Sorbus ‘Joseph Rock’ Tree

Rocks Mountain Ash trees are an outstanding choice to add colour and interest to a small garden. They also have a special feature – the berries are amber yellow and birds do not realise that they can be eaten, leaving them on the tree as decoration for the entire season!

Sorbus ‘Joseph Rock’ has pinnate foliage which is a light to mid green in summer and matures to a stunning display of red, orange, copper, scarlet and purple in autumn. This truly amazing colour palette will have the children collecting leaves for their autumn school projects and art classes. The tree offers corymbs of creamy white flowers in April and May which turn into the luscious berries as the weather cools down. The contrast between the yellow berries and scarlet leaves create an awe-inspiring focal point in a garden.

Plant your tree in full sun. It is fully hardy and enjoys moist but well-drained sites. It has a tall, neat, upright form and can reach heights of 6m with a spread of 3m in a 20 year period.

As a holder of an RHS Award of Garden Merit, this tree is an excellent choice for a small to medium garden that needs some uplifting, interest and colour. Plant as a stand alone ornamental specimen or plant in a row to create a screen along a wall or to line a driveway.

Sorbus ‘Joseph Rock’ (Mountain ash)

Botanical name

Sorbus ‘Joseph Rock’

Other names

Mountain ash


Sorbus Sorbus

Variety or Cultivar

‘Joseph Rock’ _ ‘Joseph Rock’ is a deciduous tree with dark-green, glossy, pinnate leaves that turn red, yellow and orange in autumn. In spring, it bears flat clusters of creamy-white flowers, followed by yellow, shiny berries in autumn.



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White in Spring

Dark-green in Spring; Dark-green in Summer; Red, Orange, Yellow in Autumn

How to care

Watch out for

Specific pests

Aphids , Blister mite , Sawflies

Specific diseases

Apple and pear canker , Fireblight

General care

Propagation methods

Budding, Grafting, Seed, Softwood cuttings

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Where to grow

Sorbus ‘Joseph Rock’ (Mountain ash) will reach a height of 7.5m and a spread of 7.5m after 10-20 years.

Suggested uses

City, Low Maintenance, Wildlife


Plant in moderately fertile, humus-rich soil. This tree is tolerant of atmospheric pollution.

Soil type

Clay, Loamy, Sandy

Soil drainage

Moist but well-drained, Well-drained

Soil pH

Acid, Neutral


Partial Shade, Full Sun


North, South, East, West


Exposed, Sheltered

UK hardiness Note: We are working to update our ratings. Thanks for your patience.

Hardy (H4)

USDA zones

Zone 7, Zone 6, Zone 5

Defra’s Risk register #1

Plant name

Sorbus ‘Joseph Rock’ (Mountain ash)

Common pest name

grape ground pearl

Scientific pest name

Margarodes vitis



Current status in UK


Likelihood to spread to UK (1 is very low – 5 is very high)

Impact (1 is very low – 5 is very high)

General biosecurity comments

Main pathway; Vitis spp. plants for planting; already prohibited. However; further consideration of other pathways is required.

Defra’s Risk register #2

Sorbus ‘Joseph Rock’ (Mountain ash)

Lance nematode; Nematode; Lance

Hoplolaimus spp.



Nematode species potentially affecting a wide variety of crops; prohibition of soil likely to mitigate risk substantially; keep under review in light of interceptions or findings should they occur in the EU.

Defra’s Risk register #3

Sorbus ‘Joseph Rock’ (Mountain ash)

Cedar-Quince rust; Quince rust; Rust of apple; Rust of juniper; Rust of quince

Gymnosporangium clavipes



EU regulated rust disease which helps mitigate against introduction. A review of EU regulations will help to ensure that all hosts are regulated.

About this section

Our plants are under greater threat than ever before. There is increasing movement of plants and other material traded from an increasing variety of sources. This increases the chances of exotic pests arriving with imported goods and travellers, as well as by natural means. Shoot is working with Defra to help members to do their part in preventing the introduction and spread of invasive risks.

Traveling or importing plants? Please read “Don’t risk it” advice here

Suspected outbreak?

Date updated: 7th March 2019 For more information visit:

( Joseph Rock Sorbus )

(Broad and upright tree with leaves that turn beautiful colors of red, orange, and purple in the fall. Leaves are pinnate and made up of oblong, toothed, bright green leaflets before they turn colors in the fall. Corymbs of white flowers bloom in late spring followed by light yellow berries that turn yellowish orange.

Important Info : It is tolerant of pollution. This cultivar is more prone to fireblight than the species.

Google Plant Images:


Cultivar: Joseph Rock
Family: Rosaceae
Size: Height: 20 ft. to 30 ft.
Width: 15 ft. to 20 ft.
Plant Category: landscape, trees,
Plant Characteristics: decorative berries or fruit,
Foliage Characteristics: coarse leaves, deciduous,
Flower Characteristics: showy,
Flower Color: whites,
Tolerances: pollution,


Bloomtime Range: Late Spring to Early Summer
USDA Hardiness Zone: 7 to 8
AHS Heat Zone: Not defined for this plant
Light Range: Dappled to Full Sun
pH Range: 5 to 7
Soil Range: Sandy Loam to Clay Loam
Water Range: Normal to Moist

Plant Care


How-to : Fertilization for Established Plants
Established plants can benefit from fertilization. Take a visual inventory of your landscape. Trees need to be fertilized every few years. Shrubs and other plants in the landscape can be fertilized yearly. A soil test can determine existing nutrient levels in the soil. If one or more nutrients is low, a specific instead of an all-purpose fertilizer may be required. Fertilizers that are high in N, nitrogen, will promote green leafy growth. Excess nitrogen in the soil can cause excessive vegetative growth on plants at the expense of flower bud development. It is best to avoid fertilizing late in the growing season. Applications made at that time can force lush, vegetative growth that will not have a chance to harden off before the onset of cold weather.


Conditions : Dappled Light
Dappled Light refers to a dappled pattern of light created on the ground, as cast by light passing through high tree branches. This is the middle ground, not considered shady, but not sunny either. Dappled remains constant throughout the day.
Conditions : Types of Pruning
Types of pruning include: pinching, thinning, shearing and rejuvenating.

Pinching is removing the stem tips of a young plant to promote branching. Doing this avoids the need for more severe pruning later on.

Thinning involves removing whole branches back to the trunk. This may be done to open up the interior of a plant to let more light in and to increase air circulation that can cut down on plant disease. The best way to begin thinning is to begin by removing dead or diseased wood.

Shearing is leveling the surface of a shrub using hand or electric shears. This is done to maintain the desired shape of a hedge or topiary.

Rejuvenating is removal of old branches or the overall reduction of the size of a shrub to restore its original form and size. It is recommended that you do not remove more than one third of a plant at a time. Remember to remove branches from the inside of the plant as well as the outside. When rejuvenating plants with canes, such as nandina, cut back canes at various heights so that plant will have a more natural look.
Conditions : Full Sun
Full Sun is defined as exposure to more than 6 hours of continuous, direct sun per day.


Conditions : Moist and Well Drained
Moist and well drained means exactly what it sounds like. Soil is moist without being soggy because the texture of the soil allows excess moisture to drain away. Most plants like about 1 inch of water per week. Amending your soil with compost will help improve texture and water holding or draining capacity. A 3 inch layer of mulch will help to maintain soil moisture and studies have shown that mulched plants grow faster than non-mulched plants.
Conditions : Outdoor Watering
Plants are almost completely made up of water so it is important to supply them with adequate water to maintain good plant health. Not enough water and roots will wither and the plant will wilt and die. Too much water applied too frequently deprives roots of oxygen leading to plant diseases such as root and stem rots. The type of plant, plant age, light level, soil type and container size all will impact when a plant needs to be watered. Follow these tips to ensure successful watering:

* The key to watering is water deeply and less frequently. When watering, water well, i.e. provide enough water to thoroughly saturate the root ball. With in-ground plants, this means thoroughly soaking the soil until water has penetrated to a depth of 6 to 7 inches (1′ being better). With container grown plants, apply enough water to allow water to flow through the drainage holes.

* Try to water plants early in the day or later in the afternoon to conserve water and cut down on plant stress. Do water early enough so that water has had a chance to dry from plant leaves prior to night fall. This is paramount if you have had fungus problems.

* Don’t wait to water until plants wilt. Although some plants will recover from this, all plants will die if they wilt too much (when they reach the permanent wilting point).

* Consider water conservation methods such as drip irrigation, mulching, and xeriscaping. Drip systems which slowly drip moisture directly on the root system can be purchased at your local home and garden center. Mulches can significantly cool the root zone and conserve moisture.

* Consider adding water-saving gels to the root zone which will hold a reserve of water for the plant. These can make a world of difference especially under stressful conditions. Be certain to follow label directions for their use.

Conditions : Normal Watering for Outdoor Plants
Normal watering means that soil should be kept evenly moist and watered regularly, as conditions require. Most plants like 1 inch of water a week during the growing season, but take care not to over water. The first two years after a plant is installed, regular watering is important for establishment. The first year is critical. It is better to water once a week and water deeply, than to water frequently for a few minutes.


How-to : Pruning Trees After Planting
It is critical to prune trees correctly from the beginning to assure proper growth and development. Young trees can be transplanted in a number of forms: bare root, balled & burlap and in containers. The more stress the plant undergoes in the transplant process, the more pruning that is required to compensate.

Deciduous trees like maples (those that loose their leaves in the fall) can be dug up and sold with their bare roots exposed. Because most of the root system is lost in digging, sufficient top growth should be removed to compensate for this loss. This may be done at the nursery before you buy the plant or you may have to prune at the time of planting. Select and head back the best scaffold branches, i.e. those branches which will form the main lateral structure of the future mature tree. Remove all other extraneous side branches. If the tree seedling does not have branches, allow it to grow to the desired height of branching then pinch it back to stimulate the lower buds to form branches.

Ball and burlap trees are dug up with their root systems somewhat intact. This was mostly done for conifers and broadleaf evergreens, but has become common for deciduous trees as well. Since some root mass is lost in the digging stage, a light pruning is generally called for. Head back the plant to compensate for this loss and to promote branching.

Trees that are grown in containers generally do not loose roots in the transplanting phase. Therefore you do not generally have to prune them unless there is some root injury or limb damage in the planting process.

Once you have your trees planted, be patient. Do not remove shoots from the trunk early on as these allow the tree to grow more rapidly and also shade the tender young trunk from sun-scald. Wait a few years to begin training the tree to its ultimate form.
How-to : Planting Shrubs
Dig a hole twice the size of the root ball and deep enough to plant at the same level the shrub was in the container. If soil is poor, dig hole even wider and fill with a mixture half original soil and half compost or soil amendment.

Carefully remove shrub from container and gently separate roots. Position in center of hole, best side facing forward. Fill in with original soil or an amended mixture if needed as described above. For larger shrubs, build a water well. Finish by mulching and watering well.

If the plant is balled-and-burlapped, remove fasteners and fold back the top of natural burlap, tucking it down into hole, after you’ve positioned shrub. Make sure that all burlap is buried so that it won’t wick water away from rootball during hot, dry periods. If synthetic burlap, remove if possible. If not possible, cut away or make slits to allow for roots to develop into the new soil. For larger shrubs, build a water well. Finish by mulching and watering well.

If shrub is bare-root, look for a discoloration somewhere near the base; this mark is likely where the soil line was. If soil is too sandy or too clayey, add organic matter. This will help with both drainage and water holding capacity. Fill soil, firming just enough to support shrub. Finish by mulching and watering well.
How-to : Planting a Tree
Dig out an area for the tree that is about 3 or 4 times the diameter of the container or rootball and the same depth as the container or rootball. Use a pitchfork or shovel to scarify the sides of the hole.

If container-grown, lay the tree on its side and remove the container. Loosen the roots around the edges without breaking up the root ball too much. Position tree in center of hole so that the best side faces forward. You are ready to begin filling in with soil.

If planting a balled and burlaped tree, position it in hole so that the best side faces forward. Untie or remove nails from burlap at top of ball and pull burlap back, so it does not stick out of hole when soil is replaced. Synthetic burlap should be removed as it will not decompose like natural burlap. Larger trees often come in wire baskets. Plant as you would a b&b plant, but cut as much of the wire away as possible without actually removing the basket. Chances are, you would do more damage to the rootball by removing the basket. Simply cut away wires to leave several large openings for roots.

Fill both holes with soil the same way. Never amend with less than half original soil. Recent studies show that if your soil is loose enough, you are better off adding little or no soil amendments.

Create a water ring around the outer edge of the hole. Not only will this conseve water, but will direct moisture to perimeter roots, encouraging outer growth. Once tree is established, water ring may be leveled. Studies show that mulched trees grow faster than those unmulched, so add a 3″” layer of pinestraw, compost, or pulverized bark over backfilled area. Remove any damaged limbs.


Pest : Sawfly Larvae
Sawflies look similar to wasps, but do not have stingers or waists. Sawflies were named for the way the females “”sawed”” openings into hosts, where eggs were laid. The larvae of the sawfly is the actual villain, causing damage to fruit or foliage as it matures. The small, green larvae of the sawflies are caterpillar-like or slug-like in appearance.

Prevention and Control: No prevention available. Control by handpicking or spraying with a recommended insecticide. Birds, beetles and viruses usually keep the sawfly under control.

Pest : Aphids
Aphids are small, soft-bodied, slow-moving insects that suck fluids from plants. Aphids come in many colors, ranging from green to brown to black, and they may have wings. They attack a wide range of plant species causing stunting, deformed leaves and buds. They can transmit harmful plant viruses with their piercing/sucking mouthparts. Aphids, generally, are merely a nuisance, since it takes many of them to cause serious plant damage. However aphids do produce a sweet substance called honeydew (coveted by ants) which can lead to an unattractive black surface growth called sooty mold.

Aphids can increase quickly in numbers and each female can produce up to 250 live nymphs in the course of a month without mating. Aphids often appear when the environment changes – spring & fall. They’re often massed at the tips of branches feeding on succulent tissue. Aphids are attracted to the color yellow and will often hitchhike on yellow clothing.

Prevention and Control: Keep weeds to an absolute minimum, especially around desirable plants. On edibles, wash off infected area of plant. Lady bugs and lacewings will feed on aphids in the garden. There are various products – organic and inorganic – that can be used to control aphids. Seek the recommendation of a professional and follow all label procedures to a tee.
Fungi : Powdery Mildew
Powdery Mildew is usually found on plants that do not have enough air circulation or adequate light. Problems are worse where nights are cool and days are warm and humid. The powdery white or gray fungus is usually found on the upper surface of leaves or fruit. Leaves will often turn yellow or brown, curl up, and drop off. New foliage emerges crinkled and distorted. Fruit will be dwarfed and often drops early.

Prevention and Control: Plant resistant varieties and space plants properly so they receive adequate light and air circulation. Always water from below, keeping water off the foliage. This is paramount for roses. Go easy on the nitrogen fertilizer. Apply fungicides according to label directions before problem becomes severe and follow directions exactly, not missing any required treatments. Sanitation is a must – clean up and remove all leaves, flowers, or debris in the fall and destroy.
Diseases : Anthracnose
Anthracnose is the result of a plant infection, caused by a fungus, and may cause severe defoliation, especially in trees, but rarely results in death. Sunken patches on stems, fruit, leaves, or twigs, appear grayish brown, may appear watery, and have pinkish-tan spore masses that appear slime-like. On vegetables, spots may enlarge as fruit matures.

Prevention and Control: Try not to over water. If your climate is naturally rainy, grow resistant varieties. In the vegetable garden, stake and trellis plants to provide good air circulation so that plants may dry. Increase sunlight to plants by trimming limbs. Prune, remove, or destroy infected plants and remove all leaf debris. Select a fungicide that is labeled for anthracnose and the plant you are treating. Follow the label strictly.
Pest : Scale Insects
Scales are insects, related to mealy bugs, that can be a problem on a wide variety of plants – indoor and outdoor. Young scales crawl until they find a good feeding site. The adult females then lose their legs and remain on a spot protected by its hard shell layer. They appear as bumps, often on the lower sides of leaves. They have piercing mouth parts that suck the sap out of plant tissue. Scales can weaken a plant leading to yellow foliage and leaf drop. They also produce a sweet substance called honeydew (coveted by ants) which can lead to an unattractive black surface fungal growth called sooty mold.

Prevention and Control: Once established they are hard to control. Isolate infested plants away from those that are not infested. Consult your local garden center professional or Cooperative Extension office in your county for a legal recommendation regarding their control. Encourage natural enemies such as parasitic wasps in the garden.
Diseases : Blight
Blights are cause by fungi or bacteria that kill plant tissue. Symptoms often show up as the rapid spotting or wilting of foliage. There are many different blights, specific to various plants, each requiring a varied method of control.


Conditions : Fall Color
Fall color is the result of trees or shrubs changing colors according to complex chemical formulas present in their leaves. Depending on how much iron, magnesium, phosphorus, or sodium is in the plant, and the acidity of the chemicals in the leaves, leaves might turn amber, gold, red, orange or just fade from green to brown. Scarlet oaks, red maples and sumacs, for instance, have a slightly acidic sap, which causes the leaves to turn bright red. The leaves of some varieties of ash, growing in areas where limestone is present, will turn a regal purplish-blue.

Although many people believe that cooler temperatures are responsible for the color change, the weather has nothing to do with it at all. As the days grow shorter and the nights longer, a chemical clock inside the trees starts up, releasing a hormone which restricts the flow of sap to each leaf. As fall progresses, the sap flow slows and chlorophyll, the chemical that gives the leaves their green color in the spring and summer, disappears. The residual sap becomes more concentrated as it dries, creating the colors of fall.
Glossary : Deciduous
Deciduous refers to those plants that lose their leaves or needles at the end of the growing season.

Sorbus ‘Joseph Rock’

Sorbus tree in a pot and probelm on my Lemon tree Hello Crocus, I used to have a wonderful Sorbus ‘Joseph’s Rock’ in my previous small garden. I now have an even smaller garden set to raised beds contained by sleepers on 3 sides and paved in the centre with many pots. I would like to grow another ‘Joseph’s Rock’, but this time it would have to be in a tub. Is this feasible? If so how big should the pot be initially? Would it have to be upped in size every couple of years, or can it be put in a large one straight away and left to grow into it and what about feeding it? A second problem I have is with a lemon tree, grown in a conservatory. This is its second year and it has produced 6 lemons – 5 still on the tree. I repotted it in citrus compost in a 9″ pot and I have fed it weekly with the citrus feed I bought from you. For the past 3-4 weeks it has been exuding a stickiness which I think comes from a scale-like condition I have noticed mainly nestling along the ribs of the underside of the leaves, but also on some branches where the leaves join. A few leaves have started to go brown and curl at the tips. I have spent a lot of time trying to clean off the scale and did give it a spray a few days ago with a natural liquid containing neep oil. Still the stickiness is there every morning. What else can I do?! Yours hopefully, Pamela P.S. Do I need to continue Summer feeding while the lemons are still growing, or do I need to switch to the Winter feed regardless? The lemons grow very slowly!

Pamela Hodges


Hello Pamela, It is possible to grow this tree in a really large pot, but after several years it will start to struggle. You can either pot it up every couple of years, but I would buy the largest pot you can find and plant it straight out using John Innes No3 compost. As for the lemon, you should change to winter feed soon, and keep on removing the scale by hand. If you get rid of all of them then the stickiness will stop, but you should avoid using any chemicals on an edible crop. I hope this helps. Helen Plant Doctor


Crocus Helpdesk

Sorbus tree as focal point for our new development Hi, I was just looking at your website, and was wondering if your Sorbus ‘Joseph Rock’ – Mountain Ash would be suitable in a shaded areas against an adjoining flank wall to our neighbour. Or would you have any other ideas? It is for an inner city location, and requires fairly low maintenance. The vicinity of next door’s wall may hinder it’s lateral growth. Would be nice to see something a little unusual as a focal point in a very small communal space. Await your response! Thanks Ian

Ian Brown


Hello Ian, These trees prefer a sunnier spot, and I would never recommend planting a tree very close to a structure. A better alternative would be either a Pyracantha or a Cotoneaster, both of which can be trained to grow flat on a trellis or network of wires on the wall. I hope this helps. Helen Plant Doctor


Ian Brown

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