Soap nut husks, as the name implies, can be used as a natural laundry soap, placed directly into the washing machine in much the same way you would add commercial laundry soap. The seeds are also used for shampooing the hair in many Asian countries. Soap nut seeds are available online. It takes a certain amount of effort to sprout a soap nut, but once sprouted the trees grow fairly rapidly, as much as a foot in the first 30 to 60 days. At maturity, the trees can be anywhere from 40 to 60 feet tall. Plants grown in containers can reach heights of 12 feet, depending on how deep the container is; a container which restricts the growth of the tap root will restrict the growth of the tree. Soap nut trees (Sapindus spp.) grow best outdoors in USDA Hardiness Zones 9 through 11.
Remove the hard soap nut seed from its husk. The husks should be saved as they can be used to wash clothes.
Set the soap nut seeds on a hard surface, such as a cement pad, and hit them with a metal hammer. The idea is not to crush the seeds but to merely bruise them and weaken small sections of the seed to encourage germination. This is known as scarifying the seed.
Boil water and then allow it to cool for five minutes. Pour the hot water into a thermos and add the bruised seeds. Close the thermos and allow the seeds to soak overnight in the hot water.
Fill a deep growing pot with potting soil (cut the top off of a 2-liter soda bottle and drill holes in the bottom for water drainage if you do not have a deep growing pot) and place the seeds into the potting soil approximately 1 inch deep. Grow only one seed per growing container, as the trees grow rapidly once sprouted.
Dampen the soil and place the growing pot in a well-lit area, out of direct sunlight. If you live in a warm climate, where the nighttime temperatures do not dip below 60 degrees F, then you can leave your growing pot outdoors. Otherwise keep the pot between 60 and 75 degrees F at all times.
Keep the soil damp but not soggy and be patient. It can take anywhere from one to four months for your seeds to sprout.
Plant outdoors if winter temperatures do not drop below freezing, otherwise keep growing in progressively larger and larger pots. Dig a hole twice as large and deeper than the current root ball so the tap root will be able to grow deeper more easily. Fill in the hole with loose garden soil at the bottom so that the tree can be planted at the same depth as it was in the pot. Press gently around the tree and water well. Keep the ground damp but not soggy.