The room ash spreads evergreen comfort in living rooms. Integrated into the design of work spaces, the elegant ornamental plant grounds mentally minded office workers, helps reduce stress and filters the air they breathe. Its multi-faceted advantages and its lush green appearance, paired with an uncomplicated disposition, make the Radermachera sinica a perfect houseplant for beginners and advanced users. These care instructions explain in detail how you can cherish the Asian trumpet tree for many years to come. Read here where your green roommate feels comfortable, how it should be watered and fertilized. Important aspects of professional cultivation, such as cutting, repotting and wintering, receive special attention in this green guide.


  • Trumpet tree family (Bignoniaceae)
  • Genus Zimmeresche (Radermachera sinica)
  • Native to southwest China, Vietnam and Taiwan
  • Habitats mainly on mountain forest slopes up to 800 m
  • Evergreen, richly branched tree
  • Height in indoor culture 2-5 m, in the wild up to 10 m
  • Shiny green pinnate leaves on a main axis up to 30 cm long
  • Creamy white bell flowers rarely thrive in indoor culture
  • Minimum temperature: 10 degrees Celsius

Care instructions

The carpenter ash is the best-known species within the Radermachera genus, named after the officer and naturalist Jakob Cornelius Radermacher. The 15 other deciduous tree species have so far not been able to establish themselves as indoor plants in Central Europe.


The Zimmeresche favors a shady location. Specifically, this means that the green plant feels comfortable in bright light conditions as long as strong summer sun cannot reach the foliage at noon. If there is still a space on the south window sill, we recommend a distance of 50 cm from the window pane and a curtain to soften the sun. The tree is comfortable with normal room temperatures, so that no special precautions need to be taken in this regard in living rooms and offices. A cool winter at 12-16 degrees Celsius has a beneficial effect on the lifespan.

Tip : From May to September, the room ash likes to put itself in the limelight on the balcony. As long as the plant can gradually get used to the sunlight, it will happily take a sunny to partially shaded location here.


The room ash proves its undemanding frugality when it comes to choosing the right substrate. The evergreen ornamental plant thrives in commercially available compost-based potted plant soil. Add some expanded clay or lava granules to optimize permeability.


A Radermachera sinica likes a constantly slightly moist substrate. Ball dryness brings the plant out of the concept as well as waterlogging. The green plant usually reacts to such extreme loads by shedding its leaves. Experienced hobby gardeners therefore advocate not watering the room ash, but dipping it. That is how it goes:

  • If the surface of the earth dries up, the root ball is immersed in a bucket with lime-free water
  • Leave to stand in the water until no more air bubbles rise

Do not put the culture pot back in the planter until the water has completely drained off. If at all, please use a flat coaster filled with expanded clay balls or grit so that waterlogging cannot develop from here.

Tip : A high level of humidity is entirely to the taste of a room ash. Since this requirement is not always met in living rooms and offices, spray the green plant every 2 days with filtered rainwater or decalcified tap water.


The nutritional requirements of a room ash are low to moderate. If you add a liquid fertilizer for green plants to the irrigation or immersion water every 4 weeks from April to September, this list item is covered in the maintenance program. Since the plant almost ceases to grow during the low-light winter time, there is no fertilization from October to March, especially in the cool winter quarters. With year-round cultivation at normal room temperatures, you can fertilize every 8 weeks in winter in half the concentration.


If the room ash spent the summer on the balcony or terrace, when the temperature drops, the hour of moving behind glass strikes. If the mercury column sinks below 10 degrees Celsius even at night, give the plant away. The following two options are available for winter storage:

  • At the bright window seat at normal room temperatures
  • Alternatively light and cool, at 10 to 15 degrees Celsius
  • The less light is available, the cooler it should be in the room

Please set the diving intervals to the selected type of wintering. A finger test every 2 to 3 days gives precise information about whether the plant is being watered or not. Only when the substrate has dried 2 to 3 cm deep is the next water bath on the maintenance program. In the middle of the cold season, this can only be necessary every 2 weeks.


If the framework conditions are perfect, the growth of a room ash progresses rapidly. You should therefore check every 2 to 3 years whether the pot is completely rooted. If the first root strands are already growing out of the opening in the ground, repotting is an item on the maintenance plan. How to do it right:

  • An appointment at the end of winter, before the new shoot begins, is ideal
  • Spread out a drainage made of expanded clay or chippings in the new bucket over the water drain
  • Fill in a first layer of the substrate on top
  • Pot the ash tree and shake off or rinse off the used earth
  • Plant the root ball in the middle so that the previous planting depth is maintained

While you are filling in the fresh substrate, press it down a little with a wooden spoon so that no cavities are formed. Since the fresh potting soil has not yet settled, please water after repotting and immerse the root ball at a later point in time.

To cut

If the carpenter ash grows over your head or developed poor shoots in winter due to a lack of light, cut the plant back in spring. The plant is tolerant of pruning, so it is up to you to decide how much you cut the branches. However, limit the pruning measures to the herbaceous parts of the plant, as an older Radermachera sinica will sprout weaker from its woody branches. You encourage bushy growth on young plants by relaxing the shoots from time to time.


As a room ash only rarely flowers in the Central European climate, no seeds are available for propagation by sowing. They are rarely found on sale in specialist shops. This fact is not a headache anyway, as the green plant can be propagated with cuttings. This vegetative form of offspring also scores with the advantage that the resulting young plants thrive as an exact copy of their mother plant. Proceed properly in these steps:

  • In spring, in connection with pruning, cut head cuttings with a length of 10-15 cm
  • Defoliate a cutting except for the upper pair of leaves
  • Fill the growing pots with pricking soil, herb soil or a peat-sand mixture
  • Insert two-thirds of the cuttings at a time and water from below

Stick 2-3 more wooden sticks into the substrate to pull a clear plastic bag over each pot. In this way, you generate a warm, humid microclimate that promotes rooting. In the partially shaded, warm window seat, keep the potting soil slightly moist and ventilate the hood daily. The offshoots do not receive fertilizer in this phase. If new leaflets are sprouting, the cover has done its job and can be removed. When a young room ash has completely rooted its nursery pot, repot the plant and take up normal care.


Wintering that is too warm calls for spider mites, especially in connection with dry heating air. The infestation can be recognized by small speckles on the leaves and white webs in the leaf axils. In the early stages of infestation, shower the infected room ash repeatedly and spray it regularly with lime-free water. If you are dealing with a die-hard pest colony, simply cut off the pests. For this purpose, pack the Radermachera sinica airtight in a plastic bag for a few days. Before doing this, immerse the root ball extensively so that it does not dry out during this phase. This method must be repeated several times with short interruptions under high infestation pressure until no more spider mites appear.


As a year-round ornamental plant, the room ash impresses in the design of living rooms and offices. A bright, not full sun location with normal room temperatures is ideal. If you regularly submerge the plant in soft water and liquid fertilize it monthly, it will meet all expectations. Thanks to their cut tolerance, it is up to you to decide whether the pretty tree stretches up to the ceiling or remains at the height of the potted flowers. The plant can easily tolerate pruning in early spring. Every 2 to 3 years, the neat green plant appreciates the change to a larger container with fresh soil. A cool overwintering at 10 to 15 degrees Celsius contributes to a long lifespan and keeps spider mites at bay.

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