How to Germinate a Horse Chestnut
With its spreading canopy and fragrant flower clusters, California horse chestnut (Aesculus californica), also called California buckeye, adds summertime shade and ornamental appeal to low-water landscaping. It grows best within U.S. Department of Agriculture plant hardiness zones 7 and 8, where it reaches a mature height of 10 to 20 feet with a 20- to 30-foot spread. California horse chestnut seeds germinate reliably if kept under moist conditions, providing a reliable means of at-home propagation. However, they must first be hulled and treated with bleach to prevent rot and eliminate parasites.
Put on rubber gloves before working with horse chestnuts since they contain toxic saponins and will irritate the skin of sensitive individuals. Wear long sleeves, as well, to further limit your contact with the seeds.
Remove the spiny husks from the horse chestnuts. Carefully press the blade of a paring knife onto the husk until it penetrates. Score around the husk until it is cut in half. Peel off the two halves and discard them.
Place the hulled horse chestnuts in a bucket of water. Soak them for 24 hours to soften the inner hull. Drain off the water the next day and lay the seeds on a flat surface to drain.
Place the horse chestnuts in the bucket. Pour 5-percent bleach into the bucket until the seeds are barely covered. Soak them for one minute. Remove the seeds and rinse them thoroughly. Discard the bleach.
Fill the bottom one-third of a sealable plastic bag with moistened perlite. Place the horse chestnuts in the bag. Add more moistened perlite until the horse chestnuts are completely covered. Seal the bag.
Store the horse chestnuts inside the refrigerator for six to eight weeks. Remoisten the perlite with a spray bottle whenever necessary to maintain a constant level of light moisture. Do not let the perlite dry out completely.
Prepare planting containers just before removing the horse chestnuts from the refrigerator. Fill 6-inch nursery containers with a moistened mixture of equal parts milled peat moss, shredded pine bark, perlite and coarse sand.
Sow one horse chestnut in each container. Dig a planting hole with a depth equal to the diameter of the seed, or approximately 1.5 to 2 inches. Place the seed in the hole and cover it completely.
Place the planting containers outdoors under partial shade. Maintain a moderate level of moisture in the top 2 inches of soil. Allow the surface to dry between waterings.
Watch for germination three weeks after planting. Decrease watering after germination so the top 1/2 inch of soil dries out between waterings. Avoid overwatering at this point since the seedlings will develop poorly.
Transplant the young horse chestnut seedlings into a permanent bed with acidic soil once they grow to 4 inches in height and have several sets of leaves.
About the Author
Anastasia Leon began writing professionally in 2001. Her experience as a horticulturalist and nurseryman informs her work, which has appeared in publications such as Mother Earth News and Modern Farmer. Leon is a certified master gardener and holds a Bachelor of Arts from the University of California, Santa Cruz.