Green Culture Singapore
Feature Article for November 2006
 
     
 
Text by Tan Boon Kiat
 
 
Pictures from
matthew1381, bluefly, ladybird, Tanya, noodle, victorIIIMd,
Ifurita, limxuanhong & wilson
 
     
 
Online on 30 Nov 2006
 


WHAT IS A CACTUS?

The word "cactus" is actually derived from the Greek word "Kaktos", which is actually a species of a spiny thistle belonging to the daisy family (Asteraceae).

(a) Cacti leaves have been reduced to spines in order to reduce the rate of transpiration during photosynthesis. The spines have 2 functions. First, they help to protect the plant from thirsty animals since the plant is full of sap. Secondly, the spines help to reflect the light rays of the glaring hot sun to prevent burns.

(b) Cacti have swollen stems to store water in order to survive in deserts with very little rainfall.

(c) Cacti have areoles which are characteristic of cacti as it is from these where spines, flowers or offsets will arise.

(d) Cacti have one of the most beautiful flowers among flowering plants. Some are so vividly coloured that they are almost inflorescent in order to attract insects for pollination under the glaring hot sun in a desert.

 

TYPES OF CACTI

(a) Cactus with ribs


Above: Parts of a ribbed cactus, Parodia.

Ribs help to shade the cactus from the hot desert sun at any part of the day. Flowers usually rise from the areoles near the apex depending on the cactus genera.

(b) Cactus with tubercles


Above: Parts of a cactus with tubercles.

Tubercles help to shade the cactus from the hot desert sun at any part of the day. It should be noted that flowers for this class of cactus ie the Mammillaria genus, arise between the tubercles and not from the areoles.

(c) Cactus with pads


Above: Parts of a padded cactus, Opuntia.

Like the ribs and tubercles, pads help to shade the cactus from the hot desert sun at any part of the day. Cacti belonging to the genus Opuntia have an upward growth habit. Once the pad has matured, it will stop growing. New growth will appear from the areoles of this matured pad and the process starts all over again. It should be noted that some of the genera have glochids which are actually a collection of very fine spines which may cause rashes to people with sensitive skin.

 

WHAT IS A SUCCULENT?

Above left: Aloe mitriformis is a leaf succulent.
Above right: Opuntia monacantha variant is a cactus.
Below left: Pleiospilos nellii is a leaf succulent. It is virtually stemless.
Belw right: Crassula perforata is also a leaf succulent.

The word '"Succos" in Latin means juice or sap. Thus, a succulent is a plant with water storage organs thereby enabling the plant to survive over a period of drought. Water can be stored in their leaves, stems and roots. They do not have spines.

Some succulents exude a milky sap when damaged. It should be noted that a cactus is a succulent but a succulent may not be a cactus. Cacti are stem succulents since water is stored in their stems. They do not have leaves and their roots are not fleshy too.

 

GENERAL CULTURE OF CACTI AND SUCCULENTS

(a) Light

Light is the main problem in many high rise apartment gardeners as not every one of us is blessed with a sunny balcony or a common corridor. Most cacti and succulents require at least 6 hours of direct sun or very bright light in order to stay compact. Lack of light will cause them to etiolate which will make them vulnerable to pests and diseases later. Most of their flowers require good light in order to open fully.

Personally, I find that most cacti and succulents hate to be grown under the shade of other plants. They like to be grown in an open space with no obstructions. On the other hand, houseplants do not like to be grown with them either and will be stunted in the direction where you place the cactus. They dislike spiny plants that tear their leaves.

(b) Soil

Soil has to be very free draining in order to grow them successfully as any pockets of stagnant water in the soil medium will cause roots rots. In high rise apartment gardening, it is crucial for the soil to be dry up by the third day after watering. Commercial mixes contain too much peat which is bad for cacti and succulents. Peat is too wet when watered and too dry when dry. Besides, it is very difficult to wet peat after it has dried up. In countries with low humidity, they make very suitable potting media but in the tropics, they break down easily and you may need to repot your cactus annually. Cacti and succulents dislike root disturbances and thus, it is not wise to undergo this operation annually. It is better to use loam-based potting mixtures as they are generally free of peat. Sadly speaking, most of the imported cacti and succulents sold in our local nurseries are potted in peat and it is recommended to repot them in a loam-based mix.

Above left: Most of the commercially available burnt earth is too fine. These fine particles need to be removed before use as they will cause future drainage problems.
Above right: Aquarium gravel which can be acquired at all aquarium shops.
Middle left: I usually use top soil as a substitute for aquarium gravel for the hardier cacti and succulents to save cost.
Middle right: Perlite will break down after a year and drainage may be affected. Repotting may therefore be required.
Below left: Peat should be avoided in all cactus and succulent potting mixture.
Below right: The resultant mix of 2 parts sifted burnt earth and 1 part top soil. Note the grainy texture of the soil mixture.

I prefer to mix my own soil for my cacti and succulents as follows: Sifted burnt earth (50%) and diatomite (50%). Of course, this is not the only mix that you can use. However, it is recommended to use at least 50% of soil which can be your burnt earth or any commercial cactus mix. The other 50% will comprise soiless medium for drainage enhancement like aquarium gravel, perlite, vermiculite, coarse sand, charcoal chips etc in varying proportions. You have to experiment the type of soil mix that is suitable in your area.

(c) Watering

It is very common to hear advice from nurseries that cacti and succulents require very little water and can survive weeks with no water. Cacti and succulents contain at least 75% water and sometimes I just wonder how the poor plant can grow well when there is no water in the first place. They need water just like our houseplants.

Do not forget they are not in the desert. They do not have long roots to search for underground water. They are confined in that little pot that you give them. If you do not water them, who will? Some of you may be surprised that desert rains are in fact very heavy and can last for days or even weeks. During this period, the whole desert will be in full bloom and most of the plants will grow, bloom and even fruit before the soil turns dry again.

Golden Rule

Water them generously when they are in active growth and sparingly when they are dormant or resting.

How to know my cactus is growing?

The spines at the apex, which is the growing tip of the cactus, will suddenly start to turn to a very bright red or yellow depending on the cactus genera. Then a cluster of spines will appear at the apex and it is now time to water your cactus.

Protect from rain

Always protect your cacti and succulents from rain as too much rain will cause our beloved plants to rot especially when they are resting.

When to water?

Always water your cacti and succulents when the top inch layer of the soil has dried up a little. You should water in the morning to prevent any possible fungal or viral infection.

How to water?

Water your cacti with a container containing a long nozzle. You can also use a pressure jet to water your cacti taking care not to wet the stem. Never hose down your cacti and succulents like your houseplants. Aim the nozzle at the side of the pot to allow the soil to absorb the moisture. Dry soil absorbs water very fast.

 

POTS

Clay pots are proven to be better than plastics. If you can afford it, go for it. Beware of overpotting. I have seen a small cactus barely 6cm across potted in an eight-inch pot. The soil takes too long to dry out and may cause the cactus to rot. Always pot the cactus no bigger than half an inch between the cactus body and the edge of the pot. Stagnant soil provides breeding grounds for root mealy bugs.

What happen if I do not have a small pot?

Grow your cactus in very well drained mix with a thick layer of aquarium gravel, perlite or sand at the bottom of the pot under a very bright location in an airy place. Something like a desert.

 

FERTILISATION

You may be surprised that desert soil is very fertile. Who says cacti and succulents do not need to be fed? In fact, you should feed them generously at half strength of the recommended dosage stated by the manufacturer weekly for good results. I prefer soluble fertilisers as the organic ones may burn the roots when the cactus is resting. Use a low nitrogen fertiliser if you can. For myself, I use a generic plant fertiliser for my cacti and succulents to save cost.

 

PESTS & DISEASES

(a) Root Mealy Bugs

Other than overwatering, root mealy bugs is the number one killer of our cacti and succulents. Root mealies like to attack cacti and succulents and it is very difficult to eradicate them. Prevention is better than cure. I always water my cacti and succulents with a solution of malathion weekly to prevent any possible attacks from the root mealies.

(b) Scales

It is unlikely that your cacti and succulents will be infected with scales if they are grown in good air and sun. White summer oil is very effective in removing them as the film of oil depletes the pests of oxygen intake thereby killing them instantly. It is white summer oil. Not super summer oil or any other mineral oil. The traditional white summer oil is harmless to the delicate tissues of the plants. Make sure your cacti and succulents are well watered before you spray them with a solution of white summer oil and water. Spray them in the early morning or late evening when the sun is not so strong.

(c) Rots

Rots are caused by overwatering and incorrect cultivation practices. Of course, the cooler growing cacti and succulents genera will tend to melt in our warm tropical nights.

 

 

 


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