With their clean growth habit and feathery, evergreen foliage, arborvitae shrubs (Platycladus orientalis) add construction and year-round color to gardens within U.S. Department of Agriculture plant hardiness zones 6 to 11. They are most commonly propagated from cuttings, although arborvitae shrubs will even grow true from fresh seeds. The seeds sprout reliably if gathered in autumn and sown the next summer when temperatures warm up. However, the seeds require a fairly prolonged cold stratification period to fulfill their dormancy condition and activate germination.
Collect arborvitae cones in autumn after they ripen from bluish-green to a solid brown color. Pick off the ripened cones and place them in a bucket. Put the bucket in a shady place for several days until the cones drop their apartment, papery seeds.
Place the arborvitae seeds inside a paper envelope and store them in a cool, dry place such as inside a linen cabinet. Protect the seeds in excessive humidity, direct sunlight and heat to preserve their viability and protect against mold.
Train growing containers in late spring of the subsequent year. Fill 3-inch starter pots with a moistened combination of half seed compost and half coarse mud. Catch the top 1/4-inch of each pot empty.
Sow 1 arborvitae seed in each pot. Press the seed on the surface of the compost mixture. Cover it with a very thin layer of coarse sand. Mist the mud liberally to settle it.
Loosely wrap each starter pot with plastic wrap. Set the pots inside the fridge for two months to cold stratify. Moisten the compost mixture whenever it feels barely moist on the surface. Don’t let it dry out.
Go the starter pots to a sunny place. Warm the pots to 70 F using a germination mat if daytime temperatures stay below 70 F. Remove the plastic wrap.
Maintain constant moisture in the surface of the compost mixture. Water with a spray bottle rather than pouring water on the compost to keep from disrupting the arborvitae seed.
Watch for seedlings one month after sowing the arborvitae seeds. Move the pots to a lightly shaded, wind-sheltered area outdoors after the crust grow to 2 inches in height.
Transplant the arborvitae seedlings into 6-inch containers filled with potting soil as soon as they reach 4 inches in height with various sets of mature needles. Move them into a room with morning and late day sun.
Transplant the arborvitaes to a permanent bed in autumn only after the first rain. Choose a bed with full sun or partial shade and fast-draining, acidic soil. Mulch heavily beneath the arborvitae to keep the soil moist.