Gentian tree, potato tree, blue nightshade or Solanum rantonnetii – the gentian bush has many names. But whatever it is called, the gentian tree is a flowery eye-catcher. To keep it that way, however, he needs a lot of care and attention. Because only when its high standards are met, it will thrive and regularly produce its bright flowers.

Find the right location for the gentian tree

Solanum rantonnetii – whether grown as a gentian tree or a gentian bush – needs plenty of sun. Since his home is in warm South America, he cannot tolerate cold winds either. And frost can quickly kill him.

So the location for the potato tree should meet the following conditions:

  • Very bright, preferably in direct sunlight
  • Protected from wind and weather
  • Warm
  • Moderately dry

The area near a wall or in a corner of a house is ideal. As long as they don’t cast too much shade on the plant.

In addition, it must be ensured that the gentian tree can reach a height of four meters. At least if it is planted freely in the garden. Sufficient space upwards is therefore also required.

Due to its love for warmth and sun and its initially small size, the gentian tree can also be cultivated in a tub and placed on south-facing balconies.

Bucket or free in the garden?
In order to get a spreading, large plant, it is preferable to plant it freely in the garden. But it also has a major disadvantage. Since the potato tree does not tolerate frost, it would have to be dug up every year at temperatures below seven degrees and brought inside. In a bucket, this is much easier and can be done without a lot of effort.


As high as the demands on the location are, the gentian bush is also picky about the substrate. The soil must be rich in nutrients, low in lime and humus. In addition, it should be able to hold moisture well without being prone to waterlogging or compaction.

It is beneficial to use normal garden soil or bucket soil. This should be of high quality, fresh and pre-fertilized. So that it also otherwise meets the needs of the Solanum rantonnetii, a good portion of rotted compost can also be mixed in with it. A combination with coconut fibers also works extremely well for the gentian tree.

Culture in the bucket

As already mentioned, the cultivation of the gentian bush in the bucket is possible and even preferable. The small space for the roots and regular pruning keep the plant small without harm.

Again, all you need is a protected but very warm and sunny location and the right substrate. A south-facing balcony or a bright terrace are ideal.

Bucket soil with compost and coconut fibers is the optimal basis. In addition, the container should be chosen as large as possible. Because even in the bucket culture, the Solanum rantonnetii can reach a height of two meters.


Due to its preference for warmth and sun, the gentian tree should only be planted when temperature drops or even frost are no longer to be expected. Late spring or early summer is ideal.

This point in time does not necessarily have to be waited for in the bucket. Planted in spring, the container can simply be moved inside as soon as the temperature drops.

Apart from this, the planting hole must be prepared with the appropriate substrate. After the planting, the earth should be pounded and the gentian tree should be watered. It doesn’t matter whether Solanum rantonnetii ends up in the bucket or free in the garden.


The potato tree needs a lot of care, which must be done regularly and closely. This plant is completely unsuitable for anyone who wants to make little effort with a balcony or garden.

Correct watering is part of maintenance and the right time has to be chosen. Furthermore, a frequent supply of nutrients in the form of a suitable fertilizer is necessary.

If the gentian tree is to retain its shape as a tall trunk, it must also be continuously but carefully cut.


There are a few things to consider when pouring. So the water must neither be too cold nor too hard. Ideal are:

  • Rainwater
  • Untreated pond water
  • Stale or filtered tap water

Fresh tap water can also be used if it is very soft – i.e. contains little lime. This information can be obtained from the local waterworks or it can be determined using inexpensive test strips.

And of course the water shouldn’t be too cold. Room temperature is generally ideal.

However, watering the Solanums rantonnetii requires more than just the right water and a mild temperature. It also needs to be done at the appropriate time. The roots should always find a slightly moist substrate, but never dry out completely or stand too wet in return. As a guide, the top layer of the earth should occasionally dry out a little. Furthermore, only a little watering is allowed after planting. So it is better to water very little twice a week than to wash once every two weeks.

In summer and when cultivating in the bucket, more frequent watering is necessary. The cooler it gets, the less often you have to use the watering can.


The gentian bush or tree needs a large amount of nutrients. This need is actually so great that even the pre-fertilized substrate does not last long.

For this reason, it is necessary to fertilize at least once a week from spring to autumn – i.e. throughout the entire flowering phase, or even better, twice a week.

Liquid complete fertilizers are suitable for flowering plants or potted plants or blue grain. A weak concentration is recommended.

Caution: If the potato tree loses leaves in the lower area, this is a sure sign of an existing nutrient deficiency. If this occurs, only a slightly diluted fertilizer should be used.

With falling temperatures in autumn, the additional supply of nutrients can slowly be tapered off.

To cut

So that the gentian tree retains its shape, grows densely but still bears a rich bloom, regularity and caution must be exercised when cutting.

The ideal time for the correction is spring, before the potato tree sprouts again. In any case, only gently and without sacrificing a lot of length. For this purpose, it is also advisable to use scissors throughout the year if necessary and to correct even small deviations.

If a shoot – whether it has numerous buds and flowers or not – clearly shoots out of the desired shape, it should be cut early. The time in the year does not matter. In this way the Solanum rantonnetii can save its strength for a denser growth, new flowers and growth.

If the shoots are left to grow uncontrollably or if they are too late and then radically shortened, the bloom does not benefit. As a rule, many green leaves then grow or the roots receive an impulse to sprout, but the characteristic blue flowers do not appear. The main pruning should still be done in spring and not just before the first frost in autumn.

Moving and repotting

Fresh, high-quality soil is generally good for Solanum rantonnetii. However, transplanting is not always necessary here. Instead, the new substrate can simply be worked under.

While the gentian tree should remain free in the garden in the same location as possible, or should be placed there again and again after wintering, i.e. repositioning is only advisable if it is not thriving or there is not enough space, the culture in the bucket shows a different picture.

Here the blue nightshade has significantly less space to spread its roots in search of nutrients. In addition, the substrate will quickly be depleted and used up through frequent watering and high consumption of nutrients. Even if fertilizers are applied regularly. Repotting is therefore necessary once a year. And, like the blending, should be done in spring.

However, a larger bucket does not have to be provided every year. A slight increase every second or third year is sufficient. Instead, the old substrate simply has to be thoroughly removed and replaced with new soil. This is followed by plenty of watering for the next two to three weeks.


The gentian tree can be propagated quite easily using cuttings, but it is not always successful.

The following steps are necessary for this:

  1. Obtain cuttings from June to July by cutting off heads that are 10 to 15 cm long.
  2. The resulting cuttings are placed in moist potting soil and covered with foil.
  3. Using root aid can help.
  4. Propagation is successful when the first new shoots appear on the cuttings.
  5. When the young plants have reached a height of 20 cm, the foil can be removed and the small potato trees can be taken outside in warm weather.
  6. From a height of 30 cm, if the growth habit is desired as a high trunk, the shaping cut can be started slowly and carefully.


The gentian tree is generally not hardy and accordingly does not tolerate frost. This is not a problem in the tub. If the outside temperature drops to around 10 ° C, the plant is simply moved to a room with the same temperature. This should be bright and well ventilated. In addition, the temperature must not drop below 7 ° C. Careful watering is still necessary, but fertilizing is not.

This is easy to do in the bucket. It is even possible to spend the winter in a warmer place in the apartment. However, if the Solanum rantonnetii was planted freely in the garden, the plant must be dug up every year and placed in a container. In the long run this is very cumbersome and time-consuming. In the mild wine-growing climate, excavation is not absolutely necessary. The gentian tree should still be protected comprehensively with garden fleece, straw and brushwood.

Tip: Some sources still recommend wintering Solanum rantonnetii in a dark and cooler place. This procedure ensures, on the one hand, that the plant loses all leaves and, on the other hand, delays the flowering phase considerably.

Typical diseases and pests

The gentian bush is not susceptible to diseases, but it can be attacked by pests. White flies, spider mites and aphids are the typical parasites that are found on the plant, especially during hibernation.
With regular checks and immediate use of home remedies, such as nettle liquid manure and a solution of water and solid soft soap, an infestation can be quickly identified and eliminated.

Is the gentian tree poisonous?
As a nightshade plant, the gentian bush is highly poisonous in all its parts. For humans and animals. Skin contact or licking off the sap is sufficient for this. For this reason, gloves should be worn during the cut. Solanum rantonnetii is also not suitable for gardens, balconies or terraces in or on which children or animals play.

The gentian bush is a plant that requires a lot of care and needs attention all year round. And that means a lot of effort. Although it rewards it with abundant flowering, the gentian tree is still not suitable for those who prefer to relax in the garden rather than painting.

Similar Posts

Leave a Reply

Your email address will not be published. Required fields are marked *