<em>Paulownia</em>, empress tree: planting, cultivation and care

Description and botany

Formerly belonging to the large family Scrophulariaceae or Scrofulariaceae, Paulownias now make up their own botanical family: Paulowniaceae. The genus includes six species Paulownia catalpifolia, Paulownia kawakamii, Paulownia elongata, Paulownia X taiwaniana, Paulownia fortunei and the best-known Paulownia tomentosa (formerly called Paulownia imperialis), nicknamed “Imperial tree”.

All are very similar, but almost exclusively in cultivation one finds only Paulownia tomentosa and Paulownia fortunei, the latter distinguished from its cousin by flowering about three weeks earlier.

All these species are native to Asia, more precisely to mountains of China and Korea. They are pioneer trees that colonise fallow or disturbed ground first, to “prepare the ground” for other plants. It is this pioneering character that has made Paulownia tomentosa invasive in parts of North America. Later, in its natural environment, thanks to its soil-preparing activity, other tree species move in and grow quickly, creating too much shade that proves fatal to the Paulownia.

It was introduced long ago into Japan and is now cultivated worldwide, notably for its tolerance of pruning and pollution.

Paulownia tomentosa (syn. imperialis) – botanical illustration

Reaching up to twenty metres in its native range, Paulownia rarely exceeds twelve metres in our gardens. Which is already quite impressive. It is a majestic tree with a straight trunk and a spreading dome-shaped crown, ideal for summer shade.

Bark is grey, smooth and slightly striate. Small orange vesicles can be seen on young trees.

Twigs are pubescent, that is covered with hairs, and bear on long petioles large deciduous opposite leaves about 25 cm, heart-shaped with silky underside. This gave the species name of P. tomentosa: “tomentose” meaning “silky”. Older shoots become hollow. Do not be surprised when pruning them!

Foliage turns yellow in autumn before dropping quickly. From autumn, the flower buds on the twigs can be seen, reddish in colour.

Flowering occurs in spring, generally before leaves appear. Hermaphrodite flowers, arranged in erect panicles at shoot tips, are purple and fragrant. The resulting fruits are oval, pointed capsules that remain decorative all winter. They open at ripeness to release hundreds of cotton-like winged seeds.

Sexual maturity of Paulownia is reached at around twenty-five years, but the tree lives only about a hundred years. Paulownia is a fast-growing species, increasing by 4 to 7 m in just three years.

The tree has a fairly dense root system that helps reduce soil erosion and stabilise banks.

Paulownia tomentosa: flower buds, flowers, fruits and huge leaf

Main species and varieties

Paulownia tomentosa - Foxglove Tree

Type species Paulownia tomentosa becomes a large tree, easily reaching 12 m in height but, when pruned into coppice shoots, can be kept to bush size. Leaves then take on impressive proportions but, sadly, flowering is lost...

• Flowering time June, July
• Height at maturity 12 m

See the product sheet

Paulownia fortunei Fast Blue Minfast - Foxglove Tree

Paulownia fortunei has a very slender, almost conical habit. It will therefore occupy less space than its cousin P. tomentosa in the long term while retaining generous foliage and magnificent spring flowering.

• Flowering time June, July
• Height at maturity 8 m

See the product sheet

Planting Paulownia

Where to plant?

Paulownia thrives in rich, humus-bearing, fresh, well-drained and deep soil. An exposure in full sun suits it perfectly, but it can also succeed in partial shade. To flower well, it nevertheless needs long, warm summers, but not too dry.

As this tree already produces its flower buds in autumn and flowers early in the season, it is advisable to protect it from cold winds and severe frosts that can destroy the flowering.

Indifferent to soil pH.

When to plant?

Paulownia is best planted in autumn or early spring. It is always possible to plant outside these periods, but watering will need to be monitored. Do not plant during a heatwave or during frost!

How to plant?

• Plunge the pot of your new Paulownia into a bucket of water for a few minutes to re-moisten the root ball
• Dig a hole twice as deep and twice as wide as the root ball
• Throw one or two handfuls of well-rotted compost into the bottom of the hole
• If your soil is heavy, you can add some gravel to improve drainage
• Loosen the root ball a little to free the roots. Do this carefully by hand or with a small hand fork to avoid damaging the roots
• Place the rest of the root ball at the bottom of the hole, spreading the roots well
• Fill the hole with the excavated, loosened soil
• Firm the soil gently around the tree with your hands (not with your feet!)
• Give 10 litres of water at the base with a watering can to reduce the risk of ‘air pockets’ between the roots and the soil
• Apply a mulch to protect the young tree from drought or plant directly at the base some small groundcover plants (creeping bugle, sweet woodruff, Glechoma, Geranium macrorrhizum, …)

→ Find out more in our tutorial How to plant a Paulownia?

Maintenance, pruning and care

Protection from cold

Young shoots and flower buds can be damaged by late frosts or cold, dry wind. Best to find a sheltered spot in the garden or cover with a winter fleece during the tree’s early years.

Pruning

Just before growth resumes, between February and the end of March, you can prune diseased or dead wood and remove a few branches that detract from the tree’s structure and habit. Always keep in mind that cutting large-diameter branches weakens trees. So be light with the saw and pruning shears!

At the same time, if you wish to keep your Paulownia to a modest bush size, you can cut all the branches back, leaving only 2 or 3 buds at the base. The tree will then have a bushy habit with even larger leaves, but, sadly, you will not enjoy the flowering.

→ Learn more about pruning Paulownia in our tutorial!

Possible diseases

Paulownia is very resistant to pollution and parasitic pests, but in very damp conditions, especially in summer, it can show some signs of disease: cankers, rot, foliar spots, but above all powdery mildew should be watched for, though still relatively rare. In poorly drained soil, an attack by honey-coloured Armillaria, a wood-rotting fungus that kills trees, may also occur.

→ Learn more about diseases and parasitic pests of Paulownia in our care sheet!

Propagation

By sowing

Paulownia, with its pioneering character, reproduces readily by sowing. Seeds need a period of cold to be able to germinate. Therefore, either sow seeds outdoors in autumn, or place them in a tray in the fridge (5°C) for a few weeks to sow them in spring afterwards. You can sow them one per pot or in rows outdoors then pot up the young seedlings later (keep the strongest specimens!) and only plant them permanently outdoors the following autumn.

Can’t find Paulownia seeds? We thought of you with Paulownia tomentosa seeds available to order online.

Separating suckers

Sometimes the tree produces suckers. All you need to do is dig carefully at the base of the tree to free the sucker. Cut the root that still holds it to the parent plant then pot up for planting outdoors in autumn.

→ For everything about your favourite bush suckering, read My bush is suckering: why? What should I do?

By cutting

Paulownia propagation by cuttings is carried out in autumn using root cuttings. Ideally, find by digging at the base of the tree a root that has rootlets. Place this piece of root on a mixture of sand and potting compost and keep warm (20°C) and in darkness. At the very start of spring, the first leaves will appear; you can then pot up and wait until the following autumn to plant outdoors.

You can also take a cutting in summer from a young shoot about ten centimetres long into a light substrate (potting compost + sand) and keep it under cover. Place the shoot, having first cut back two-thirds of its leaves, into the compost. Cover with a plastic bag or the base of a plastic bottle to retain heat and humidity. The first new leaves should appear quickly, sign of good take. Plant out only in the following spring or autumn.

Some people have success rooting cuttings in water! So why not try: place a young shoot in a vase filled with water with a piece of charcoal (to prevent rotting; otherwise change the water every two days). As soon as the first small roots appear, pot the seedling into a pot and a light substrate (potting compost + sand). Do not let roots develop too much, they will be too fragile to grow afterwards. You can plant your tree out in the following spring or autumn.

→ Find out more in Alexandra’s tutorial: How to propagate Paulownia?

Incorporating Paulownia into the garden

A grove of bushes with spring flowering

Le Paulownia tomentosa produces purple flowers in April. Ideal companion would be a lower bush in a tone that complements it, such as the uncommon Syringa x persica var. laciniata with lilac flowers and beautiful laciniate foliage. To introduce contrast with the purple, try yellow and orange flowers, for example the charming but sadly seldom planted Weigela middendorffiana, a small weigela with lovely pale yellow to amber flowers. Pair it with a Forsythia koreana ‘Kumsun’, a very small, hardy forsythia that blooms bright yellow in spring and whose leaves take on a granulated appearance thanks to fine cream-white veins. Complete the group with a Cornus mas ‘Jolico’ which, as well as offering a lovely yellow flowering in spring, will provide large edible red cornels in autumn, a colour that will echo Paulownia’s floral buds perfectly.

An example of a grove association: Paulownia tomentosa, Forsythia koreana ‘Kumsun’, Syringa persica ‘Laciniata’, Cornus mas ‘Jolico’ and Weigela middendorffiana

Pair your Paulownia with a beautiful climbing plant

If your Paulownia fortunei ‘Fast Blue’ is already tall and well established, you could echo its colour with a wisteria that will flower at the same time and in the same tones, such as Wisteria venusta ‘Okoyama’, a light, delicate wisteria that will not smother your Paulownia.

You can also play on a strong contrast by training a liana with yellow or even orange flowering. In that case, and if your Paulownia is in a spot protected from frost, consider a striking trumpet vine with orange and yellow flowers such as Campsis capreolata ‘Tangerine Beauty’.

An example of an association with a climbing plant like trumpet vine ‘Tangerine Beauty’

A mass of gigantic leaves in rich, moist soil

If you love exuberant, lush foliage, you can coppice your Paulownia tomentosa every year. It will then produce enormous leaves! Pair it with a Catalpa bignonioides ‘Aurea’, also coppiced, with magnificent golden-yellow foliage whose leaf shape echoes that of the Paulownia. Add a large, imposing Astilboides tabularis with substantial leaves and airy flowering, as well as a Fatsia japonica, an enduring classic of lush gardens. If you have a little room at the edge, plant some Hosta ‘Empress Wu’, huge hostas with slightly bluish foliage that will contrast beautifully with that of the catalpa.

→ Discover 5 other great pairing ideas with Paulownia in our advice guide!

An example of an association of luxuriant foliage: Paulownia tomentosa, Fatsia japonica, Catalpa bignonioides ‘Aurea’, Astilboides tabularis and Hosta ‘Empress Wu’

Did you know?

• The name was given in honour of Anna Pavlowna, daughter of Tsar Paul I.
• Previously in China, a Paulownia was planted when a girl was born. The tree grew and was eventually felled at her wedding so its wood could form part of her dowry.
• Since the 11th century, Paulownia, together with the phoenix, has been used as a symbol on clothing of the Chinese Imperial household.
• Viscount de Cussy brought the first Paulownia seeds to the Jardin des Plantes in Paris in 1834. The tree flowered for the first time in 1842 and died in 1956… only to be quickly replaced by a young specimen of the same species.
• Even today in Japan, Paulownia leaves represent an emblem that honours deserving individuals, as well as the Japanese Prime Minister and his government.
• Paulownia is still used for its wood in China for cabinetmaking and luthiery.
• It is widely used in agroforestry, because the leaves are rich in nitrogen and can therefore be used as fodder or as mulch. However, they compost rather poorly.