How to Sprout a Hackberry Seed
Sometimes called nettle tree, the common hackberry (Celtis occidentalis) is a deciduous tree valued for its umbrella-shaped canopy and attractive fall foliage. It grows in U.S. Department of Agriculture plant hardiness zones 2 to 9, where it will grow in urban, seaside and rural landscapes with equal vigor. Common hackberry trees propagate best from seeds, which you gather in fall as soon as they ripen. The seeds sprout quickly if kept moist, warm conditions after their initial treatments.
Gather hackberry fruit in late summer or early fall, as soon as they ripen to a solid, purplish-red color. Choose berries with unblemished flesh and avoid those with insect holes or other signs of damage.
Place the hackberry fruits in a bucket. Gently crush the flesh using a soft mallet to make the seeds easier to extract. Cover the seeds with water and soak them overnight, stirring the water occasionally.
Scoop out and discard the fruit flesh and rotten seeds that float to the surface of the water. Drain off the remaining water. Pick through the seeds at the bottom of the bucket and discard any with obvious signs of damage.
Rub each hackberry seed with a fine rasp to weaken the seed coat. Apply very light pressure when scarifying the seed, and rub only until a pale spot develops. Do not make a hole in the seed coat.
Fill 3-inch starter pots with a mix of 3 parts coarse sand and 1 part seed compost. Drizzle water onto the sand mix until it feels very moist in the top half.
Poke a 1/2-inch-deep hole in the center of the sand mixture and place one hackberry seed in each pot. Cover the seed loosely with the sand and compost mixture. Mist the mixture to settle it.
Wrap the starter pots with plastic wrap. Place the pots in the refrigerator or outdoors against a north-facing wall. Chill them for three months to cold-stratify the seeds. Remoisten the sand mixture whenever it dries out in the top 1/4 inch.
Move the pots into a cold frame or indoors near a large window. Remove the plastic wrap. Set the pots on a germination mat and cover them with a plastic propagation dome or a sheet of plastic wrap. Adjust the temperature on the germination mat to between 75 and 80 degrees Fahrenheit.
Water the hackberry seeds whenever the sand mixture feels mostly dry just beneath the surface. Avoid over-watering them to avoid mold and fungi problems.
Watch for sprouting in approximately three months. Keep the hackberry seedlings on the germination mat for another two weeks to encourage growth. Transplant them into 6-inch pots filled with standard potting soil once they reach 2 inches tall.
Move the hackberry seedlings to a lightly shaded area of the garden in spring after the last frost. Grow them under dappled shade with periodic watering for their first summer. Transplant them into a garden bed in fall, just after the first rain.
- Fine rasp
- 3-inch starter pots
- Coarse sand
- Seed compost
- Spray bottle
- Plastic wrap
- Germination mat
- Propagation dome
- 6-inch pot
- Potting soil
- California Polytechnic State University Urban Forest Ecosystems Institute: Common Hackberry
- Colorado State University Forest Service: Growing Trees and Shrubs from Seed
- University of Florida Department of Environmental Horticulture: Landscape Plant Propagation Information: Celtis Occidentalis
- University of California Alameda County Master Gardeners: Your Alameda County Garden Month-by-Month