The oleander (Nerium oleander), also called rose laurel, is the only species of its genus and belongs to the dog poison family (Apocynaceae). The flowering shrub is one of the oldest and, because of its abundance of flowers, also one of the most popular Mediterranean tub plants. It originated in Morocco and southern Spain and is now found throughout the Mediterranean, India and China. The evergreen shrub was already appreciated in antiquity, as documented by Cretan murals from the 14th century BC. The oleander came to the United States about 500 years ago. At that time it was reserved for the nobility and rich citizens who decorated their orangeries with Mediterranean beauty.
The evergreen shrub can reach a height of two to four metres and a width of up to three metres.
The fleshy, leathery, lanceolate leaves grow up to 20 centimetres long and about three to four centimetres wide. There are three leaves at each shoot node – botanists speak of a whorled leaf position here.
On the branched shoot tips, umbels form from several flowers. The wild forms each have five petals and flower pink or white. Due to various cultivars, oleanders are now available in over 400 varieties and many colours: light and dark pink, salmon, light yellow, white and red. In some varieties, the flowers appearing from June to September are full or have a delicate fragrance. Caution: Oleander belongs to the dog poison family (Apocynaceae) and is highly poisonous.
Colourful oleander: Some varieties have yellow or apricot flowers.
For a rich flower the Mediterranean stars need a sunny, wind-protected place. The more sun the oleander gets, the more blossoms it will produce. In cool, rainy summers, oleanders therefore flower considerably less. Stuffed varieties should be placed away from rain as the full flowers can absorb, stick and rot the water.
Classical potting soil with peat is not suitable for oleanders. The plant grows best in a predominantly mineral, calcareous substrate with a high clay or loam content.
Oleander is very thirsty, so you should water the tub plant abundantly in summer. On very hot days, large oleanders should be poured up to three times a day. It is best to place the pot on a coaster with a high edge that catches the excess water. The oleander can absorb this during the day and often only needs water once a day. Since the oleander grows naturally in floodplains, wet feet do not bother it – the pot can therefore stand up to a third in the water.
Oleander does not tolerate rainwater for long periods of time – this causes the soil in the bucket to become too acidic. The plant loves calcareous soil and therefore also calcareous tap water. Tip: Do not overdodoze your plant, but always water oleanders close to the ground, as moisture from above can damage the flowers and promote the development of oleander cancer.
You must fertilize your oleander regularly to make it bloom abundantly. So treat your plants to high-quality liquid pot plant fertilizer once or twice a week from March to September, which you add directly to the watering water. This ensures beautiful green leaves, dense foliage and vigorous new flower formation.
Since oleanders are very vigorous, a young plant must be placed in a new pot every year. The optimal pot for the shallow-rooted oleander is wide rather than high. Choose a pot that is about five centimetres larger and add pot plant soil, a part of clay granulate and some lime. Tip: If you want to repot large oleanders, you should tie the crowns together beforehand and water the root ball well – this makes the plants easier to handle and easier to remove from the plant container.
Oleander has a high ornamental value due to its long flowering period and its evergreen foliage and is often placed in bright corners and niches. As the plant is very vigorous, sufficient space should be available. Alternatively, oleander can be cultivated as a high trunk. Oleander is suitable for the sunny balcony, the terrace and the cold winter garden in an appropriately large bucket. It can be combined as a tub plant with laurel, olives, bougainvillea and numerous other Mediterranean tub plants.
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There are different reasons for cutting oleanders and also different types of cutting. The potted plant is fast-growing and well tolerated by cuttings. Oleander can be cut back at any time of the year. When is the right time, you can therefore largely decide for yourself. If the plant obviously forms fewer flowers and new shoots grow across the crown instead of outwards, you should definitely use scissors to control your plant, but for a lush flower you should only cut if necessary. The older branches tend to balding from below and often carry leaves only at the branches. Also the joy of flowering diminishes with the years. A rejuvenation cure takes place in spring. Cut back about one third of the oldest shoots to a length of about 20 centimetres. Individual disturbing, sagging or bald branches can be removed at any time throughout the year.
A pruning should only be carried out before moving the plant into winter quarters if the plant is either infested by scale insects or has become much too large. Of course you can also remove sick shoots. You should be careful with this pruning, as the plant has already planted the buds for the next year.
If necessary, an oleander can also be “put on the stick”, i.e. it is radically cut down. This may be necessary, for example, because of a strong pest infestation or because the oleander is glutted from below. Late winter is the best time for such a radical cutback. The plant will regenerate quickly and grow beautifully bushy. In this case, however, a new flower is not to be expected until the following year, as all flower buds that have already been laid on are removed during pruning. After a strong pruning back into the old wood, the oleander always forms only vegetative, flowerless shoots in the first year. A slight pruning by a maximum of one third of the shoot length leads to the formation of shorter new branches, which open their flowers around the end of July. Important: Wear gloves during all incisions, as the toxic latex that escapes irritates the skin.
Since oleanders are frost hardy only to about -5 degrees Celsius, the plant must be protected from excessive frost in winter. The ideal place to spend the winter is a cold winter garden or unheated greenhouse, a so-called cold house. Alternatively, the oleander can also be dark wintered in the cellar or garage, but temperatures should not rise above five to ten degrees Celsius. Rule of thumb: The darker the room, the lower the wintering temperature should be. In order to prevent infestation by scale insects, a low room temperature is recommended even with good lighting. A temperature between two and ten degrees Celsius is ideal. In closed rooms you should ventilate once a week. First the plant is cleaned out: Remove coloured leaves, withered flowers and damaged or diseased twigs. You should then check the oleander for pests. If the plant is infested, take countermeasures such as pruning or treatment with pesticides. If it is too large for winter quarters, you should also cut it back. If possible, however, we recommend that you wait until spring before pruning, otherwise the oleander may sprout too early. Check them regularly for scale insects in air-dry rooms. Water occasionally, as the root ball must not dry out completely in winter. It is normal that the oleander loses many leaves in the dark winter quarters – they drift again in spring.
If you live in a milder region, such as the North Sea, the Ruhr area, the Lower Rhine, the Rhine-Main area, the Moselle valley or near the Oberrheingraben, you can also overwinter the oleander outdoors by covering it with a fleece hood and placing it outside in a shady, wind-protected place with a well insulated pot. A location close to the house wall is ideal. To keep it warm enough, the first step should be to ensure good floor insulation – for example with a polystyrene plate under the plant pot. If you do not have too much space, you can tie the branches of the oleander together with sisal cord. This is also very practical because it makes it easier to wrap your plant and pot with coconut mats or bubble wrap and protect them from frost. Tip: Some nurseries offer a hibernation service for tub plants. So if your oleander has grown a little too big, just ask the gardener you trust. Here the plants are also optimally cared for over the winter.
Oleanders come in many colours with single or double flowers, sometimes even with variegated leaves (for example ‘Splendes Variegatum’). If you want to avoid the classic shades of pink, you can opt for the white ‘Alba’ variety or the red ‘Little Red’. Stuffed flowers display ‘Madonna Grandiflora’ in white, ‘Luteum Plenum’ in light yellow and ‘Mrs. Roeding’ in salmon colour. For those who like it gaudy, the dark red variety ‘Algiers’ is the best choice. Papa Gambetta’ is a compact, very easy-care variety with orange-red flowers. Particularly large flowers of about seven centimetres carry ‘Roseum Plenum’.
The variety ‘Alba’ has simple, pure white flowers (left). However, there are also varieties in which the flowers are filled (right).
There are different methods of propagating an oleander: by cutting, dividing, refining and sowing. The easiest way to propagate oleanders in spring is to use head cuttings, which are produced when the plant is cut anyway. Peel the twigs and place them in a water glass or root the cuttings in a pot of growing soil in a warm, bright place. When the first strong roots have formed, the cuttings can be converted into a pot of pot plant soil. Older plants can also be propagated by dividing the root ball. Cut back the newly formed plants slightly when potting, they will sprout again quite reliably. The other two methods are not recommended for the hobby garden and should be left to the expert.
Various pests and plant diseases can make life difficult for the oleander. At the beginning of May the first infestation with aphids threatens – the oleander aphids are easily recognized by their honey-yellow colour. Dark sooty mildew fungi often appear as a result. Silvery speckled leaves indicate spider mites. Woolly webs in the leaf axils and on the underside of the leaf indicate wooly and mealybugs. The infectious oleander cancer caused by bacteria can be recognised by small black spots surrounded by a light-coloured edge, which later bulge and break open, as well as by black twigs and crippled thickenings on the flower twigs. If your oleander already suffers from this disease, you should remove all infected leaves at an early stage and cut the damaged shoots back into the healthy wood. Tip: After cutting out the affected shoots, disinfect the scissors with 70 percent alcohol from the pharmacy to prevent infection of other plants.