Cercis

Blooming on bare stems, this plant looks striking as a specimen or grouped, says Miranda Kimberley.

Cercis canadensis - image: Floramedia
Cercis canadensis - image: Floramedia

Small trees are much coveted by homeowners with small gardens and Cercis is a dainty example of a diminutive tree or large shrub that adds a lot of value. It has distinctive, heart-shaped foliage and produces beautiful pea flowers in the spring. The flowers often bloom directly from the trunk and branches, adding an extra interesting feature.

Cercis copes well being pruned hard once the flowering is over in late spring, so they can be kept to a reasonable size if necessary. The most commonly-grown species - the Judas tree, Cercis siliquastrum Award of Garden Merit (AGM) - hails from the eastern Mediterranean region. It therefore tolerates dry soils and a sunny aspect so it is highly suitable for planting in urban gardens as well as courtyards.

The pea flowers give away the fact that Cercis is placed in the legume family. There are six or seven species - all deciduous trees and shrubs - and these are distributed throughout temperate northern regions, including China, the Mediterranean and North America.

C. siliquastrum is the best known, but there is also C. Canadensis - the North American redbud - which is the largest tree, reaching 14m tall. It has variable hardiness depending on the provenance, but trees grown from northern sources can survive down to -30 degsC. There are many popular cultivars bred from this species, including the purple-leaved C. 'Forest Pansy' (AGM).

C. siliquastrum is hardy down to around -15 degsC. Frosts can sometimes knock it back, but then it may sprout from the base.

Two other North American species, C. occidentalis and C. reniformis, are similar in habit. They are more shrubby, although can become small trees of 5m or 12m respectively. Along with C. chinensis, which is a large, densely-branching shrub of upright habit, they are the least hardy of the genus and will not do well in colder parts of the UK. Plant them in sheltered parts of a woodland or in the garden, perhaps against a wall.

The taller species make lovely specimen trees in parks or gardens and the shrubby types are effective in group plantings. The varieties with colourful leaves can be treated as shrubs in the border and maintained by hard pruning, which leads to a more showy display.

Cercis are adaptable to a wide range of soils, but ideally they should be planted in well-drained but moisture-retentive loamy soils. They do not do well in wet soils, especially those with a heavy clay subsoil. Conversely, there are many examples of Cercis thriving where the subsoil is chalk. They love the sun but still like their roots to be moist - C. canadensis actually occurs naturally in moist woodland. Plant them out of the way of cold, drying winds.

They must be transplanted at an early age because they resent disturbance. Young growth is sometimes prone to frost damage, but cut out dead and diseased wood quickly and they should regenerate. Specimens can be left to develop naturally and pruning is not necessary other than removing dead wood. But if larger foliage or a smaller habit is wanted, they can be cut back quite hard. This is best done in mid to late spring after flowering. Do watch out for coral spot fungus because this is something to which Cercis are susceptible.

What the specialists say

- Robert Vernon, co-owner, Bluebell Nursery & Arboretum, Derbyshire

"My favourite is the unusual C. canadensis 'Royal White'. It is a rare and free-flowering cultivar that produces flurries of pure-white, pea-like flowers. They emerge on the bare stems before the leaves in spring. The mass of white flowers almost makes it look like a dusting of snow has settled on the branches.

"The heart-shaped leaves are bronze-green when they emerge, turning dark green later in the summer and handsome shades of yellow before falling in autumn. It is an exquisite garden plant.

"There are two other important things to know about Cercis. They do not transplant well and should be left undisturbed once planted in position. Please do not feed Cercis with artificial plant food after planting it out because this can severely damage the root system. They need as much sun as possible and watering until settled down."

- Stephanie Dunn James, assistant managing director, FP Matthews, Worcestershire

"There are several new, exciting varieties to add to the still reliable C. canadensis 'Forest Pansy' (AGM)and 'Avondale'. These would include C. canadensis 'Hearts of Gold' (which has bright-gold leaves with lavender flowers, even on young plants), C. canadensis Lavender Twist (contorted branches with pinky/purple flowers) and the very recent C. texana 'Merlot' (a darker leaf than C. 'Forest Pansy') and C. 'Ruby Falls' (a weeping red-leaved form). There are several exceptional floriferous forms such a C. chinensis 'Shirobana' (white) and C. reniformis 'Oklahoma' (rose/magenta). We are spoilt for choice.

"Because of their exotic look, Cercis have a reputation for being tender, but in fact most are very hardy and suit most well-drained soil types. With spring flower (white and pink) and soft summer foliage (red and yellow), they make good large shrubs or small trees.

"To enhance the size of the magnificent heart-shaped leaves and contain their size, they will take relatively heavy pruning. It is best carried out in mid to late spring after flowering. They should be given some shelter from prevailing winds."

In practice

- Tony Kirkham, head of the arboretum and horticultural services, Royal Botanic Gardens, Kew

"I love C. siliquastrum AGM. It is an incredible tree, with its flowers blooming directly from the trunk, and full of character, especially the veteran trees you find in historic gardens. The best ones I have seen are at Guildford Castle.

"As the bark ages, it becomes covered with burrs and knots, which makes me think of other characterful trees such as Parrotia and Morus nigra.

"We have struggled to grow the North American species C. canadensis at Kew. Of course, C. 'Forest Pansy' is incredibly popular because of its dark-purple leaves, but for whatever reason it has not done well and specimens have just stayed in the nursery beds because they are not strong enough to plant out."

Species and varieties

- C. canadensis or the North American redbud is a species from the eastern USA. It is similar in size to the more common C. siliquastrum AGM (H4) but has thinner leaves. It produces pale-rose flowers on bare stems in the spring, before young bronze leaves emerge. They turn yellow in autumn. Fully hardy, down to -15 degsC, but possibly more tender when young. Height and spread: 10m.

- C. canadensis 'Cascading Hearts' is a small, rounded tree with a weeping habit. It produces purple-mauve flowers between April and May. Height: 3-4m.

- C. canadensis 'Forest Pansy' AGM (H4) has deep reddish-purple foliage. It needs a sunny, south-facing position to develop the best colour. The pea-like flowers emerge in spring before the leaves and can be red, pink or white. Height and spread: 10m.

- C. canadensis 'Hearts of Gold' is a striking new variety with clear golden-yellow, heart-shaped leaves in spring that darken to pale green later in the year. Its pale purple-pink flowers bloom on bare stems in spring before the leaves emerge. Forms a large shrub or very small tree. Height and spread: 6m.

- C. canadensis Lavender Twist = 'Covey' is a small weeping tree. It has black branches against which the vivid pink flowers stand out. The heart-shaped leaves are bronze when young, turn blue-green and then yellow in autumn. Height: 3m.

- C. canadensis var. texensis 'Texas White' produces white flowers and has a spreading habit, and is often grown multi-stemmed, becoming a tall shrub or small tree. Height and spread: 10m.

- C. chinensis 'Avondale' is a popular variety bred from the Chinese species. Purple-pink flowers are produced on bare stems in late April or early May before the broad, heart-shaped foliage emerges. Likes full sun or light shade. Height: 8m. Spread: 6m.

- C. chinensis 'Don Egolf' is an unusual and compact new selection suitable for smaller gardens. It produces rosy-mauve flowers in early spring. Best in full sun. Height: 5m. Spread: 4m.

- C. occidentalis is a species from the south western USA. It becomes a large shrub or very small tree. Its flowers are bright-pink or magenta coloured and emerge on bare branches in spring. The leaves are heart-shaped and dark green. Height 4m and spread: 3m.

- C. siliquastrum AGM (H4) is the Judas tree, hailing from the eastern Mediterranean and the most commonly grown Cercis in the UK. It is a slow grower, with staking recommended in the first few years, but will become a well-rounded small tree. The heart-shaped leaves are bronze when young, turn blue-green and then yellow in autumn. The small pink flowers appear on bare stems before and with the leaves. Long, flat pods follow in autumn. It is fully hardy down to -15 degsC, although more tender when young. Height and spread: 10m.

- C. siliquastrum 'Bodnant' is a small tree that produces masses of vivid dark purple/pink flowers in May before the leaves emerge. The foliage is heart-shaped, bronze to burgundy when young, darkening to green in summer before turning yellow in autumn. Likes full sun or partial shade. Height: 10m. Spread: 8m.

Thank you to Floramedia, which supplied the images for this article from its photo library www.floramedia-picture-library.com


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