Bubble ash, Koelreuteria paniculata – care tips

The bladder ash trees have nothing to do with our native ash trees, the two “ash trees” split up far above the order in the plant kingdom. Bladder ash belongs to the soap tree family (mint family ash, olive family). The family of the lantern trees is called the soap tree family, the genus Koelreuteria, and is native to East Asia. The Koelreuteria include only three species, all of which form capsule fruits. So protect your precious seeds (only three per capsule) with a bubble-shaped shell during maturity.

The pericarps of the bladder trees are reminiscent of the pericarps of the bladder cherries (physalis), which include the cape gooseberry (physalis, for eating) and the lantern flowers (physalis alkekengi). They also turn similarly decorative from pink to reddish-brown as they mature (September, October), hence the name of the beautiful tree, Bubble Tree and Lantern Tree; the “bubble ash” comes from the resemblance of the pinnate leaves to ash leaves.

These bladder ash trees are deciduous and attractively pinnate, the fresh leaf shoots (mid-May) are attractively reddish; the yellow flowers appear in large inflorescences of up to 40 cm in diameter in July/August and are really pretty to look at, as is the orange autumn color of the foliage.

location

So all in all a very ornamental tree that deserves a location on a visual axis where it will be visible throughout the long season.

How much space you need to reserve for the pretty shrub depends on how you shape the growth of the bubble tree. The bladder ash can be cultivated as a tree or stately shrub, reaching heights of growth of up to 15 meters and a trunk diameter of up to 50 cm as a standard. As a tree, the bubble tree needs enough space at the top and up to a good 5 meters of space for the flat, umbrella-shaped crown (except for K. paniculata ‘Fastigiata’, see varieties below). The shrub needs similar space for lateral spread.

If you plant the bubble tree at some distance from the garden seat, it will distract many annoying insects. It is regarded as an ecologically valuable nutrient for bees, and what bees like, other useful and rare insects as well as butterflies also like.

The bladder ash does not otherwise have great demands on the location, likes a lot of sun and a permeable soil that can be dry to moist, the bladder ash likes to adapt to it. Nutrients do not have to be available in abundance either, in China the lantern tree grows on flat, fairly poor soil.

Koelreuteria paniculata should even tolerate a location on a busy street without shade. The bladder ash can also withstand wind, but not if it constantly brings fine seawater with it. Don’t worry about cables in the ground, the strong, fleshy main root spreads flat and only branches out a little.

Bubble ash in bucket

The bladder ash can be kept in a bucket, but it should then be a large bucket. The planter can be left outside all year round with good winter protection. Especially in the first few years, it is advisable to overwinter the quite frost-sensitive young plant indoors, in a cool room.

You can also keep the bladder ash indoors all the time, preferably in a beautifully light-flooded conservatory that is hardly heated in winter.

Bare root, root ball, container

Whether or not your bladder ash develops the above-mentioned strong and fleshy main root depends on how the plant was raised and what root it is sold with.

Shrubs are sold bare root, with a root ball grown outdoors, or grown in containers. There are significant differences between these forms:

1. Shrub with soil ball

These trees can grow in the nursery just as they do in nature. In many cases, the best choice for hobby gardeners, so you don’t have to worry about pruning or the disadvantages that container plants often have. The tree with root ball has these advantages:

• Outdoor rearing increases resilience.
• Especially with frost-sensitive plants that are grown in the local region.
• The growth of trees raised outside is usually stronger and bushier.
• The root system can develop properly in outdoor plants.
• Cutting off roots when digging up leads to fine root formation after planting.
• This creates very vital roots that grow directly into the new soil.
• This means that a ball plant grows better than a container plant.
• Outdoor plants are potted with clods of soil and not with artificially assembled substrate.
• That also helps with growth.
• In addition, the water supply works better because such plants have better capillarity.

Transplanting an outdoor plant into your garden causes “planting stress”, which expert tree nurseries prevent by so-called “straining” (transplanting). Such nurseries can tell you exactly how often an outdoor plant has already been schooled when you buy it.

The only perceived disadvantage of an outdoor plant with a ball of soil – that it can only be transplanted during the natural dormant season – is in fact none: there is little reason to plant woody plants “always”, for all plant physiology fall is the best planting time.

2. Bare roots

is usually planted in forestry and fruit growing, where not one, but around 1,000 trees have to be planted at once. Trees with bare roots have also been grown outdoors in the tree nursery, right up to strong young plants. They are “harvested”, sold and planted during the dormant phase. Harvesting means that only the root itself is carefully pulled out of the soil at planting time (early spring, late autumn when the plant has/not yet had leaves) with no soil around the roots and is sold without a pot. Since this saves work (digging out, transporting heavy bales) and material (soil, pots), bare-rooted trees and shrubs are offered very cheaply. However, they need a plant pruning (cut shoots by 1/3) and root pruning (remove damaged root parts, cut back strong roots,

Quite interesting for hobby gardeners, little can happen, these plants cost “cents”. If you can buy a bare-rooted bladder ash in autumn, you can definitely access it, if you ask, the planting will usually be cut for you in the nursery. You will probably pay a tenth the price of a container plant, however, the planting pit in the garden should already be prepared.

3. Containerpflanzen

Container plants are offered in bulk, especially for private gardeners, although the cultivation of plants in containers has some disadvantages:

• Root development very often leaves a lot to be desired.
• Especially when growing in closed plastic pots, the roots are concentrated at the edge of the pot.
• There a matted root system develops, inside a lonely and thin main root.
• The root system often grows in circles, which is not good for later development
• The whole grove is weaker than the colleague grown in the field.
• The container plant grows in a substrate that is not necessarily similar to garden soil.
• This causes considerable stress when getting used to “the normal environment”.

There are also carefully grown container plants whose root growth is carefully observed in open/perforated containers. When in doubt, you will notice this in the higher price, but with a plant that is usually not exactly cheap, such as the bladder ash, you should definitely inquire how the container plant was grown – high prices can also be taken without care. If the retailer cannot give you any information about this, doubts are appropriate.

Doubt should generally lead away from the container: if more gardeners were to choose plants that were allowed to develop proper roots, it would also save vast amounts of peat and plastic, so it would be a win for the gardens and for the environment.

plant

The bladder ash with root balls can be planted in autumn or, if necessary, in spring. Planting is simple:

• Dig a hole so that the bubble ash disappears into the earth up to the top edge of the earth ball
• It is better to plant a little too high than to partially plant the trunk
• Leave compostable wrappers around the globe
• Stabilize unstable trees with thin trunks with ground anchors
• These are stakes that are driven in at an angle and without touching the root
• This anchorage should be left alone for at least 2 years so that the tree can grow well
• Sie bewahrt die Feinwurzeln davor, bei jedem Wind abzureißen
• Nach dem Pflanzen angießen und ggf. Erde nachfüllen

Pflege und Schneiden

Die Pflege in der Saison beschränkt sich darauf, dem Blasenbaum in Fällen großer Trockenheit etwas Wasser zukommen zu lassen.

Düngen sollten Sie ihn auf keinen Fall. Er ist „Askese“ gewohnt und könnte auch auf einmal wie verrückt, aber nicht besonders schön zu wachsen anfangen. Dann brauchen Sie einen Baumdoktor, jeder selbst vorgenommene Schnittversuch bringt meist noch mehr Wasserschosser hervor …

Im Normalfall brauchen Sie die Blasenesche nämlich nicht schneiden. Sie darf ganz alleine ihre gefällige Kronenform entwickeln und wird Ihnen mit dem normalen Jahreszuwachs von etwa 20 cm auch nicht so schnell über den Kopf wachsen.

Überwinterung

If you have purchased a non-close grown bladder tree that the gardener has designated as hardy, your primary care efforts for the first few years will revolve around getting that bladder tree well through the winter.

Container plants usually grow up in greenhouses and are not used to the cold, so you should give such young plants good winter protection and, above all, make sure that they are not left unprotected by late frosts. This also applies to mature bladder ash trees, which are otherwise reliably hardy in Central Europe.

propagation

If you would like to have several of these decorative lantern trees in your garden, you should consider propagating them. Because the bubble ash trees are in demand, which is reflected in the high prices: A Koelreuteria paniculata that has grown in soil outdoors costs a good 200 euros as a standard with a height of around 200 cm, or almost EUR 200 if it is to be 400 cm 800 EUR.

You won’t get a much cheaper bubble tree grown in a container either. 150 cm costs around EUR 150, 300 cm already around EUR 350, multi-stemmed around EUR 600. The columnar bladder tree Koelreuteria paniculata ‘Fastigiata’ is a little more expensive, 400 cm around EUR 1,000. If you find offers of 80 cm bubble ash for a few euros, you can buy them, but you will probably be able to bury the bubble ash soon.

A propagation attempt with shoots from your own bubble tree is more worthwhile, even if bubble trees are probably not very cheap because they are not supposed to be easy to propagate. How to proceed:

• Take root cuttings of 4 cm, preferably in December
• Place in pots lying flat and set up in a warm place
• Keep moist and wait

You can also sow seeds, but that’s a separate chapter because the seeds need stratification and some special treatment.

species and varieties

The genus contains three East Asian species:

• Koelreuteria bipinnata: Known as the Chinese Flame Tree in English, while the Koelreuteria paniculata is “just” called the Golden Raintree, offers magical colors.
• Koelreuteria elegans: Hard to find here because it is not hardy here.
• Our bladder ash Koelreuteria paniculata with the cultivated forms ‘Coral Sun’ (new, splendid colors when sprouting), ‘Fastigiata’ (columnar growth) ‘September’ (late flowering, less frost hardy).

Conclusion
The bubble tree is a welcome guest with us because it looks good, is a comfortable size and ecologically “fits in” – our insects like it. If you plant a bladder ash grown here with a root ball, care is almost limited to admiration. Container plants grown here need warmth, shelter and attention for overwintering; with imported blistered ash trees in the container you don’t need any care tips at all, they will most likely die out soon anyway.