Blue potato bush: planting, care & overwintering

The blue potato bush with its blue-violet flowers is a real jewel for balconies and patios.

The blue potato bush (Lycianthes rantonnetii), also known as the blue potato vine or potato tree plant, attracts all eyes with its ceaseless flowering. It is a particularly decorative ornamental shrub when grown as a standard tree. All information about the blue potato bush, planting and its demanding care can be found here.

Blue potato bush: Origin and characteristics

The decorative blue potato bush is a woody plant and owes its name to the numerous blue flowers. It is also known as the potato bush or potato flower because the flowers are shaped similarly to those of the potato plant. Originally, the plant comes from the subtropical region from Argentina to Paraguay. Botanically speaking, the blue potato bush, just like the potato, belongs to the nightshade family (Solanaceae). From May to October, the blue potato vine produces numerous blue or white, star-shaped flowers with a conspicuous yellow stamen in the centre. They stand together in groups of 2 to 5 blue potato bush flowers. The lush flowering can be enhanced by regular pruning. The green leaves are ovate, pointed and alternate on the slender branches. The fruits of the blue potato bush are red berries about 2cm in size, which resemble tomatoes. These are readily eaten by birds, spreading the seeds at the same time. The potato bush has an upright growth, reaches a height of up to 2 m and is not hardy. That’s why we cultivate it as a tub plant and so it can be easily overwintered. The blue potato bush is usually available as a standard tree.

Is the blue potato bush bee-friendly? Yes, the blue potato bush is bee-friendly. For bees and other insects it offers a lot of nectar as a food source. Due to its extremely long flowering period, it reliably supplies insects from March to October.

The most beautiful varieties

• ‘Variegata’: the blue potato bush ‘Variegata’ has blue flowers and features white-green variegated foliage.
• ‘Alba’: the shrub ‘Alba’ captivates with its white flowers. Individual blue potato bush flowers exhibit light blue-violet stripes here.

• ‘Royal Robe’: the blue potato bush ‘Royal Robe’ has numerous bright purple flowers.

Planting blue potato bush

For your blue potato bush to flower magnificently, the right location is of great importance. This should be warm, full sun and protected from the wind. The more sun the shrub gets, the more luxuriantly it will flower. To protect the blue potato bush from wind and rain, it should be placed against a wall, a fence or under a canopy. Good locations are, for example, a terrace or balcony with a southern exposure.

Blue potato vines like nutrient-rich, loose, well-drained and humus-rich soil. They prefer to grow on lighter soils, but can also cope with heavier substrates with sufficient drainage in the subsoil. The pH value should be in the neutral to slightly alkaline range — i.e. between 6 and 7.8. For example, our Plantura Organic Enriched Compost is recommended here. It is ideal for all plants with high nutrient and lime requirements and supports healthy root growth. The peat-free soil with its high humus content ensures active soil life and correspondingly good soil fertility.

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The plants that are available in containers in garden shops are usually already 1 to 2 years old and need to be repotted into a larger container. This is how you plant a blue potato bush:

• The optimal time for planting is in spring after the Ice Saints, i.e. from mid-May.
• You need a sufficiently large container with water drainage so that the root ball has plenty of space and water can run off.
• Remove the blue potato bush from the previous planter and soak the root ball in a bucket of rainwater.
• It is essential to place some clay shards as a drainage layer over the water drainage to avoid waterlogging.
• Then fill the planter with the substrate described above. Place the blue potato bush in the centre of the container and fill the gaps with compost.
• The substrate is pressed down and a watering margin of 2 to 3cm is left free.
• Finally, the blue potato bush must be watered well.

Tip: As the blue potato bush can become quite large and heavy, it is helpful to place the tub on a mobile base. In this way, the potato bush can be rolled to the appropriate location as needed.

Caring for Lycianthes rantonnetii

The blue potato bush requires daily attention before it bears magnificent flowers. This ornamental shrub, which is not so easy to care for, requires a sure instinct for watering, fertilising, pruning and overwintering. However, given the right location and care, this decorative plant will reward you with its long-lasting, violet-blue sea of flowers.

Watering and fertilising

The blue potato bush has a high water requirement. The trick is to keep the soil evenly moist. To do this, it is best to check the substrate with your fingers in the morning and evening. The soil must never be allowed to dry out completely, but the ornamental shrub does not tolerate waterlogging either. On very hot days, watering must be done daily in any case, sometimes even twice a day – in the morning and in the evening. In general, do not water too much at once, but more frequently instead. As the plant tolerates only a small amount of lime, rainwater or decalcified, stale tap water is best suited for watering.

In order for the blue potato bush to flower tirelessly, regular fertilisation is necessary in addition to sufficient sun. Add a portion of organic liquid fertiliser to the water once a week between March and September. For this purpose our Plantura Liquid Flower Food is recommended. Our organic liquid fertiliser can be applied quickly and easily with the water, which makes fertilising very easy, especially for large potted plants.

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Pruning the blue potato bush

Proper pruning is also an important part of caring for Lycianthes rantonnetii. How to prune the blue potato bush correctly:

• Ideally, pruning should be done in the spring before new shoots.
• When pruning, the shoots are shortened to a maximum of one third.
• Pruning should only take place in autumn if the blue potato bush will otherwise no longer fit into the winter quarters.
• During flowering, the blue potato vine can always be easily kept in shape by pruning excessively long shoots that grow out of the crown.
• Withered and diseased branches may always be cut out completely.
• Withered flowers should be removed regularly.

Tip: always wear gloves when pruning back your blue potato bush. The plant is slightly poisonous and symptoms of poisoning can occur even on contact with the skin.

Repotting the blue potato bush

You should repot your blue potato bush every 2 years. Even if the pot has not yet become too small, this will give the plant fresh substrate and additional nutrients that the fertiliser may not have contained. This is particularly relevant when using liquid fertilisers, which for chemical reasons cannot hold all essential nutrients in solution. The best time to repot blue potato vines is in spring shortly after pruning. If your blue potato bush is to grow even larger, it will need an ever bigger pot. Make sure to shake out the old soil from the root ball as much as possible. The shrub also tolerates root pruning to limit overall growth. When planting, proceed in the same way as described above.

Common problems

Mistakes in care such as improper pruning, lack of nutrients and water or an unsuitable location are not easily forgiven by the blue potato bush. Because these mistakes often result in pest infestation and plant diseases:

• The blue potato bush is readily attacked by leaf lice (Aphidoidea). This in turn often triggers an infestation of sooty mould, which turns the leaves black – this does not damage the blue potato bush directly, but it does prevent it from photosynthesising.
• Spider mites (Tetranychidae) are also often found on the potato bush. These can be recognised by their silvery speckled leaves.
• Infestation with whitefly (Aleyrodes proletella) is when small, white insects fly up when the plant is touched or shaken.

The best way to prevent this is through the right care measures and the right location. If an infestation nevertheless occurs, the shrub can be sprayed several times with field horsetail tea. Spraying with a powerful jet of water is not recommended, as the delicate blue potato bush leaves and flowers could be damaged by the water jet. Neem-containing organic sprays are also approved against many piercing-sucking pests on the blue potato bush.

Tip: pests can quickly become a nuisance, especially in warm winter quarters. In our special articles you will find numerous control methods against various pests.

Blue potato bush loses leaves: yellow leaves and leaf drop are an indication of nutrient deficiency. Make sure you fertilise regularly between March and September, about once a week, and ideally use rainwater for watering.

Why won’t my blue potato bush blossom? If the flowering of the blue potato bush fails, it may be due to various reasons. Either the overwintering was too warm – or too cold and too dark. In this case, a more suitable winter quarters should be found next winter. Nutrient deficiency or drought stress also causes flowering to fail. To remedy the problem, fertilisation and water supply must be adjusted. An unsuitable location can also be a cause for a lack of flowering. Make sure the plant is in full sun and in a place sheltered from the wind. Also avoid pruning too much so that the blue potato bush does not fail to flower.

Tip: to stimulate the blue potato bush to flower, the shoots can be pruned.
To do this, continuously cut off the tips of the young branches. In this way, the shrub branches out more and more flower clusters are produced.

Overwintering blue potato bush

The blue potato bush is not winter-hardy and must be winter-hibernated accordingly. Pruning is advisable before the warm winter to reduce pest pressure. Bring the shrub into the winter quarters early – when temperatures drop below 7 °C, because it will freeze even at temperatures slightly below zero. The optimal location during winter is bright and moderately warm at a temperature of 8 to 12 °C. Under these conditions, the blue potato bush retains its leaves. If it is overwintered in a darker place, it will shed its foliage and probably flower a little later the next year. Fertilisation is not necessary between October and February. However, the plant must continue to be watered regularly, but only a little, so that it never dries out completely. Regular airing prevents fungal diseases. In addition, the blue potato bush tree should be checked for pests from time to time.

Is the blue potato bush poisonous?

Yes, the blue potato bush is poisonous. Like all plants of the nightshade family, it contains toxins in all parts of the plant. Fruits, flowers and leaves should not be put in the mouth under any circumstances, because eating even small amounts causes vomiting, malaise, weakness and stomach cramps. Larger doses lead to respiratory paralysis, circulatory collapse and even cardiac arrest. Mild symptoms of poisoning can occur even on skin contact with the blue potato plant. So be sure to always wear gloves when working with the plant. If you have pets or children, it is better not to get a blue potato bush – or at least place it so that it is out of reach of children and animals.

However, the blue potato bush is edible for birds. On the other hand, the buds of the clove tree (Syzygium aromaticum) are perfectly suitable for human consumption. This shrub is rarely found in our latitudes, as it originates from the tropics and can only be cultivated here in tubs and with a bit of effort.