Houseplant of the month

Radermachera sinica: The July 2023 Houseplant of the Month

Photo by Diego Alex.

The other day, as often happens, I brought home a new plant and showed it to my boyfriend. Usually, his response is vaguely interested at best, “That’s cute” and, two seconds later, he couldn’t say anything about the plant except that it’s green. However, I had a different response when I brought home a small pot of Radermachera sinica seedlings: “It looks like parsley”.

Any plant that draws a divergent response deserves to be plant of the month!

Apparently, it looks like parsley. Photo by the author.

Origin

Belonging to the Bignoniaceae family, Radermachera is a genus of 17 tree species from Southeast Asia. It was named after the Dutch botanist Jacob Cornelis Matthieu Radermacher, who worked extensively on the flora and fauna of Indonesia. He was tragically killed in a mutiny aboard his ship on December 24, 1783, when he was in his early forties.

Of all the Radermachera species that exist, only R. sinica is cultivated as a houseplant, an interest that is actually rather recent. There is as yet no cultivar other than its basic form. Its common names are Radermacher de Chine and, in English, China Doll, Asian Bell Tree, Emerald Tree or Serpent Tree.

Description

Radermachera are deciduous trees with bipinnate or tripinnate leaves, i.e. each leaf is composed of a common petiole and, laterally, secondary petioles from which emerge the leaflets, toothed or not. The leaflets, which may or may not be toothed, are shiny green and are the plant’s main attraction. In the wild, Radermachera is a tree with a thick trunk, up to a metre in diameter and reaching heights of up to 30 metres, and an astronomical number of small leaflets 2 to 4 centimetres long. The trumpet-shaped, white flowers bloom at night and die at dawn.

In countries where temperatures don’t drop below 5 degrees Celsius, Radermachera sinica is a beautiful tree with dense foliage. Photo by Forest & Kim Starr.

The radermachera looks very different as a houseplant. First of all, although it grows quite rapidly, it will rarely exceed 1.5 meters in height. Its upright stem, green at first, covers itself with bark as it ages and remains narrow throughout its life. If pruned, radermachera can produce more branches and a less wiry appearance. Several seedlings or juvenile plants are often sold in the same pot to give it a bushy appearance. It does not flower indoors.

This is radermachera sinica at its bushiest. Unless it receives exceptional care, it tends to become a little balder in our indoor conditions.Photo par NicoNico.

Growing Tips

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Light

Admittedly, radermachera is said to tolerate medium to low light, and it will… for a while. However, it will only grow well in the sun. It’s a good idea to let it spend the summer outdoors – it will then gradually become accustomed to full sun. 

Yes, the plant will survive direct sunlight. That’s the light in which it thrives outdoors! Photo by Forest & Kim Starr.

Watering

Probably the most difficult aspect of growing radermachera is understanding its watering needs. In fact, this is why many people have trouble keeping it for long. You have to be very careful, because optimal watering is difficult to achieve: you want even, constantly moist soil, but you don’t want the roots to drag in the water. If radermachera receives too much water, its leaves turn black, and if it doesn’t get enough, they turn yellow as they dry out.

Pay close attention to your plant’s behavior to adjust.

Atmospheric Humidity

In a dry environment, radermachera’s basal leaves dry out quickly (especially if not watered). It needs slightly higher humidity than many plants commonly grown indoors. On the other hand, it’s not too demanding either: I have mine surrounded by a dozen other plants, creating a slightly more humid microclimate, and it’s doing quite well. Otherwise, you can always put a humidifier nearby, especially during the winter months, to increase humidity.

Like most thin-leafed plants, radermachera requires higher atmospheric humidity than is usually found in homes. Photo by David J. Stang.

Potting soil and potting

A potting soil for houseplants will do just fine, especially one made from coconut fibers, which are easier to keep evenly moist.

Fertilizers

Recommended dose during the growing season.

Temperature

A temperature between 6 and 24 degrees Celsius is recommended. Avoid intense heat (over 25 degrees). See below for my own experience with this recommendation.

Care

Under the right conditions, radermachera has a vigorous growth habit and needs to be pruned to prevent it skyrocketing. Pruning stimulates branching, enabling the plant to become more compact and generally more attractive. Occasionally, the dried basal leaves should be removed (they detach easily). Finally, it’s a good idea to take it outside during the summer and bring it inside as soon as temperatures drop below 15?

Multiplication

It can be propagated by taking cuttings from stems not yet covered in bark, or by marcotting, for those who like to make things difficult for themselves. It’s also apparently possible to grow it from seed, but again, I’d settle for the traditional cutting.

Problems

  • Yellowing base leaflets: lack of water, low atmospheric humidity;
  • Leaflets with blackened tips: excess water;
  • Pests: whiteflies, mealybugs, aphids, spider mites and thrips.

Toxicity

Non-toxic, but the sap may irritate those sensitive to it.

Tips on Purchasing

Radermacheras are often sold as a cluster of seedlings. Although attractive, seedlings are not particularly happy in this environment. What to do when your houseplant is a clump of seedlings?

Now for My Story

I bought a small radermachera which, according to some people, vaguely resembles parsley. I placed it a metre from a south-facing window, with good light. One by one, the seedlings that made up the beautiful pot began to dry out and die, although I kept the potting soil evenly moist (to the best of my ability). It seemed hopeless.

There was only one plant left at the end of that fateful spring and, in my terrible dismay, I decided to give it my best shot: I took the unfortunate plant, repotted it in a modest-sized flower box and tossed it, without much delicacy, into a spot outside, in full sun, for the whole summer.

A few weeks later, as I watered it occasionally, but not that much, I was surprised to see the radermachera not only pick up again, but also sprout leaflets, develop a small trunk strong enough to withstand summer gusts and, above all, fill out with multiple new stems, giving it a very pretty appearance.

What a Surprise, What a Treat!

Of course, with all the trouble it had given me, I was dreading the return to school, when I had to repot it again, squeezing the mass of roots it had made in the meantime, and put it back in its place in a pot that was too small, a little too far from a window and with typical indoor humidity, but with too many plants (another of my boyfriend’s observations).

Que nenni! Since then, this plant has been very easy to care for, provided I pay a little attention to watering (I forgot once and it lost a few leaves, that’s all). No other quirks, no other problems, no insects, just happiness.

Perhaps my experience is unique. However, here’s my advice if you want to try your hand at growing Radermachera sinica: don’t cry too much if two or three plants go to pot… and buy it in spring or early summer!

My little plant, after its summer outside, in great shape! Photo by the author.

The radermachera sinica is a rising star among houseplants, despite a delicate culture, especially sensitive to light and humidity. However, once you get used to it – and it gets used to you – it’s a pretty plant, thanks to the shape of its leaves and their beautiful, glossy green color.

And here it is, after a first winter indoors, ready to be taken out for the summer… Granted, it’s not as dense as those sold in stores, but its wiry appearance is also part of its charm!

Colin Laverdure has no qualifications other than his last name (Laverdure is French for "the greenery") and a slightly excessive passion for plants of all kinds, but particularly for houseplants. When he's not watering his personal collection, he's interested in writing fiction or singing with his choir.

2 comments on “Radermachera sinica: The July 2023 Houseplant of the Month

  1. Ferne Dalton

    For anyone else wondering, marcotting=air layering.

  2. Gisela Huelsman

    You love your plants it shows keep up the good work!

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