How to Grow Aspen Trees in California
Rake out and replace mulch annually to keep weeds suppressed and soil temperature regulated.
Avoid planting aspen near septic systems and sidewalks, because its roots are deep and invasive.
Quaking aspen (Populus tremuloides) is a fast-growing, short-lived deciduous tree that can quickly reach a height and spread of 40 feet. Aspen is native to the west and east coasts of the United States, according to the University of Connecticut, and is hardy to USDA hardiness zones 1 to 7, which includes most parts of central eastern California. Plant it wherever you have full sun and moist, well-drained soil, preferably near water.
Choose a planting site for aspen that gets full sun for at least six to eight hours per day. In most areas of California, this is not difficult to do. The southeast area of a yard is ideal.
Plant aspens in fall. Dig a hole with a shovel that is twice the width of the aspen's root ball, and just as deep. If you're planting more than one, space the holes at least 15 feet apart.
Set the aspen tree in the hole, making sure the root collar (where the trunk meets the soil) is about 2 inches above the soil line, to allow for settling. Backfill the hole with soil, pressing it firmly against the roots to close air spaces. Drench the root zone with a bucket of water.
Continue watering every other day for the next three weeks, to help roots overcome shock and begin to grow.
Prune branches from the lowest third of the aspen tree to train it upward quickly. Spread a 2- to 4-inch layer of mulch in a 3-foot ring around the aspen, starting 6 inches from the trunk. Mulch will hold moisture in the soil during California's periods of drought.
Cut back new aspen trees that sprout from the original tree's invasive, wide root system annually, unless you want a stand of aspens to develop.