Article for March 2007
& Text by Wilson Wong
by Lynnette Terh
on 3 Apr 2007
The familiar edible sweet potato - tubers (left) and heart-shaped
potatoes are best known for their edible tubers. Sweet and starchy,
the tubers are an essential ingredient in many local desserts.
Botanically known as Ipomoea batatas, the sweet potato
is a member of the morning glory family, Convolvulaceae and
is closely related to the morning glory vine (I. purpurea)
and the leafy vegetable, kangkong (I. aquatica). It is
not related to the true potato, which is a member of the tomato
perennial in the tropics, the sweet potato plant is a non-climbing,
herbaceous vine that is native to tropical America. Mature plants
produce purplish morning glory-like flowers. Most of us are familiar
with the traditional sweet potato tubers that have a light brown
skin, longish in shape which tapers towards both ends. Now there
are varieties from Japan that have reddish purple coloured skins.
When cut, sweet potato tubers reveal a myraid of flesh colors
- white, cream, yellow, orange, and purple. The sweet potato bears
alternate heart-shaped or palmately-lobed leaves, which are not
spared from being used as food. The young leaves are stir-fried
as a leafy vegetable with chilli and minced dried shrimps.
potato vines are extremely vigorous growers that quickly cover
up the ground surface, capable of smothering weed growth, thereby
reducing the need to weed! They are easily established, relatively
pest-free and rather tolerant of soggy soil conditions. These
characteristics make the sweet potato vine a very attractive groundcover
candidate! The indecisive vegetable gardener may want to consider
growing the sweet potato as temporary ground cover for a plot.
Once a crop has been selected, the vines can be easily cleared
and the leaves be used for food. If left long enough, there may
be tubers underground waiting to be harvested!
Locally, four varieties of ornamental sweet potato vines can
be found - 'Blackie', 'Marguerite', 'Black Heart' and 'Tricolor'.
'Blackie' has greenish or purple leaves that are deeply lobed.
'Marguerite' on the other hand has bright, chartreuse green
heart-shaped leaves. 'Black Heart' has also heart-shaped leaves
which are dark purple. 'Tricolor' is perhaps the most spectacular
variety with variegated, palmate leaves with splashes of green,
white, and pink. Unfortunately, it exhibits a less vigorous
potato plants are worshippers of the sun and they demand a location
with full sun to do well. Plants grown in a shady location will
produce leaves that are smaller and the leaf-to-leaf (internode)
distance will also lengthen. Ornamental varieties will produce
less colorful leaves. Tuber yield will also be affected. Sweet
potato used as a ground cover should be allowed to sprawl over
an open, unshaded area. Otherwise, growth can get sluggish and
the vines will not fill up the area fully.
(left) and 'Black Heart' (right) being used as a groundcover.
exceptionally particular with soil type, sweet potato grows
best in a location that has well-drained soil. Heavy clayey
soils need to be lighted with organic materials like compost.
Refrain from feeding with fertilizers rich in nitrogen as it will
promote excessive foliage growth and depress tuber yield for tuber
producing varieties. Sweet potatoes are hungry vines and a balanced
fertiliser should preferably be applied at the base of the bed
before planting. Potassium is critical for proper tuber production
and hence regular applications of a fertilizer with a higher potassium
ratio every fortnight would be useful. Some people use crushed
eggshells as well.
have a tendency to root at the internodes wherever they
touch the ground. Make it a point to lift the vines and
throw them back into the plot to prevent rooting. By allowing
the plant to root at multiple internodes will bring about
the formation of many small tubers at the expense of larger
should refrain from over-harvesting of leaves for food
from tuber producing sweet potato vines as this would
depress tuber yield.
of tubers can commence roughly about four to six months
after planting. Foliage and vines are first removed where
the young leaves can be used as a vegetable. The tubers
are then lifted carefully using a hoe (cangkul) from one
side of the raised bed.
Right: Roots appearing at the internodes when they
touch moist ground.
potato plants are most commonly propagated via stem cuttings.
A tip cutting that is roughly 30 cm long can be used and one can
request to take a couple of cuttings from any vegetable farm or
community garden. Each cutting should be spaced roughly 30 cm
apart in a raised bed. Keep the soil moist and it is normal to
witness cuttings wilting under extremely hot weather. Once cuttings
have rooted, sweet potato vines can be relatively drought-resistant.
intrigue children at home, one can grow a sweet potato plant
using a tuber bought from the local market, a glass jar and
several wooden toothpicks. First, stick three toothpicks around
the tuber near midway along the sweet potato so as to allow
the suspension of the tuber over the jar. The sharper end of
the tuber should face downward into the jar. Next, fill the
jar almost to the top with water and put it on a bright windowsill.
Within a week, the tuber will send roots down into the reservoir
of water and new shoots will appear on the upper end of the
tuber. It can then be transferred into a hanging pot to allow
the vines with ivy-like foliage to grow and then drape over
the sides. Alternatively, the entire plant with the tuber can
be transferred to be grown in a raised bed.
potatoes are seldom bothered by pests and diseases. The most serious
pests that one can encounter are weevils and beetle grubs that
will bore into the tubers. These can be avoided by practising
crop rotation and avoiding consecutive plantings of sweet potatoes
in a single location. For control of these pests, drenching of
the soil with an insecticide is the only remedy. Beetles, caterpillars
and stem borers may also cause some damage to aerial growth and
these can be eradicated relatively easily by application of a
Occasionally, unsightly brownish fungal spots may appear on the
sweet potato leaves. These can be prevented by having better air
circulation around the leaves and treatment can be carried out
with an application of a contact fungicide. Tuber rot can be prevented
by growing in better draining soil and using rot-resistant varieties.
Unfortunately, these special varieties are not easily available
to the home gardener in Singapore.
C.K. 1979. Grow Your Own Vegetables. Singapore: Times Books International.
Tindall, H.D. 1983. Vegetables in the Tropics. London: Macmillan