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Plant a "carbon sponge" in your garden or home with the beautiful Spekboom

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Portulacaria afra. Picture courtesy www.newplant.co.zaPortulacaria afra. Picture courtesy www.newplant.co.zaThe spekboom belongs to a large and widespread family (Portulacaceae) which includes the popular summer flowering annual Portulaca, although this annual is not a South African species. Portulacaria afra has a growing reputation for saving the planet and recent research has dubbed the spekboom "an excellent carbon sponge" because of its ability to absorb more free carbon from the atmosphere than most other plants. Studies have shown that this amazing succulent can store more than four tons of carbon per hectare, creating what is called a "carbon sink" when planted in large plantations, and making it one of the best plants to grow in order to combat warming of the earth's atmosphere. In fact, this beautiful yet unassuming succulent has become so famous it even has its own Facebook page!

Portulacaria afra is found in warm situations on rocky outcrops and slopes in succulent Karoo scrub, thicket, bushveld, and dry-river valleys in the eastern parts of South Africa, from the Eastern Cape northwards into KwaZulu-Natal, Swaziland, Mpumalanga, Limpopo and further north into Mozambique. The spekboom is a strikingly attractive, evergreen succulent with its small round emerald-green leaves, borne on startling-red stems. In the garden it will grow moderately to a height of about 1.5 to 2m, but can mature into a small tree 2 to 5m tall. Although a succulent, the trunk and branches have a woody inner tissue, and the stiff, irregularly arranged branches will grow into a thicket if left unpruned. Heavy branches may break off, often rooting where they fall and starting new plants. In the wild, a myriad of small star-shaped pink flowers are produced in clusters at the ends of the branches from late winter to spring, although flowering in cultivation can often be erratic. Pollinated flowers are followed by tiny, papery and transparent 3-winged fruits which resemble pinkish lanterns, each with a single seed. The flowers are a rich source of nectar for many insects, which in-turn will attract many insectivorous birds. This plant is also called "Elephant Food" in the Eastern Cape because it forms part of the diet of the Addo elephants in the Addo National Park.

Various different forms are found in cultivation, most of which originate from the Karoo Desert National Botanical Garden in South Africa.

'Limpopo' is a large-leaved natural form which represents the northern populations which extend into the northern provinces of South Africa and Mozambique. It has much larger more ovate leaves that can measure up to 20 to 30mm long and 15 to 20mm wide.

'Prostrata' is a low-lying, decumbent form, growing 10 to 20cm tall, with small, glossy green leaves. This spekboom looks wonderful if allowed to cascade over a low wall or rockery, or planted in a Loffelstein type retaining wall, hanging basket or pot. It also makes a wonderful groundcover and contrast plant under Cycads or other form plants.

'Aurea’ is a compact, upright form with rounded leaves that go bright yellow in the sun. It is lovely in containers and a wonderful contrast plant in the garden.

'foliis Variegata' is a popular and highly adaptable variegated form with creamy-yellow mottled leaves and nearly horizontally branches that sprawl on the soil, seldom growing over 20cm tall.  This slow growing form is well suited to container culture and a beautiful contrast plant in the garden.

'Medio-picta' is a ground hugging form which grows slowly and can be planted in full sun to light shade. Its attractive stems are a bright reddish-pink and the small green leaves have wide white stripes down their middle, sometimes with little or no green. This great garden plant makes an excellent ground cover and also looks gorgeous spilling over containers or low walls.

'Variegata’ has a compact, upright form with white or cream edged, pale green leaves with pink highlights. It does not tolerate bright sun as much as the species and is perfect as a contrast plant in the shade garden and grows easily in containers.

‘Tricolor’ has a lovely pendulous habit and the green leaves are variegated with yellow and pink. It is very striking cascading down almost anything. This form may appreciate some shade, especially in very hot regions.

‘Cork Bark’ is slow growing with the main trunk having thick fissured corky grey bark, from which emerge reddish brown stems holding long emerald green leaves.  It can be planted in sun or shade and works as a great bonsai plant or small specimen shrub. Cork bark was selected by bonsai specialist Dave Bogan who first noted its fissured, corky bark in a Florida nursery in the 1960s. Its corky trunk was first thought to be caused by a fungal disease but later recognized as a natural aspect of the plant, with bright light and lean conditions seeming to promote the best fissured bark, but it should also be noted that this is a slow process, requiring considerable patience.

Portulacaria afra prostrate.  Picture courtesy www.newplant.co.zaPortulacaria afra prostrate. Picture courtesy www.newplant.co.zaPortulacaria afra prostrate. Picture courtesy www.newplant.co.zaUses:

Besides being excellent for binding atmospheric carbon, the spekboom is browsed my many wild and domestic animals, and is a favourite of tortoises. The leaves have a sour or tart flavour, and humans are also known to chew on the juicy leaves for their health benefits. It is also used in salads and stews, and it has been recorded that a small sprig of spekboom, steamed with a tomato bredie, imparts a delicious flavour. Also, the honey made from the flowers is reputed to have a remarkable flavour and texture. Traditionally the leaves are chewed to increase the breast milk of lactating mothers, and as a treatment for sore throats and mouth infections. The leaves are also used to quench thirst, and sucking on a leaf is used to treat exhaustion, dehydration and heat stroke. Crushed, leaves are rubbed onto the feet to relieve the pain of blisters and corns, and the astringent juice is applied to skin as a treatment for sunburn, pimples, rashes and insect bites or stings.

Portulacaria tricolor. Picture courtesy www.newplant.co.zaPortulacaria tricolor. Picture courtesy www.newplant.co.zaPortulacaria tricolor. Picture courtesy www.newplant.co.zaIn the Garden and Home:

The spekboom is so easy to grow and although it is known to be a great drought tolerant plant which is perfect for water-wise and xeriscape gardens, it will even grow in well-watered garden beds as long as the soil drains well. Because it is drought tolerant and also fire resistant, the spekboom is excellent for firescaping properties which are susceptible to wildfires. It is also a good soil binder, helping to prevent soil erosion, and is used for restoration purposes in semi-arid landscapes and thicket vegetation. It has also shown good results when grown as a "green roof plant", where much larger plants are able to be grown.
All forms of this versatile plant are easy to grow in containers and the cork bark form makes an excellent and handsome bonsai for indoors or outdoors. The low growing forms make excellent groundcovers and look spectacular if planted in in hanging baskets, or as part of a mixed succulent dish garden. The upright forms can be clipped into a hedge or informal screen, and the medium fine texture of their foliage makes a good contrast to wide-leaved annuals or perennials such as coleus or heucheras. The reddish colour of the stems also coordinates well with plants with red, purple or dark foliage.  

Portulacaria afra prostrate 'Gold' Picture courtesy www.newplant.co.zaPortulacaria afra prostrate 'Gold' Picture courtesy www.newplant.co.zaPortulacaria afra prostrate 'Gold' Picture courtesy www.newplant.co.zaCultivation:

Portulacaria is generally suited to all regions of SA but is not ideal to grow outdoors in heavy frost areas. It is an easy to grow succulent that is heat, drought and fire resistant, and can be grown in full sun or semi-shade. Although it is very drought tolerant, with adequate water it will grow much quicker and the foliage will be lusher, but be careful not to overwater, as it is susceptible to root rot in consistently moist soil. In the garden it can be watered together with neighbouring plants as long as the soil drains well. The spekboom is hardy to moderate frost and in the wild large plants survive the winter frosts by growing dense enough to provide their own natural cover. The tops of the plants will become burnt but the underlying layers will be protected. If your garden soil is fertile no feeding will be necessary except for a good mulch of compost each spring to encourage new growth. The spekboom takes well to pruning and can be clipped into shape as required.

This succulent will thrive indoors if placed in a warm room with bright light. Too much direct sunlight can cause the leaves to turn yellow or red at the tips – which some people prefer – but it may also burn the leaves. Therefore, it may require some experimentation with locations to find the perfect spot for your spekboom. Perfect drainage is especially important if you are planting into containers and unglazed pottery is best to allow for better evaporation of excess moisture. A regular potting soil to which liberal quantities of washed river sand is added can be used for potting. Don’t leave a saucer full of water underneath the container or the plant may rot. Rather, fill the saucer with fine gravel and place the pot on top so excess water cannot reach the drainage holes. Water your plant only when the potting soil is dry or almost totally dry, and in cold winter regions restrict watering to a minimum in winter. Feed potted specimens monthly during the growing season with a liquid plant food and repot when the plant has filled the container or the roots can be seen growing out the drainage holes.

Portulacaria afra 'Large Leaf' Picture courtesy www.newplant.co.za Portulacaria afra 'Large Leaf' Picture courtesy www.newplant.co.za Portulacaria afra 'Large Leaf' Picture courtesy www.newplant.co.za Propagation:
 
The spekboom is easily propagated from cuttings or truncheons which strike roots easily without a rooting powder and can even be planted directly into the ground where they are to be grown. Alternatively, cuttings can be taken in the normal manner and planted in washed river sand. Keep slightly moist in a warm shady position until the rooted cuttings are ready to be planted out, after four to six weeks.

Pests & Diseases:

This plant has few pests, but watch out for mealybugs, spider mites and whitefly, which can become, especially indoors. Like many succulents it does not tolerate some pesticide sprays. Petroleum-based chemicals should be avoided, or test first on a few leaves to be sure the material will not damage the leaves.

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