How to Grow and Care for European Mountain Ash

European mountain ash, also commonly known as the rowan tree, is a deciduous tree with white flowers but it is grown mostly for its distinctive clusters of red berries that mature in the late summer and persist to add vivid color to a winter landscape. European mountain ash grows best in cool mountainous conditions, and requires full to partial sun, acidic, moist soil, and thrives in unpolluted, salt-free areas.

European Mountain Ash Care

Here are the main care requirements for growing European mountain ash:

• Place the tree in full but not scorching hot sun.
• Plant European mountain ash in acidic soil.
• Prune only at the end of winter.

Light

This tree requires full sun at least six to eight hours per day. Some partial sun is better than scorching sun, which can make the tree decline.

Soil

Perform a soil test to ensure the soil is acidic, in the range of 4.5 to 6.0, which this tree prefers. You can add amendments to acidify the soil if the soil pH is too high. This tree does best in moist, well-drained soils. It will not thrive in compact or salty soils.

Water

The tree needs a medium amount of water to keep the soil moist. However, it may not need any supplemental water if there is normal rain. If there is not an average rainfall, it can be given 1 inch of water every week.

Temperature and Humidity

It will not grow well south of USDA Zones 5 and 6. As the common name suggests, this tree prefers cool mountain climates and dislikes hot and humid summers.

Fertilizer

This tree does not need any fertilizer if the soil is rich, moist, or it's amended with compost. The tree may benefit from a feeding if the soil is extremely poor, which would mean it's dry, crumbling, cracked, and compact without moisture or nutrients.

Types of European Mountain Ash

• ‘Fructo Luteo’: Grows to 25 feet tall (half the size of a typical rowan) and produces golden yellow fruits.
• ‘Sheerwater Seedling’: Grows very narrow than typical European mountain ash with fiery reddish-orange autumn foliage color and is frequently used for street plantings.

Pruning

Fire blight can be spread by pruning if the conditions are right (very warm). Prune this tree at winter's end during the tree's dormant period.

Propagating European Mountain Ash

Propagate this tree with semi-hardwood cuttings. Cuttings will only work with this tree if it's young. A cutting from an older European mountain ash tree may not reproduce well. If you have a newer tree and would like to grab a cutting, do so in the spring when there's new growth so you directly plant the cutting. Here's how:

1. Find a branch with new growth but one that is somewhat woody, but that is not old or brown.
2. With a sterile cutting tool, cut a 6 to 8-inch long piece right below a node. Remove all the leaves on the cutting but leave the pair on top of the stem. (Cut large leaves in half if they are in the way.)
3. Create a couple of vertical wounds on the bottom of the cutting, about 1 inch long. Dip the wounded end in rooting hormone.
4. Place the cutting directly into the prepared ground of peat moss, sand, perlite, and water.
5. Keep the ground moist (not soggy) and roots should take hold in four to six weeks if there is enough sun to keep it warm.

How to Grow European Mountain Ash From Seed

It's very easy to propagate a European mountain ash tree from the seeds of the fruit. The seeds will need to go through the stratification process. Here's how to grow this tree from seed:

1. Harvest the berries in August or early September to extract the seeds.
2. Stratify the seeds by putting them in a plastic bag and into a freezer for 90 days. Thaw them to room temperature and put into your refrigerator for 60 days.
3. Plant seeds in a small pot no more than 1 inch deep in potting soil.
4. Keep soil evenly moist, but not soggy.
5. If necessary, repot into larger containers with a peat moss, compost, and sand mixture until the seedlings are ready to be placed in their permanent outdoor spot in the spring.

Common Pests and Plant Diseases

European mountain ash trees can attract several pests that can cause problems, including:

• Aphids: This pest sucks sap from young leaves and weakens the plant, but they can be knocked off with a blast of water or insecticidal soap.
• Apple fruit moth (Argyresthia conjugella): Larvae bores into the berries but good air circulation can help the problem.
• Blister mites: Pests produce small galls or blisters on foliage and fruit, often attacking a neglected tree.
• Mountain-ash sawfly larvae (Pristiphora geniculata): Devours foliage and can defoliate the tree but specific pesticides control the problem.
• Oystershell scale (Lepidosaphes ulmi): This pest attacks stressed trees and cause branch dieback. Insecticides or organic options like horticultural oil or insecticidal soap will help.

In addition to pests, this tree can be afflicted with various bacterial and fungal diseases, including:

• Apple scab (Venturia inaequalis): This fungal disease occurs in high humidity and rainfall, affecting foliage and fruit with olive-green blotches.
• Botryosphaeria (Botryosphaeria dothidea): Fungal problem that causes canker and branch dieback. Cultural control, disposal of dead material, and fungicides help.
• Cedar-quince rust (Gymnosporangium clavipes): This fungal problem attacks plants in the rose family, causing flaky branch coverings and infected fruits. Remove infected portions of the tree and apply fungicides at the correct time.
• Cytospora canker (Cytospora spp.): Though this airborne fungal disease is more prevalent in spruce trees, it can also get into wounds of the European mountain ash tree and cause cankers and branch dieback in the canopy. There is no cure except to manage the disease by pruning out dead parts of the tree.
• Bacterial fire blight: (caused by Erwinia amylovora): This condition happens when the tree is growing in conditions that are too hot for the plant. Prune affected branches right away.
• Honey fungus: Shows as white growth between bark and wood at the ground, sometimes honey-colored mushrooms accompany the problem. There is no control or prevention for this deadly disease that spreads underground.
• Powdery mildew: This common fungal issue that deposits dusty particles on foliage occurs in high humidity and is treated with fungicides.
  

Common Problems With European Mountain Ash

This tree can be very tough and enduring in spite of all the pests and diseases that may be problematic if it's not planted in the cool conditions it prefers. You'll also find deer grazing on the tree's leaves. But it's best to be on the lookout for some signs that can indicate the tree may need some help.

Brown/Black Leaves

The tree may have leaf spot, which shows up as brown spots on leaves that develop black spores and leaf drop. Fire blight shows as black leaves and browning flower clusters.

Splitting Bark

Usually sloughing or splitting bark is a normal regenerative process for trees. Excessive splitting may be the result of too many crossed branches stressing the bark. However, for a European mountain ash, it's best to peel away some of the bark and take a whiff. If there is a mushroom-like smell, the tree may be afflicted with a "honey" fungus.

No Flowers or Berries

The tree could be waterlogged or sitting in very compact or salty soil.

Blue Growth on Branches

This is likely lichen (composite fungal and algae-like organisms that grow on trees to form a symbiotic relationship), which tends to needlessly worry tree owners. But this is only a surface issue and indicates that the air around the tree is healthy.