into the moist sand with the top of the cuttings slightly under the surface of the sand. The roots require a cool area where the temperature is consistently between 40 and 50 degrees Fahrenheit.
Potting Rooted Cuttings
The cuttings are ready to plant into 1-gallon pots as soon as new growth emerges from the top of the cuttings in spring. Fill the pots with a well-draining potting mix, such as a combination of equal parts perlite or peat moss and coarse sand. Place the pots in a cool, shady spot. For the best chance of success, let the trees grow to 2 to 3 feet tall. Check the pots often and water as needed to keep the potting soil moist.
- The American Horticultural Society, Plant Propagation; Alan Toogood, Editor
- The New Sunset Western Garden Book; Kathleen Norris Brenzel, Editor
- University of Florida IFAS Extension: Robinia Pseudoacacia, Black Locust
- Fairfax County Public Schools: Black Locust, Robinia Pseudoacacia
- North Carolina State University: Robinia Pseudoacacia