By Miranda Kimberley Friday, 29 March 2013
These fast-growing trees are prized for their timber as well as being popular ornamentals, says Miranda Kimberley.
Paulownia is the fastest-growing tree in the world. This makes it a highly prized timber tree and its lightweight wood is used worldwide to make furniture. But its vigorous growth can also be harnessed for ornamental purposes.
By cutting a P. tomentosa Award of Garden Merit (AGM) specimen down in the springtime, gardeners can produce a vigorous shoot that can grow up to 3m tall as well as attractive fresh green leaves up to 60cm across.
If left as nature intended, these six species of East Asian trees can become grand specimens, between 10m and 30m tall. They produce flowers that resemble those of a foxglove in shades between white and purple. They have large, heart-shaped leaves up to 30cm across that are often downy or hairy.
The only paulownia commonly grown in the UK is P. tomentosa AGM. It will become a handsome large tree, usually reaching up to 12m tall in our climate. In early spring, it produces panicles of highly attractive pale-violet flowers. The flowers buds begin to form before the winter and the flowers open before the leaves appear, so there is often danger of frost damage to flowers and new shoot tips. But established trees will react well to this, producing vigorous replacement shoots.
P. elongata holds the record for the fastest-growing tree species in the world. Like tomentosa, it is quite tolerant of a range of temperatures but is not as suited to ornamental gardens because of its upright growth. It is used more as a timber tree and as a tool in restoring deforested areas or sites suffering from erosion.
P. fortunei and its hybrids with P. tomentosa AGM are more likely to be used in parks and gardens.
P. fortunei is similar in habit to P. tomentosa. It has leaves around 12cm across that are downy on their underside. Its flowers are produced in a compact panicle and are creamy white, flushed lilac and heavily marked with purple inside.
The genus cannot be said to be tender - in fact, once established they tend to produce regenerative growth if knocked back by frosts. Their problem is that they come from climates where they receive more sun to harden their wood. Their vigour means they continue to grow into the colder season and they produce flower buds going into the winter. This means that young shoots and flower buds get frosted, which can be harmful for young plants. Ways around this include planting semi-mature trees, which are able to bounce back from frost damage.
To give them the best chance, plant them in a sheltered area out of cold, exposed winds. If possible, cut back frosted shoots to good buds, but this is not necessary on more mature plants because regeneration will occur naturally.
Another feature to be aware of is that flowers often appear towards the top of the tree, so when choosing a site an ability to view the tree from above is ideal. Other than those tips, paulownia is not a fussy tree. They need a position in full sun if possible and cope in a variety of soils, but a deep, moist loam is preferred.
What the specialists say
- Hossein Arshadi, amenity director, Hiller Nurseries, Hampshire
"Paulownia are fabulous trees, grown for their shade, flower and interesting shape. It's not a regular shape - instead their branches take twists and bends, which only adds to their attractiveness.
"Local authorities use them in parks and occasionally on streets, but I think more should be used as street trees - obviously not on smaller roads but they could be used on streets that are large enough to grow London planes, limes or tulip trees.
"Paulownia can also be cut back to a stool and then it will shoot vigorously from it, by up to 2m in a year. This keeps it at a manageable size and it will produce massive leaves, two-to-three times bigger than the normal size. You have to sacrifice the flower though.
"One of the things to watch out for with paulownia is that while it is a pretty hardy mature tree, its young shoot tips can get frost damage easily. That's why I would recommend customers plant older trees, because they are better able to cope with this damage and produce regenerative growth. They like a position in full sun and survive on any type of soil."
- Joanne McCullock, partner, Larch Cottage Nurseries, Cumbria
"We grow four different type of paulownia, which include the most commonly grown species, tomentosa. But we also grow catalpifolia, elongata and imperialis.
"To be honest, they are not a popular tree with customers. This is perhaps because our climate up north is a bit tricky for them, as I think they probably need a more continental climate to perform, with cold but dry winters. We had one planted in the garden that grew rapidly to around 5m but then it was killed three winters ago in the severe freezing conditions.
"In the correct conditions, they are beautiful and slightly exotic looking trees, with their foxglove-like showy flowers. At our nursery we grow paulownia quite easily from seed and quickly, with the protection of a polytunnel. In the polytunnel they do well, but outdoors they are more difficult. To give them the best chance in our area they should be given a sunny sheltered site."
- Shelley Mosco, managing director, Green Graphite, London
"As a mature tree, paulownia suits parks and larger landscapes. It forms a beautiful, spreading tree. But it can be maintained in a very different way, which involves cutting it down every year, pruning it so hard that it produces lush, giant leaves, of which I am in awe.
"So if I was to specify paulownia it would be in this stooled form, probably for a walled garden or an urban garden, with a slightly warmer climate, as part of a tropical planting style. I would plant the paulownia alongside bamboos, so that when it was cut down it wouldn't look so bare. Something like Phyllostachys nigra would look amazing next to it - the black stems against the lime-green new leaves."
Species and varieties
- P. catalpifolia is a rare species that is the result of a cross between the species tomentosa and elongata. All paulownia have large, heart-shaped leaves that are similar to catalpa leaves, but these most resemble them. They produce foxglove-like flowers that are between lavender and white.
- P. elongata is a very rare species in cultivation. It is the fastest-growing species. It has light-blue flowers with yellow centres and even larger leaves than tomentosa. It can withstand temperatures down to -15 degsC, though frost can still damage young shoots. Height: up to 20m.
- P. fortunei is a rarely seen species, similar in habit to tomentosa. Its flowers are fragrant, creamy-white, flushed lilac and heavily marked with purple on the insides. Height: up to 20m.
- P. fortunei Fast Blue = 'Minfast' is a highly floriferous variety that produces upright panicles of fragrant funnel-shaped flowers that are pinkish lilac on the outside and have yellow marks inside. This species is notable for its pyramidal, nearly fastigiate crown.
- P. kawakamii is a smaller tree than elongata or fortunei, reaching a mature height of 10m rather than 20m. The flowers are sapphire blue with a yellow centre. Height: 10m.
- P. tomentosa AGM (H3) is the most commonly grown paulownia in cultivation, partly because it is tolerant of pollution. It becomes a broad, round-topped tree and produces large, heart-shaped, bright-green downy leaves and fragrant, mauve-pink flowers in late spring. It is a fast-growing tree and many gardeners like to prune it hard annually to develop a bushy plant with even larger leaves than normal. Height: 12-18m. Spread: 10m.
- P. tomentosa 'Coreana' is a beautiful large tree that has wooly-backed, yellow-tinted leaves and large pyramidal inflorescences with violet flowers that are heavily spotted within. Height: to 20m.
Thank you to Floramedia, which supplied the main image for this article from its photo library
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