Mountain ash, or Sorbus Americana, is a species of small, fruit-bearing tree native to the northeastern United States and eastern Canada. It is easily recognisable by its dull green, pinnate leaves, which become brilliant salmon-pink in autumn. In late summer, it bears a crop of orange berries in dense clusters on the tips of the branches. The berries contain small black seeds that propagate easily when planted in moist, draining soil. While propagating mountain ash trees from seed is easy, the seedlings have a high rate of mortality due to dampening off.
Gather berries from a healthy mountain ash tree in September when they are fully ripe and beginning to wrinkle. Gather and sow the berries within 24 hours for the best results.
Mix two parts potting soil, two parts horticultural sand, two parts peat moss, one part composted manure and one part leaf mould to create an acidic seed-starting mix suited to growing mountain ash seeds. Test the soil's acidity with a pH test kit to ensure that the soil has a pH of between 4.7 and 6.0.
Fill several 2-gallon plastic nursery pots with the mixture.
Apply 7 inches of water to each pot with a garden hose with an adjustable nozzle set to shower or mist. Allow the moisture to drain away for an hour before sowing the seeds in the mixture. Place the pots in a sunny location to warm the soil.
Poke a 1/2-inch-deep hole in each pot of soil. Place two berries in each hole, bury them and water them to a depth of 3 inches.
Place the pots where they will receive at least four hours of direct sunlight per day and temperatures within five degrees of 18.3 degrees Celsius during the day. Move the pots into a greenhouse for 30 days in areas with a short growing season.
Move the pots outdoors so they will be exposed to the cold over the winter since mountain ash seeds require exposure to temperatures below 40 degree Fahrenheit for at least 60 days to germinate.
Apply 4 inches of water every 10 days if the weather conditions are very dry. Do not water the seeds if they are receiving regular precipitation, whether in the form of rain or snow, since mountain ash seedlings are susceptible to dampening off.
Move the pots to a sunny spot in early spring.
Stretch cling film across the top of the pot to help warm the soil and prompt germination. Remove the cling film after 30 days, or when outdoor air temperatures stay above 15.6 degrees Celsius during the day.
Remove the weaker of the two seedlings from each pot when they reach 4 inches in height. Apply 1 teaspoon of 0-10-10 ratio fertiliser diluted in 1/2 gallon of water around the base of each seedling.
Plant the saplings in a permanent location when they reach 10 inches in height and have several pairs of mature leaves. Choose a sunny, well-draining site to plant them in and water them to a depth of 7 inches every 10 days during the growing season.
Do not attempt to remove the individual seeds from the mountain ash berries because they emit a toxic substance when exposed to water.