Many keen gardeners want shade quickly, but don’t fancy paving over half the plot with rampant bamboo. That’s where a tree comes into its own that, in Germany at least, still flies under the radar for surprisingly many people: the Paulownia - also known as the Empress tree, Kaiserbaum, or bluebell tree (Blauglockenbaum).
The tree that grows at bamboo speed
Paulownia is among the fastest-growing ornamental trees you can plant. In the right conditions, a young tree can put on an impressive 1.5 to 2.5 metres a year. After just three years, 5 to 7 metres is realistic, and mature trees commonly reach 10 to 12 metres.
Despite the pace, its shape remains neat and readable: a single, continuous trunk topped by a broad crown. In summer, the huge, heart-shaped leaves quickly create a dense, pleasant patch of shade - ideal beside a patio, seating area, or children’s play space.
“The Kaiserbaum delivers bamboo speed - but without runners that take over the garden.”
Unlike many bamboo types, Paulownia doesn’t send aggressive rhizomes shooting off in every direction. It stays where you plant it. That makes it far easier to control, particularly in smaller gardens, and you can forget about costly rhizome barriers.
A cloud of blossom in spring: why Paulownia stands out
Its real show begins in spring. Before any leaves appear, the crown is covered in dense panicles of bell-shaped flowers. Depending on the variety, colours range from soft lilac to deep violet, sometimes with a subtle bluish tinge.
From a distance, the canopy can look as though it’s been wrapped in pastel cotton wool. Anyone who has seen one in full flower rarely forgets it. There’s also a light fragrance, which can be reminiscent of vanilla or lilac.
For insects, Paulownia is a real draw. The blossoms produce plenty of nectar, giving bees and butterflies an early, generous food source in spring.
“If you want to support bees in your garden, Paulownia is a true spring buffet for pollinators.”
Location and planting: getting the Kaiserbaum off to the right start
Choosing the right spot in the garden
To make the most of its growth potential, the tree needs one thing above all: sun. A position in full sun, ideally sheltered from bitter, funnelled winds, gives the best results.
- Light: sunny to full sun
- Soil: deep, humus-rich, free-draining
- No waterlogging: avoid pots or hollows where water sits
- Room up and out: keep at least 6–8 metres from the house, neighbours, and other trees
The soil should be loose so the roots can quickly drive downwards. If you have heavy clay, it’s worth working in sand and plenty of compost.
Preparing the planting hole
For a strong start, it’s best to dig a generous planting hole of about 60 x 60 x 60 centimetres. Mix the excavated soil with 10 to 20 litres of well-rotted compost. Return this mix to the hole, set the tree in place, firm the soil lightly, and water thoroughly straight away - around 20 litres, so the rootball connects properly with the surrounding soil.
A mulch ring around the trunk, 5 to 8 centimetres thick, helps retain moisture and keeps weeds down. Bark mulch, woodchip, or leaves all work well.
“If you’re generous in the first hours after planting, you’ll save yourself plenty of problems later with drought and stability.”
Care in the first years: water, pruning, protection
Watering and root development
Consistent watering is crucial, especially through the first two to three summers. Depending on the weather, 10 to 20 litres a week may be needed. Water less often but more deeply, rather than adding a few splashes every day. That encourages roots to push down into the soil instead of lingering near the surface, where it dries out quickly.
Pruning for a shapely crown and plenty of flowers
After flowering, you can influence how the crown develops. Light pruning helps keep a balanced shape and encourages strong shoots that will set lots of flowers again the following year. Dead or damaged wood should be removed without hesitation.
In very exposed locations, it can be sensible to keep young trees a little lower at first and prune more firmly, so they build a stable framework.
Protection from frost and late cold snaps
The buds form relatively early in the year. Late night frosts can damage them, which may mean fewer flowers - or none at all - that season. Young trees are more sensitive than established ones.
- Wrap young trees with horticultural fleece on frosty nights
- Increase the winter mulch layer to 10–15 centimetres
- After frost damage, cut back frozen shoot tips once the cold spell has passed
In many cases, the tree will then reshoot strongly. Paulownia is generally considered robust, but it does appreciate extra attention in its first winters.
Risks and limitations: not effortless everywhere
Keep an eye on self-seeding
Paulownia produces large numbers of seeds that can be carried by the wind. In warmer areas, young plants can establish beyond your own boundary. In some countries, there is now discussion about whether certain varieties could spread uncontrollably.
If you want to play it safe, check under and around the tree regularly and remove seedlings while they are still easy to pull out. In ecologically sensitive areas, it’s worth a quick call to your local nature conservation authority to see whether any restrictions apply.
Don’t underestimate the space it needs
As tempting as fast growth is, this tree is only a partial fit for a tiny terrace-house garden right on the boundary. The crown needs air and the roots look for room. Planning too tightly can lead to neighbour disputes and expensive tree work later.
“Before planting, it pays to look 15 years ahead - how big is the tree really allowed to become?”
Popular varieties and ideas for using it in the garden
In the trade, two species crop up time and again: Paulownia tomentosa and Paulownia fortunei. They differ slightly in flower colour, leaf size, and vigour. Some cultivated selections lean more towards ornamental value, while others are geared more towards rapid timber production.
Where the Kaiserbaum works particularly well
- Specimen tree on a lawn: a single focal point with plenty of distance from the house
- Shade by the patio: a fast-growing “green parasol”
- Lightly planted driveway: set further back as a loose row of trees
For an avenue effect, leave at least six metres between two trees. That way, the crowns can develop freely while still reading as a line. Each spring, the tree benefits from roughly ten litres of compost, worked in shallowly around the base.
More than ornament: timber, climate impact, and plant pairings
In Asia, Paulownia has long been grown as a timber tree. The wood is light yet stable and dries quickly. It’s used, for example, for furniture, instruments, or lightweight constructions. For most private gardeners in Central Europe, the decorative aspect comes first; still, the tree also features in climate discussions because it builds biomass rapidly.
It becomes particularly interesting when paired with other plants. Beneath the canopy, shade-tolerant perennials such as hostas, ferns, or barrenwort (Epimedium) do well. If you want to extend the insect value, add nectar-rich plants around the trunk - for instance sage, catmint, or globe thistles - which flower later in the year.
One more practical point to consider before planting: those huge leaves drop in substantial quantities in autumn. If you prefer a perfectly “tidy” garden, that can be irritating. If, on the other hand, you value leaf litter as mulch and a soil improver, you gain a free supply of material.
Overall, Paulownia suits anyone who wants quick results and is willing to give the tree some care and space in the early years. If you can offer both, you’ll be rewarded with a striking spring display, dense shade in summer, and a lively haven for insects in your own garden.
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