Paulownia: The Fast-Growing Emperor Tree for Gardens

Many amateur gardeners dream of creating quick shade and enjoying spectacular flowers without introducing a rampant bamboo plant. This is exactly where a tree that is still surprisingly little known in Germany comes in: Paulownia, often called the emperor tree or foxglove tree. It combines rapid growth with a floral display that can transform the whole garden in April or May.

A tree that becomes a focal point within a few years

Paulownia is among the fastest-growing trees for gardens. In favourable conditions, a young tree can grow by around 1.5 to 2.5 metres each year. Within three years, it may already reach 5 to 7 metres in height, eventually growing to around 10 to 12 metres in most cases. That is an impressive result for a domestic garden.

It is characterised by a straight trunk and a broad, fairly open crown. Its leaves are large and heart-shaped, and on vigorous specimens can grow almost as large as a young child. They soon create a dense, pleasant area of shade, making the tree ideal beside a patio, seating area or children's play space.

“Paulownia delivers the pace of bamboo without spreading uncontrollably – a clear advantage for small plots.”

Unlike many types of bamboo, the emperor tree does not produce aggressive runners. There are no invasive rhizomes quietly travelling beneath the fence into a neighbour's garden. The tree remains where it is planted and can be kept under control easily with ordinary pruning.

Why Paulownia flowers turn gardens into a sea of purple clouds

Its grand display starts in spring. Before the first leaves emerge, the tree opens huge quantities of bell-shaped flowers. These appear in lavish panicles and range from soft lilac to violet and pale blue, depending on the variety.

Viewed from a distance, the crown can look like a pastel-coloured cloud floating above the trunk. Since there are no leaves at this stage, the flowers are especially prominent. The effect is more reminiscent of exotic ornamental trees in southern parks than of a conventional garden tree.

There is also a delicate fragrance, which many people describe as vanilla-like or gently sweet. Bees and other pollinators flock to the flowers, making the tree a valuable food source for insects.

“Anyone seeking an insect-friendly garden will find Paulownia a rapid supplier of nectar, pollen and structure.”

Choosing a site: where the emperor tree performs at full speed

The best position in the garden

Paulownia thrives on warmth and light. A position in full sun is best, while partial shade noticeably slows its growth. Sheltered sites are ideal, particularly in places that frequently experience cold easterly winds in spring.

The tree has certain soil preferences, although it is not overly fussy:

• deep, loose garden soil
• soil rich in organic matter, such as compost or leaf mould
• good drainage with no persistent waterlogging
• a moderate pH, ranging from slightly acidic to mildly alkaline

Heavy, permanently damp clay soils, or areas where puddles remain after rainfall, are considerably less suitable. In these situations, loosen the soil before planting and improve it with coarse sand and plenty of compost.

How to plant it properly

A thorough start is worthwhile for a young tree. As a guide, dig a planting hole measuring around 60 x 60 x 60 centimetres. Mix the excavated soil with 10 to 20 litres of well-rotted compost. This blend provides nutrients while keeping the soil structure open.

Gently loosen the roots before placing the tree in the hole. Then backfill with the mixture, firm it lightly and water generously: about 20 litres of water will help remove air pockets and settle the root ball securely. A mulch layer 5 to 8 centimetres deep prevents the soil from drying out and retains moisture for longer.

The first years: care makes all the difference

Watering, feeding and pruning

During its first two to three summers in particular, Paulownia needs regular watering until it has developed a deep root system. In dry spells, 10 to 20 litres per week is a useful guideline, applied over one or two watering sessions.

Once a year, ideally in early spring, the tree benefits from an additional nutrient boost. Around 10 litres of compost, spread loosely across the root area, is suitable. Mineral fertiliser is unnecessary and may even make the growth too soft and vulnerable.

There are two basic pruning approaches:

• Tree form: Prune back only lightly after flowering, removing dead or crossing branches. The aim is a stable, well-formed crown with plenty of potential flowering shoots.
• Giant-leaf option: Cut back hard in late winter to just a few buds. The tree will then produce only a few, exceptionally vigorous shoots with enormous leaves, but it will flower only sparsely.

Anyone wanting the spectacular cloud of flowers in spring should prune conservatively and carry out most cutting after flowering.

Protection against frost and cold

Paulownias are considered reasonably frost-hardy, but young trees can still be sensitive to severe sub-zero temperatures. In exposed locations, wrapping the trunk with horticultural fleece and adding a thicker mulch layer of 10 to 15 centimetres can help. The roots cope with cold better than the shoots and buds.

Late frosts in spring are particularly troublesome. Flower clusters develop early and may be damaged by overnight frost. In that event, the crown can initially appear bare or uneven in early summer. Once temperatures rise, the frost-damaged shoots can be cut out, and the tree will usually produce strong new growth, although with fewer flowers that year.

Risks, limitations and legal considerations

Self-seeding and spread

The emperor tree produces numerous very light seeds, which the wind can carry over some distance. In warm regions, these seeds may occasionally germinate on their own in cracks, on uncultivated ground or along paths.

To prevent this, cut off the seed heads before the capsules split open. Seedlings that emerge on your own property can be pulled up or dug out easily while they are still small.

Regional restrictions may apply

In some countries and particularly sensitive ecosystems, the species is monitored critically because it can spread more strongly under certain conditions. In central Europe, this is currently more of a local issue, for example near protected natural areas.

Before carrying out a larger planting scheme, such as planting several trees close to river floodplains, it is worth making a quick check with local authorities or conservation groups. This avoids conflict if special rules already apply in your area.

Paulownia varieties and uses in the garden

Several species and varieties are sold under the names Paulownia and emperor tree, with Paulownia tomentosa and Paulownia fortunei being the most widespread. They differ slightly in flower shape, colour and growth habit, but both are suitable for an ordinary domestic garden.

• Specimen planting: Leave 6 to 8 metres of clear space around the tree so that its crown can develop freely.
• Avenue or row planting: A minimum spacing of 6 metres between trunks provides adequate light and air.
• Rapid shade: In young gardens with no established trees, it quickly creates the impression of a mature, finished space.

As well as serving as an ornamental and shade tree, the emperor tree also produces timber. It is very light, relatively strong and dries quickly. In some countries, it is used for furniture, lightweight construction or musical instruments. This is usually of secondary importance in private gardens, but it demonstrates how versatile the plant is.

Practical tips for everyday gardening and design

Because Paulownia requires plenty of light, it is especially suited to modern, relatively open gardens with lawns, perennial borders and few tall woody plants. Many gardeners plant spring bulbs such as tulips or daffodils beneath its crown: they benefit from the early sunlight before the tree's leaves begin to cast shade.

For those wishing to support insects, combine the emperor tree with flowering shrubs such as cornelian cherry, serviceberry or butterfly bush. This creates a continuous food source for pollinators from March until late summer.

One point to allow for when planning: large leaves and numerous flowers also mean more organic matter in autumn. If you do not want to clear away the leaves constantly, simply leave them beneath the tree. There they break down and improve soil quality over time, creating a natural nutrient cycle.

For children, the tree is often a highlight: its huge leaves invite touching, its flowers look almost magical, and its rapid gain in height makes garden changes clearly visible. At the same time, once the tree is strong enough, the trunk generally remains smooth and suitable for climbing, adding another attraction to family gardens.