Until recently, the Carissa genus of shrubs contained around 100 recognized species, but many have now been assigned to other genera or simply as a synonym.
Native to tropical parts of Africa, Australia, and Asia, Carissa grows as a shrub or small tree. It has white, star-shaped flowers, followed by plum-like berries that are either purple or deep red.
This evergreen perennial is grown both as an ornamental plant and for its fruit. The fruit is used in some parts of Asia in both cuisine and medicine.
This species was introduced to the United States in the late 1800s. Originally, it was grown for its nutritionally rich fruit, but its importance quickly shifted to its value as an ornamental, landscaping addition.
|Scientific name||Carissa Carissa macrocarpa|
|Common names||Natal Plum|
|Height||2 to 10 m|
|Width||4 to 5 m|
|USDA Plant Hardiness Zone||Zones 9 to 11|
|Native to||Africa, Australia, and Asia|
|Blooming season||Mainly Summer, slight flowering all year|
|Plant specific features||Fragrant flowers, thorns, plum-like fruit|
How to Plant and Grow a Carissa Bush
Where to Plant
Carissa is useful in gardening and is a good choice for a hedge or privacy screen, due to its sharp thorns, attractive flowers, and interesting fruit.
This is a moderate to fast-growing shrub and takes around two years for the plant to be sufficiently mature to bear fruit.
If you want ground cover, then there are low-growing varieties of Carissa available that make a dense and decorative carpet.
A small Carissa variety can be planted indoors as a pot-grown plant. But it needs to get plenty of sun. Because of its thorns, it can be dangerous to place the container indoors where it might hurt passers-by and children in particular.
When to Plant
Best planted in late fall or during the winter.
Carissa Shrubs Care and Maintenance
Carissa shrubs like sandy soil, and it must be free-draining. If the soil doesn’t drain well, its roots will rot and the plant will die.
This is a plant that tolerates coastal conditions and tolerates salt. It isn’t too fussy about pH values. Carissa will tolerate slightly alkaline soil, although it prefers slightly acidic or neutral soil.
Too much water will kill a Carissa. It is a shrub that is very susceptible to root rot. In between watering, the soil should dry out completely. Make sure that excess water drains away freely.
Different varieties will tolerate and require different amounts of watering. Generally a monthly, or at the most bi-monthly, watering will be sufficient. Carissa shrubs are fairly tolerant to drought conditions.
It isn’t necessary to fertilize Carissa. But, an annual application of a slow-release, general purpose fertilizer will help to keep the shrub healthy. It will also encourage optimum flower and fruit production.
For the best flowers and fruit, plant your Carissa somewhere that receives a lot of suns. The less sun it receives, the fewer flowers and fruits you will have. It will tolerate a partially shady site but at the expense of blooms.
Pruning and Repotting
If you want to make your Carissa into a tree, you can do this by pruning. If you prune your shrub to keep it as a tidy, shapely plant (either tree or hedge), you will also increase the number of flowers and fruit.
Sometimes, it is necessary to cut Carissa back. This may be if it is growing as a hedge and its thorns are too close to passers-by, posing a risk of their being hurt.
If you propagate from seeds contained within the fruit, there is no guarantee that the plants produced will be the same as the parent plant. It is much more reliable to take cuttings from the stems and root these. Stem cuttings can be taken at any time of year.
The use of hormone rooting powder will speed up the rooting process. Simply dip the 6-inch cutting into rooting powder and insert it into a tray filled with sand.
The roots should develop fairly quickly, and you should then transplant them into trays that are filled with a mix of equal parts of sand and compost. Be careful not to overwater, but keep the trays moist.
Ideally, provide bottom heat under the trays as this will encourage top growth. As soon as top growth begins, you can plant the new Carissa shrubs into their planting positions.
Pests and diseases
Carissa doesn’t really have any pest problems. Any aphids that you spot can be removed if desired with horticultural soap. The biggest risk is root rot, a fungal disease caused by soil that is too wet, or overwatering.
Temperature and Humidity
Carissa is a shrub that is sensitive to the cold. For best performance, it needs to be kept over 20° C in the day and over 18° C at night. Even established Carissa shrubs will die if the temperature falls below -3° C. Young plants are even more tender.
Carissa shrubs are tolerant of dry air if they are sufficiently watered. They will also tolerate humidity in the air, providing the soil is not soggy.
Other Uses for Carissa
This shrub attracts birds and butterflies. If multiple Carissa is planted for a hedge, then birds will use its dense, evergreen foliage and thorny branches for nesting purposes.
As well as using the fruit for jams, jellies, sauces, and preserves, the fruits of the Natal plum are high in iron. It is somewhat misleading to call them plums, since they are not, botanically speaking, plums. And, Natal plums do not taste like plums!
In African medicine, the root of C. edulis is used to treat chest and respiratory problems and a significant source of income for African farmers. This variety has thorns that can be 70mm long!
Unfortunately, because the “plums” of Carissa have a short shelf-life, their viability as a crop is somewhat limited.
Types of Carissa You Can Grow
Carissa carandas or karanda is grown for its fruits, which are edible when ripe, and poisonous when green. Once ripe, the fruit is sometimes rather tart and resembles a large cranberry with a slight flavor of strawberries.
It can be eaten raw when picked or alternatively made into a preserve like jam, sauce, or jelly. In India, it is used to make a spicy pickle. It is rich in calcium and several minerals, as well as being high in Vitamin C.
The Carissa fruit does not ripen at the same time. So you have to pick them off individually, once the plum is dark red or purple. You can store them in the fridge until you have sufficient to use.
Carissa macrocarpa or Natal plum is known in South Africa as num-num. This is a tropical fruiting, evergreen shrub, mostly grown for its beautiful and fragrant flowers, but also for its small, cranberry-like fruit.
Because it has sharp, formidable thorns, it can be used as a privacy hedging plant.
A subspecies “Green Carpet”, also known as dwarf Natal Plum, is a low-growing, evergreen variety of C. macrocarpa very suitable for low borders or dense ground cover. You will also see this variety growing in formal clipped gardens.
Carissa bispinosa grows up to 5 meters tall and has fragrant, white, star-shaped flowers. This variety has forked thorns along its branches. Its fruit is red and known as forest num-num. Carissa bispinosa grows at relatively high elevations, either in forests or wooded areas.
Carissa spinarum is also known as the conkerberry. It’s a large, multi-stemmed shrub, very common in Australia. Confusingly, it is known in Australia by many names, including black currant, and grows as a noxious weed in agricultural land.
In parts of India, this shrub is called wild karanda, which comes from the botanical name C. carandas. The fruits of the conkerberry are only edible when ripe. The unripe fruit is poisonous.
Useful if you want to plant an edible hedge or screen, Carissa is a relatively easy plant, providing you have the necessary climate to maintain sufficiently high temperatures throughout the year.
*image by simonapavan/depositphotos