Robinia pseudoacacia, commonly called black locust, is medium sized deciduous tree that typically grows to 30-50’ (less frequently to 80’) tall. It is native to the Allegheny Mountains in the west-central Appalachian Mountains. It will grow as a broadly columnar single trunk tree with a narrow oblong crown. It is noted for its attractive compound leaves and pendant racemes of pea-like flowers. Branches are usually armed with short paired spines (to 1.25” long). Pinnate dark blue-green leaves, with each leaf having up to 23 lance-shaped to ovate leaflets. Leaves turn uneventful yellow in fall. Fragrant wisteria-like white flowers in pendant racemes (to 8” long) bloom in late spring. Bees are attracted to the flowers. Flowers are followed by smooth, flat, purple-brown seed pods (to 4-5” long). This species is also commonly called common locust, yellow locust, white locust, green locust, pea flower locust and false acacia. Grow in average, dry to medium, well-drained soils in full sun. Tolerates some light shade, but avoid shady locations. Tolerates a wide range of soils including sandy or nearly barren ones. Best performance is in moist, organically rich loams. Good drought tolerance. Fixes nitrogen. Black locust is generally considered to be a very easy-to-grow tree. It thrives in many difficult growing conditions.
The seeds have a hard seed coat that has to be treated, or scarified, in order for water to enter the seeds so that they can sprout.
- Scarify the seeds by nicking or sanding the seed coat. The seeds can be sanded with sandpaper, a nail file or an emery board.
- Soak the seed in water for 12-24 hours.
- The seeds like moist, well-drained soil. Prepare a mixture of half potting soil and half sand, perlite or vermiculite. Put the soil in a pot. Water the mixture so that it is moist but not wet.
- Put the seeds on the soil.
- Cover the seeds with a layer of soil.
- Water the seeds.
- Place the pots in an area in full sun or part shade. The seeds should germinate in a few weeks.
- When the seedlings are a few inches tall, they can be transplanted.