Root cuttings
Aspen doesn’t often produce seed and, if it does, it’s very light and fluffy, which makes it extremely difficult to collect. So a different method is needed entirely!
In the same family as willows, aspen grows readily from cuttings. To get good material for these cuttings, root cuttings are first taken.
In late winter or early spring, expose roots on mature trees and remove sections that are 1-3cm in diameter. Cut these into 30cm sections and store in bags, wrapped in moist paper or compost. Don’t let the roots dry out.
Do not return to the same trees year after year as continual taking of root cuttings will weaken the mature trees.
Producing suckers
Plant the prepared root cuttings as soon as you can after collection. The roots are placed in suitable containers a few centimetres apart and covered with compost. Place the containers somewhere unheated, but protected from the elements. A polytunnel is ideal. Keep moist, but not wet.
After a few weeks, bright green suckers will begin to emerge from the compost.
Rooting the suckers
When the suckers are 5-7cm tall, cut them off the roots with a sharp knife. Scissors or secateurs will crush the stem, so it’s important to use the sharpest, cleanest knife you have.
Trim the cutting below a leaf node if necessary, dip in rooting hormone, and plant like you would any cuttings – into a gritty compost made up of 50% sharp sand or grit and 50% compost.
These cuttings should be placed in a warm place and kept moist at all times. If you’ve planted your cuttings into pots (5 or 6 to a pot), you could cover the pot with a clear polythene bag and secure it with an elastic band. This will recycle the moisture that evaporates from the compost, allowing it to condense on the plastic and run back into the compost. It also maintains a still, humid atmosphere.
The cuttings should produce roots in about 4 weeks.
Growing
Once rooted, the plastic bag can be removed and the plants acclimatised to outdoor conditions – a cold frame is best for this.
After a few more weeks, the individual plants can be potted into their own pots and grown on. Provided they receive enough moisture and are fed regularly (you can use a liquid or granular feed every 4-6 weeks until the middle of July), aspen cuttings will grow quite fast and be ready to plant out in the autumn.
Planting
Prepare the site well by clearing away any weeds or grass and make a hole big enough to accommodate the root ball. Place the roots carefully in the hole (removing the pot if they had one). Make sure the stem is at the same depth as it was in the pot/ground, and firm back the soil.