Tag Archive: invasive

paulownia-500x500So many trees beginning with ‘P’- which to choose? My choice is a tree that poses a dilemma- to prune or not to prune? If you do, you will encourage massive foliage which is a fabulously exotic addition to any garden. Alternatively, don’t and you get some wonderful flowers…the choice is yours.

Common name: Foxglove Tree, Empress Tree, Princess Tree

Native areas: Pawlonia tomentosa (syn. P. imperialis) is native to Japan and central and western China, where it has become virtually extinct due to a pathogen. It has become very common in North America, where it is considered an exotic invasive species. It was introduced to the UK in 1834.

Historical notes: The tree was named after Anna Pavlovna, daughter of Tsar Paul I and wife of Prince Willem of the Netherlands. In China, the tree is planted at the birth of a girl. The fast-growing tree matures when she does. When she is eligible for marriage the tree is cut down and carved into wooden articles for her dowry. Carving the wood of Paulownia is an art form in Japan and China. In legend, it is said that the phoenix will only land on the Empress Tree and only when a good ruler is in power. Several Asian string instruments are made from P. tomentosa.

The soft, lightweight seeds were commonly used as a packing material by Chinese porcelain exporters in the 19th century, before the development of polystyrene packaging. Packing cases would often leak or burst open in transit and scatter the seeds along rail tracks and near to ports. The magnitude of the numbers of seeds used for packaging, together with seeds deliberately planted for ornament, has allowed the species to be viewed as an invasive species in areas where the climate is suitable for its growth, notably Japan and the eastern United States.

Features: Paulownia tomentosa is an extremely fast-growing tree; its growth rings have been measured at three every inch. However the UK’s climate slows this down, and any growth under a pencil thickness generally succumbs to winter frosts, and which in turn contribute to its overall broadness. It will ultimately grow to 10–25 m (33–82 ft) tall, with large heart-shaped to five-lobed leaves 15–40 cm (6–16 in) across, arranged in opposite pairs on the stem. On young growth, the leaves may be in whorls of three and be much bigger than the leaves on more mature growth. The leaves can be mistaken for those of the Catalpa.

The very fragrant flowers are formed in autumn and then open in spring before the leaves in early spring (May), on panicles 10–30 cm long, with a tubular purple corolla 4–6 cm long resembling a foxglove flower. However, if there is a prolonged period where winter temperatures fall below minus 5 degrees celsius, no flowers will develop the following spring.The fruit is a dry egg-shaped capsule 3–4 cm long, containing numerous tiny seeds. The seeds are winged and disperse by wind and water. Pollarded trees do not produce flowers, as these only form on mature wood. A mature tree in its native environment can produce up to 20 million seeds a year!

Uses: P. tomentosa is cultivated as an ornamental tree in parks and gardens. It has gained the RHS Award of garden Merit (AGM). The characteristic large size of the young growth is exploited by gardeners: by pollarding the tree and ensuring there is vigorous new growth every year, massive leaves are produced (up to 60 cm across). These are popular in the modern style of gardening which uses large-foliaged and “architectural” plants. Alternatively it can be grown for its attractive, fragrant flowers.

Growing conditions: a fast growing, medium to large tree, it does best in a sunny, reasonably sheltered site, preferably in moist, humus-rich, fertile soils. Protect young trees from frost. Can be pollarded. Very tolerant of atmospheric pollution.

Paulowni_imperialis_SZ10Further information:


RHS- Pawlonia tomentosa

Barcham trees directory- Pawlonia tomentosa

Old School Gardener

Rhododendron viriosum - picture by Brian Walters

Rhododendron viriosum – picture by Brian Walters

Just about now many of the heritage gardens of Britain are coming alive with Rhododendron colour. Rhododendron is named from the ancient Greek words for  “rose” (rhódon)  and “tree” (déndron). It is a genus of over 1000 species of woody plants in the heath family, and are either evergreen or deciduous. Most species have showy flowers. Rhododendrons are extensively hybridized in cultivation, and natural hybrids often occur in areas where species ranges overlap.They were introduced to the UK in the late 18th century from the Himalayas and China.

There are over 28,000 cultivars of Rhododendron in the International Rhododendron Registry held by the Royal Horticultural Society. Most have been bred for their flowers, but a few are of garden interest because of ornamental leaves and some have ornamental bark or stems. Recent genetic investigations have caused an ongoing realignment of species and groups within the genus. Horticulturally, rhododendrons may be divided into the following groups:

  • Evergreen rhododendrons: the main category

  • Vireya (Malesian) rhododendrons: these are tender shrubs

  • Azaleas (a section of generally small-sized, small-leaved and small-flowered shrubs), further divided into deciduous and evergreen hybrids. They are distinguished from “true” rhododendrons by having only five anthers per flower.

  • Azaleodendrons – semi-evergreen hybrids between deciduous azaleas and rhododendrons

Rhododendron luteum

Rhododendron luteum

Species names include:

R. arborescens = tree like

R. augustini = after Dr. Augustine Henry, famous 19th /20th century irish plantsman.,

R. balsamiaeflora = balsam-flowered, the double flowered florist’s balsam.

R. campanulatum = bell – shaped flowers

R. campylocarpum = bearing bent fruits

R. cinnarbarinum = cinnabar red

R. decorum = shapely or becoming

R. fastigiatum = fastigiate or erect branches taperign to a point

R. flavum = yellow (also known as R. luteum)

R. impeditum = twiggy branches

R. laponicum = of lapland

R. molle = soft or velvety, refering to the leaves

R. myrtilloides = myrtle – like

R. nudiflorum = naked flowered, i.e coming before the leaves

R. ponticum = Pontic, a  region of the Black Sea

R. rhodora = old generic name signifying rosy-red

R. russatum = reddened- the foliage

R. sutchense = from Szechuan

R.vaseyi = discovered by Mr. G.R. Vasey, 19th century botanist

R. viscosum = sticky or viscous

R. yunnanense = of Yunnan, southern China

Rhododendron ponticum

Rhododendron ponticum

The rhododendron is the national flower of Nepal, where the flowers are considered edible and enjoyed for their sour taste. The pickled flower can last for months and the flower juice is also marketed. The flower, fresh or dried, is added to fish curry in the belief that it will soften the bones!

Some species of rhododendron are poisonous to grazing animals because of a toxin in their pollen and nectar. Rhododendron is extremely toxic to horses, with some animals dying within a few hours of ingesting the plant.

People have been known to become ill from eating honey made by bees feeding on rhododendron and azalea flowers. Xenophon described the odd behavior of Greek soldiers after having consumed honey in a village surrounded by Rhododendron ponticum during the ‘March of the Ten Thousand’ in 401 BC.Pompey’s soldiers reportedly suffered lethal casualties following the consumption of honey made from Rhododendron deliberately left behind by Pontic forces in 67 BC. Later, it was recognized that honey resulting from these plants has a slightly hallucinogenic and laxative effect., the suspect rhododendrons being R. ponticum and R. luteum (also known as R. flavum). Eleven similar cases have been documented in Turkey during the 1980s. The effects of R. ponticum was mentioned in the 2009 film Sherlock Holmes as a proposed way to arrange a fake execution.

Rhododendron 'Lemon Dream'

Rhododendron ‘Lemon Dream’

Rhododendrons are grown for their spectacular flowers, usually borne in spring. Some also have young leaves and stems covered in a striking dense woolly covering (indumentum) and some – the deciduous rhododendrons or azaleas – have good autumn colour. Some species (e.g. Rhododendron ponticum in Ireland and the United Kingdom) are invasive plants, spreading in woodland areas replacing the natural understory. R. ponticum is difficult to eradicate, as its roots can make new shoots.

Sources and further information:


BBC video of Rhododendrons in the Himalayas

RHS- growing Rhododendrons

Royal Botanic Garden, Edinburgh – Rhododendron collection

Quizzicals: answers to the two clues given in Plantax 10…

  • Evader of women – Ladies Slipper
  • Oriental busybody – Japanese Medlar

..and 2 more cryptic clues to the names of plants, fruit or veg…

  • Where policemen spend their holidays
  • Feline relative

(thanks to Les Palmer, answers in the next Plantax!)

Old School Gardener

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Ranunculus asiaticus - Persian Ranunculus

Ranunculus asiaticus – Persian Ranunculus

Yesterday was sunny but breezy, so my wife and I and two friends went out for a delightful walk in the local countryside, followed by Sunday lunch at a local pub. On the walk we came across signs to a ‘bluebell event’ and passed by the house and garden where this was taking place, but alas, could not spot any but a couple of rather weak looking bluebell blooms. Having been attracted out to another such event publicised a week or so ago (when in a ‘normal’ spring the Bluebells should have been well into flower) and been disappointed, I was skeptical that there was any real show on offer, especially as the bluebells at ‘Old School Garden’ were nowhere to be seen other than making a few clumps of lush foliage!

So, the late spring was once again (not) in evidence! We did, however, see some patches of Wood Anemone (Ranunculus nemorosus, meaning found in groves) amongst larger swathes of Lesser Celandine (Ranunculus ficaria, meaning fig like, referring to the heart- shaped leaves), that reliably invasive yellow – flowered creeper. According to Gilbert White, the famous diarist writing around 1800, the Lesser Celandine flowers came out on February 21, but it is more commonly expected between March and May these days, and is sometimes called the “spring messenger”.

Ranunculus ficaria, Lesser Celandine

Ranunculus ficaria, Lesser Celandine

The name Ranunculus comes from the latin for “little frog,” (rana = frog and a diminutive ending). This probably refers to many species being found near water –  just like frogs! It is a large genus of about 600 species in the similarly named family Ranunculaceae. Members include buttercups, spearworts, water crowfoots as well as the lesser Celandine. According to the Oxford English Dictionary, Celandine comes from the latin chelidonia, meaning swallow: it was said that the flowers bloomed when the swallows returned and faded when they left. The common name Celandine is used to describe three different plants; as well as Lesser Celandine (a Ranunculus) there is Greater Celandine (Chelidonium majus, in the poppy family) and the Celandine Poppy (Stylophorum diphyllum, also in the poppy family).

Ranunculus glacialis

Ranunculus glacialis

Ranunculus repens or Creeping Buttercup

Ranunculus repens or Creeping Buttercup

Other Ranunculus species names are:

R. aconitifolius = aconite (aconitum) – like leaves

R. acris = sharp or bitter – the Meadow Crowfoot or Buttercup, a double flowered variety is grown in gardens

R. amplexicaulis = leaves, stem clasping

R. anemonoides = anemone – like

R. asiaticus = Asian, the Persian Ranunculus

R. crenatus = leaves crenated or scalloped

R. glacialis = icy, a high alpine plant

R. gramineus = grassy – the leaves

R. lingua = a tongue – the shape of the leaves

R. lyallii = after David Lyall (a 19th century Scottish botanist), the Rockwood or Mount Cook Lily

R. nivalis = snowy, or lofty regions

R. nyssanus = from Nyssa (an ancient city in Turkey)

R. parnassifolius = leaved like Parnassia

R. repens = creeping or crawling, the Creeping Buttercup

R. rutaefolius = rue (Ruta) – leaved

Most Ranunculus are herbaceous perennials, with bright yellow or white flowers (if white, they still come with a yellow centre), though some are annuals or biennials. A few species have orange or red flowers. There are usually five petals, but sometimes six, numerous, or none, as in R. auricomus. The petals are often highly lustrous, especially in those with yellow flowers (e.g buttercups).

Ranunculus lyallii- the Mount Cook lilly

Ranunculus lyallii– the Mount Cook lily

A forming Ranunculus fruit or seed head (achene)

A forming Ranunculus fruit or seed head (achene)

Buttercups usually flower in the spring, but flowers may be found throughout the summer, especially where they are unwelcome garden weeds! The name buttercup may derive from a false belief that the plants give butter its characteristic yellow hue (in fact it is poisonous to cows and other livestock). A popular children’s game involves holding a buttercup up to the chin; a yellow reflection is supposed to indicate a fondness for butter!

In the interior of the Pacific Northwest of the United States the buttercup is called “Coyote’s eyes”. In the legend behind this the Coyote was tossing his eyes up in the air and catching them again when the Eagle snatched them. Unable to see, Coyote made eyes from the buttercup!

Ranunculus' Double Orange'

Ranunculus’ Double Orange’

Ranunculus ficaria 'Brazen Hussy'

Ranunculus ficaria ‘Brazen Hussy’

Ranunculus species are used as food plants by the larvae of some butterflies. Some species are popular ornamental flowers, and many cultivars have large and brightly coloured flowers. When Ranunculus plants are handled, a naturally occurring substance, ranunculin is broken down to form a toxin known to cause dermatitis in humans and care should therefore be taken when handling large numbers of the plants. The toxins are degraded by drying, so hay containing dried buttercups is safe.

The Lesser Celandine plant used to be known as Pilewort because it was used to treat haemorrhoids. Supposedly, the knobbly tubers of the plant resemble piles, and according to the ‘doctrine of signatures’ this resemblance suggests that Pilewort could be used to cure piles! The German vernacular Scharbockskraut (“Scurvyherb”) derives from the use of the early leaves, which are high in vitamin C, to prevent scurvy. The plant is widely used in Russia and is sold in most pharmacies as a dried herb.

A woodland floor of Lesser Celandine

A woodland floor of Lesser Celandine

Further information:


Planting guide

Growing Ranunculus

Ranunculus ficaria ‘Brazen Hussy’


answers to the two clues given in Plantax 9…

  • Substandard animal limb = Pawpaw
  • West Indies batsman + Food superstore = Vivaldi

..and 2 more cryptic clues to the names of plants, fruit or veg…

  • Evader of women

  • Oriental busybody

(thanks to Les Palmer, answers in the next Plantax!)

Old School Gardener

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Euphorbia characias sub species 'Wulfenii'

Euphorbia characias sub species wulfenii

A bit like Marmite, gardeners  seem to either love or hate Euphorbia (Spurge) – I love them!

This is a large genus of over 2,000 species, including annuals,perennials as well as shrubs and succulents. They originate from many different parts of the world and as a result their growing requirements differ widely. They include the red-leaved species commonly seen at Christmas, Euphorbia pulcherrima (Poinsettia)

Euphorbia pulcherrima (Poinsettia)

Euphorbia pulcherrima (Poinsettia)

Some are evergreen and hardy, others are semi evergreen or deciduous. Nearly all species have distinctive ‘cyathia‘- small cups of long – lasting bracts that can be green, yellow, red, brown or purple. These are ‘cupping nectaries’ containing insignificant flowers with much reduced parts. In the perennials and shrubs these cyathia are carried in dense clusters. The leaves are very varied  and often are shed quite quickly.

Some species are very invasive and are not really suitable for the garden (e.g. E. cyparissias and E. pseudovirgata) others will self seed prolifically so need to be used with care (e.g. E. lathyris, E. hybernia,E.coralloides and E.wallichii). Some species can be invasive in some climates (e.g. E. myrsinites in parts of the USA) but are less problematic in milder, wetter places.

Euphorbia cyparissias (Cypress Spurge)

Euphorbia cyparissias (Cypress Spurge)

Euphorbia myrsinites

Euphorbia myrsinites

All Euphorbias resent disturbance, so siting them carefully from the start is important for long lasting plants. Euphorbia suit every situation from desert to bog, formal courtyard to wild woodland. With a couple of  exceptions Euphorbia are easy to grow. They are also look great in the garden, the colourful bracts lasting many weeks.

Euphorbia look best if allowed to sprawl at will, but if space is limited, you may need to support the floppier ones.

The evergreens require no routine pruning – simply tidy them up when they start to look untidy. Deciduous ones should be cut down to ground level in autumn. New shoots will emerge from the crown in spring. The biennial forms such as E. characias produce new shoots from the base each year. Cut out dead stems in winter. They are not fussy as to soil, but most prefer good drainage.

The bigger, more sculptural forms look good with architecture – against steps or walls, or in corners of courtyards. E. mellifera is a superb statement plant. E. myrsinites can be used in raised planters to sprawl over the sides. E. griffithii ‘Fireglow’ looks great beside water, with bronzy Rodgersias and red-flushed Astilbes, but will also look good in a hot border, while E. ‘Whistleberry Garnet’ associates well with ferns, Hostas and the dark-patterned leaves of Geranium phaeum.

All parts of Euphorbia are useful in flower arranging either in the fresh or dried state.

However all Euphorbia are poisonous and bleed a skin irritant milky sap, whereas the flowers are highly allergenic, so be careful when cutting or handling these wonderful plants.

Euphorbia polychroma

Euphorbia polychroma

Euphorbia griffithii 'Fireglow'

Euphorbia griffithii ‘Fireglow’

Euphorbia characias sub species 'Wulfenii'

Euphorbia characias sub species wulfenii

Further information:

National Collection of hardy Euphorbias

Growing Euphorbias

Euphorbia pulcherrima (Poinsettia)

Common varieties


Old School Gardener

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