How to Grow a Rain Tree From Seeds
Golden rain tree (Koelreuteria paniculata) is highly ornamental in the home landscape, with clusters of showy yellow flowers in spring and bright yellow foliage in fall. Best grown in shelter from cold winds, it tolerates most kinds of soil and is drought-and pest-resistant. Rain tree reaches a height and spread of 30 to 40 feet during its relatively short life, according to the University of Colorado and you can propagate new rain trees from stem cuttings or seed.
Watch for seed pods to develop in clusters on rain trees in late summer and fall. They resemble small, green Chinese lanterns at first and turn papery and light brown as two or three seeds ripen inside. Collect the ripened pods, break them open and remove the seeds.
Place the seeds and a handful of moist, sterile potting mix in a resealable plastic bag. Put the bagged seeds in your refrigerator for the winter. This process, called cold stratification, imitates outdoor conditions and is necessary for germination.
In early spring, fill a seed tray with moist potting soil. Remove the seeds from the plastic bag and scatter them on top of the soil. Cover them with an additional 1/4-inch of soil and place the seed tray in a warm sunny room. Keep the soil uniformly moist and seeds will germinate in 30 to 60 days if they are viable.
Thin seedlings to 6 to 8 inches apart when they sprout. Fill medium-sized containers with moist potting soil and transplant single seedlings when they develop their second set of leaves. Carry the pots outdoors to an area of partial shade for the summer, watering each time the soil is dry to a depth of 1 inch.
Transplant seedlings to the landscape in early fall. Choose a sheltered area that gets sun for 6 to 8 hours per day. Plant seedlings with the container soil to avoid disturbing developing roots, setting them at least 15 feet apart. Drive plant stakes next to each one to mark their location until they are 2 to 3 feet tall.
Some specimens of rain tree can reach a height of 45 feet, so avoid planting them under power or telephone lines.
Do not fertilize rain tree seedlings in fall. The extra nitrogen will cause a new flush of growth that will die back in winter.