Fraxinus

Graceful, unfussy and low-maintenance, ash trees suit a broad range of sites

F. excelsior 'Jaspidea'. Image: Garden Picture Library
F. excelsior 'Jaspidea'. Image: Garden Picture Library

Ash trees make great specimens for large gardens and are useful shade trees for streets and parks. However, they are seen by many customers as a weedy type of tree because ash saplings can be seen thriving on uncultivated areas and roadsides everywhere, like sycamore.

Part of the reason ash seedlings do well is because the genus as a whole thrive in almost any soil and tolerate windswept and coastal localities and polluted areas. Many ashes also provide fabulous autumn colour and several have attractive blossom.

Fraxinus is an extensive genus of about 65 species of mainly hardy, fast-growing trees with pinnate leaves, within the olive family, Oleaceae. All of the trees are deciduous, apart from the evergreen F. uhdei.

The most well-known ashes, such as the white ash (F. americana) and the British native common ash (F. excelsior), are large trees both capable of reaching 40m in height. But the genus also includes smaller trees and shrubs such as F. ornus Award of Garden Merit (AGM), which bears long panicles of fragrant, creamy white flowers in the spring and whose foliage turns yellow, red and orange in the autumn.

There are varieties that stand out for their autumn colour alone, including F. americana 'Autumn Purple', F. angustifolia 'Raywood' AGM and F. ornus 'Louisa Lady'. There is even a variety of the British native known as the golden ash, F. excelsior 'Jaspidea' AGM, whose contrasting yellow stems and black buds provide winter interest.

Ash trees are generally tolerant of various different soil types, even heavy and alkaline conditions. However, there are wet soil species, including F. nigra, F. tomentosa and F. caroliniana. Conversely F. cuspidata, F. ornus AGM and F. angustifolia are adapted to drier soils.

Fraxinus should be planted while dormant in any deep, moist loam. They are gross feeders and develop extensive fibrous root systems, which makes transplanting easy. Throughout the formative years, a vigorous leader should be allowed to develop. Weak, forked crotches may cause structural problems when the plant is mature.

Stratified seed can be sown in spring or cultivars grafted in spring or budded in summer onto seedling stock of the same species under glass.

Fraxinus is susceptible to ash heart rot (Inonotus hispidus), ash bark beetle (Hylesinus fraxini), Armillaria root rot, bacterial canker (Pseudomonas savastanoi), canker (Nectria galligena), powdery mildew (Phyllactinia corylea), Arabic mosaic virus and the fungus Daldinia concentrica.

 

WHAT THE SPECIALISTS SAY

Simon Hunt, manager, Landford Trees, Wiltshire "We don't sell many of the common ash, but a lot of F. pennsylvanica and F. angustifolia 'Raywood' AGM, which is one of my personal favourites. Both have great autumn colour. Also, they don't set seed in this country, so you don't get seedlings coming up everywhere.

"The manna ash, F. ornus AGM, is very popular as well. Unlike most other ashes, it has significant flowers, and forms a small, bushy tree. Ashes in general are pretty disease-free and are standing up to climate change well. They are easy trees to grow, coping with most types of soil."

Kevin Marsh, grower, Beeches Nursery, Saffron Walden, Essex "There are some nice varieties such as F. ornus AGM, which has frothy white flowers in the summer. F. americana 'Autumn Purple', as its name suggests, has good autumn colour. F. excelsior 'Jaspidea' AGM can be planted for its foliage and the stem colour of young trees - in winter the black buds on yellow stems really stand out.

"But I think one of the problems with ash is that customers see them as a bit of a menace, with seedlings that pop up everywhere. I haven't sold one this year - nobody wants them. I think it's mainly because many people have small modern gardens now. They are large trees so only really fit in large gardens. But on the plus side, they are easy trees to propagate and are not affected by any major pests."

 

IN PRACTICE

Mark Gregory, managing director, Landform Consultants, Surrey "I like ash for several reasons. They are big so they are effective in large areas and in streetscapes. A single species in a car park, say, can look striking. There are also some great cultivars for autumn colour - the golden ash F. excelsior 'Jaspidea' AGM and F. angustifolia 'Raywood' AGM, which are superb trees. They provide very rich colour but I bet people driving along the road and noticing them won't realise they are ash trees.

"Ash trees really behave themselves - they don't need copious amounts of water, their tops don't blow out, few pests affect them and they don't produce huge amounts of leaf litter. For a big tree you also get a lot for your money. They are affordable, and in this time when budgets are getting slashed the low cost of the tree as well as maintenance and pruning costs mean that ash should be considered for landscape projects.

"Another good thing is that it is a fantastic burning wood. It can be burnt green and I use common ash in my wood-burning stove. The downside of ash is that they are not good for winter screening, as their branch structure is so open."

 

SPECIES AND CULTIVARS

- F. americana or the white ash is a large, fast-growing tree that can reach 40m. It has brown winter buds.

- F. americana 'Autumn Purple' is a fast-growing conical tree with dark green leaves that turn reddish purple in autumn. Considered by some to be superior to F. angustifolia 'Raywood'.

- F. angustifolia 'Raywood' Award of Garden Merit (AGM) is a fast-growing ash of medium height (10-15m when mature) with a dense, upright, oval and relatively compact habit. Its dark green leaves turn wine red in the autumn.

- F. excelsior is the common ash, easily recognised when dormant by its black, velvety buds. Probably our toughest native tree, it thrives on most soils, including calcareous, and will tolerate windswept, exposed sites, coastal locations and air pollution. Up to 40m.

- F. excelsior 'Althena' is a medium to large tree of pyramidal habit. It tends to retain its central leader longer than common ash, giving it more structural strength. Up to 15-20m, it is recommended for avenues and street planting.

- F. excelsior f. diversifolia is unique among ashes. This form has simple or sometimes three-parted leaves, earning its common name, the one-leaved ash. A fast-growing tree with pyramidal form that reaches more than 20m.

- F. excelsior 'Jaspidea' AGM - the golden ash has yellow twigs that are an effective winter feature when the tree is small. It should not be confused with 'Aurea'; 'Jaspidea' is much more vigorous. Up to 15-20m.

- F. excelsior 'Pendula' AGM is the weeping ash. It makes a fine specimen tree in a park or large garden. Up to 10-15m.

- F. excelsior 'Westhof's Glorie' AGM is often selected over the common ash for its more uniform shape. It is a fast-growing cultivar that has a narrow habit when young, spreading to become broadly oval as it matures. Grows to more than 20m.

- F. ornus AGM, the flowering or manna ash, is slow-growing and matures to a rounded shape. Creamy white, fragrant blossoms are produced in spring. The foliage also turns yellow, red and orange in autumn. Grows to 8m.

- F. ornus 'Arie Peters' is one of the loveliest flowering ash cultivars, with 10-15cm long panicles of flowers throughout the crown in the growing season.

- F. ornus 'Mecsek' is a lollipop form suitable for streets and avenues where space is limited. At most it grows to 7m high, is slow-growing and has shiny, dark green leaves.

- F. ornus 'Louisa Lady' has spectacular autumn colour, richer than that of the species, and stronger in structure than F. angustifolia 'Raywood' AGM.

- F. ornus 'Obelisk' has a narrow, columnar habit, making it suitable for restricted urban areas and smaller gardens. It stands up well to paving and soil compaction.

- F. pennsylvanica is a fast-growing tree that can grow to 18m tall. An irregularly-shaped tree when young, it becomes oval shaped with age. It bears glossy dark green foliage, which turns yellow in autumn.

- F. pennsylvanica 'Summit' is a fast-growing, medium to large tree, with ascending branches that form a broadly conical, uniform crown, making it suitable for avenue plantings.


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