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The ball trumpet tree (Catalpa bignonioides 'Nana') is an attractive eye-catcher even in small gardens with its large, heart-shaped leaves. The ball trumpet tree, also known as the dwarf trumpet tree, grows slowly in contrast to its larger relative.

In a nutshell

  • grows slowly: only 20 to 30 centimeters / year
  • less if the conditions are less than ideal
  • water regularly when dry
  • up to seven meters high
  • up to seven meters wide

Ball trumpet tree: growth per year

Only the 'Nana' variety is referred to as the ball trumpet tree, which, in contrast to the up to 15 meter high original species Catalpa bignonioides, remains significantly smaller and also shows slower growth.

  • Growth per year: 20 to 30 centimeters under optimal conditions
  • maximum growth height: four to seven meters
  • maximum growth width: four to seven meters

If the growth conditions during the spring and summer months are not very favourable, the annual increase will be lower or even stagnate. The crown only grows spherical in the first few years, in older specimens it widens considerably. That is why older globe trumpet trees are often as wide as they are tall - this growth behavior should be considered when choosing a location. Otherwise it can happen that after a few years the trees no longer have enough space.

Source (l.): Rasbak, Catalpa bignonioides 'Nana' (02), edited by Plantopedia, CC BY-SA 3.0

Tip: To keep the ball trumpet tree small, you can also cultivate it in a bucket. Root growth is limited here, which means that shoot growth is also reduced.

Ideal growing conditions

So that the ball trumpet tree does not stagnate in its growth, it needs optimal conditions:

  • sunny to semi-sunny location
  • sheltered, warm place
  • moist and nutrient-rich soil
  • loose, permeable soil
  • no waterlogging

Specimens kept in tubs need as much space as possible for their roots and should be watered and fertilized regularly. The substrate must not dry out, even a lack of nutrients is fatal for healthy growth. So that the potting soil is moist but not wet (this promotes root rot), drainage and a drain for excess watering should not be missing.

Tip: Also in contrast to the original species, the small ball trumpet tree is somewhat more sensitive to cold, which is why winter protection should not be missing during the cold season.

Ball trumpet tree not growing

If the ball trumpet tree does not want to grow properly or even seems to have stopped growing, either the conditions are not ideal or the weather is not suitable. In hot, dry years, for example, hardly any new shoots seem to develop. Additional watering and fertilizing of planted specimens can help to stimulate growth here:

  • Keep root area constantly moist
  • fertilize with horn shavings three times a year
  • also suitable complete fertilizer for woody plants
  • first fertilization in April
  • last fertilization at the end of July
Regular fertilizing with horn shavings will help the ball trumpet tree to grow better.

With appropriate precautions, the desired shoot growth can still be achieved despite unsuitable climate. If, on the other hand, the less than ideal location is the cause, only replanting the tree will help.

Tip: Typical of Catalpa is not only the slow growth, but also the late budding of the leaves. The leaves often do not develop until mid to late May and must be protected from late frosts.

frequently asked Questions

Where does the ball trumpet tree originally come from?

The trumpet tree (Catalpa bignonioides) is native to the south-east of the USA, where the trees, which are up to 15 meters high, grow along rivers in moist soil rich in humus and minerals. The ball trumpet tree, on the other hand, is a significantly smaller variety of the original species due to breeding and grafting, but which produces neither flowers nor fruit.

Can I keep the ball trumpet tree small by pruning?

In principle, the ball trumpet tree can be cut back and will sprout again even with severe pruning, provided that this is done above the grafting point. However, it is not a good idea to try to keep trees small by pruning - pruning always leads to stronger growth. In particular, the branches should not be shortened, as they will then sprout again like a broom and thus impair the natural, harmonious appearance of the tree. It is therefore advisable to select trees that match the available space.

Is the ball trumpet tree poisonous?

If you rub the delicate green leaves of the trumpet tree between your fingers, they give off a strong smell. The scent is due to a species-specific mixture of catalpin, catalposide, and other related chemicals. They are considered to be only slightly poisonous and are therefore harmless to humans and animals. However, the strong smell keeps mosquitoes away, so that the dwarf trumpet tree can serve as a natural mosquito repellent.

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Garden plants