Green Culture Singapore
Feature Article for May 2006
Text & Pictures by Matthew Cheng Huat Lim
Edited by Lynnette Terh
Online on 21 May 2006



In this article, let me share with all cacti enthusiasts a recipe of the cacti mix that I have concocted myself, as well as the different types of pots that I use to pot up the plants in my cacti collection. I also would like to discuss some issues regarding repotting, transplanting and watering.


THE IDEAL CACTI POTTING MIX

Let me first emphasise that there are many different types of cacti potting mix available commercially, each with a distinct formula. One cannot say which brand is better than the other.

Use the one that works best for you. Give yourself some time to try out the different mixes. You will be able to know which is the brand that is most suitable for your plants after some trial and error.

However, I find that most commercially prepared cacti mixes are quite expensive to purchase in large quantities. As it is quite easy to mix up a mixture from freely available and cheap components, why not try to prepare a cacti mixture yourself?

The most important feature of a cacti mix is that it must be free draining and it does not remain wet for prolonged periods, as the roots will very likely rot in such a situation.

MATERIALS FOR A HOMEMADE CACTI POTTING MIX


Above: From top/clockwise - Granite stone, pea gravel, fine gravel,
perlite, soil and the final potting mixture.

Granite Chips

Granite chips are used to line the bottom of a pot to allow for easy drainage, which is absolutely important for cacti. You can also use small-sized broken down clay or cement bricks instead of granite, so long as the material allows for easy drainage.

Cacti hate waterlogged "wet feet" conditions and their roots will tend to rot if they remain wet for too long.

Pea Gravel

These brown, hard pebbles are called "pea gravel" in Australia. These are more commonly known as "LECA" in Singapore. LECA are high temperature hardened clay particles, which are inert and sold in many different sizes. In Singapore, nurseries that specialise in hydroculture will have LECA for sale.

I use LECA pellets mainly to cover the surface of the pot, to make it look nice and neat. It also serves to hold down the particles of perlite that tend to float to the surface of the mix after some time.

Pea gravel may also be used as part of the potting mixture. Up to 5% LECA can be used in the final potting mixture so that its drainage is further improved. LECA will come in useful when the soil portion of the cacti potting mix is clayey.

Fine Gravel

Fine gravel is used as a substrate to line the bottom of fish tanks. Easily available in Singapore aquarium shops, fine gravel is used at a proportion of about 25% of the potting mix.

Perlite

Perlite are small, porous, white particles that are a result of pretreatment using very high heat. Perlite constitutes 25% of the potting mix.

Perlite is not be confused with vermiculite, which is more water retentive than the former. Vermiculite is not a good additive for potting up cacti.

Soil

The most suitable soil type for use in a cacti potting mix is one that does not contain peat.

Sandy soil is preferred over clay-based soil. If you buy clay-based soils, it is necessary to add more of the other components described earlier to make it more free draining.

Soil makes up a 50% portion of the total mix.

The Final Product

The potting mixture is made up of 50% of soil, 25% of fine gravel and 25% perlite. Pea gravel can be added to further improve water drainage, as described earlier.

By mixing the components in this manner, you create a mixture that will allow for easy drainage and for good aeration for the cacti roots.

The resultant cacti potting mix contains relatively low level of nutrients. It is therefore necessary to fertilise the plants with a liquid fertiliser during the growth period but not immediately after transplanting or repotting the cactus or succulent plant.

Use a fertiliser that has a low level of nitrogen, perferably below 5%. Granular, slow-release fertilisers are not recommended as they will remain in the soil for too long and may harm the roots, leading to rot.

TYPES & SIZES OF POTS FOR CACTI



Above: Plastic pots on the left and terracotta pots on the right.

There are 2 types of pots that are suitable for potting up cacti, namely, terracotta and plastic. There are pros and cons for using each type of pot. Terracotta pots are heavier, dry out faster and needs more frequent watering. Plastic pots, on the other hand, are lighter, making them easy to handle and keeps the soil moist for a longer period of time.

I use both types currently. I started out with terracotta pots at first, but now, I prefer to use plastic pots. Surprising trivial, everyone in Perth over here use black plastic pots, which, by the way, can be made to look shiny and new looking by applying some baby oil! This makes your pots more appealling when your plants are brought to society meetings and competitions.

The pot sizes I use nowadays are those that have a diameter of 100 mm. Most cacti can be transplanted into pots of this size and be left alone for 2 to 3 years. This is what you want, as you do not disturb the root system by frequent transplanting/repotting. If the plant is small, then use 50 or 70 mm diameter sized pots.


Above: The importance of having adequate drainage holes at the bottom of pots.
I have drilled extra holes in my terracotta pots for maximum drainage.


REPOTTING & TRANSPLANTING

I always remove the plant that I have purchased from its original pot as the mix they use often contains too much peat, which tends to retain water. It also allows me to check whether the roots of the plant are diseased or may contain mealybugs. In some cases, the roots have already overgrown the size of the pot and are protruding from the underside of the pot and need to be repotted.

To remove the plant, I first (especially in the case of plastic pots) squeeze the pot to dislodge the mixture from clinging to the side of the pot. Then I shake off as much of the old mix as I can, taking care not to damage the main tap root, before immersing the balance in a pot of water to allow remaining portion of the original mix to be washed off.

After that, you can snip off the diseased roots as well as portions of the root that may be damaged as a result. In the event that you find mealy bugs, you can wash these bugs off or spray them with "Confidor", an insecticide that contains Imidacloprid as the main constituent. Alternatively, you can simply use a cotton wool stick dipped in methylated spirit to remove these bugs from the roots.

After allowing the plant to dry off on a piece of absorbent paper for a few minutes, I then repot the plant in my mixture.

After repotting or transplanting, never water straight away! Leave the plant alone for about 7 to 10 days to allow the damaged roots to heal first before you water. It is important for the roots to heal to avoid fungal or bacterial and rotting problems. Do not worry - the plant will not die because you did not water!

As a general rule, allow only about 1/2 inch space between the plant and the rim of the pot. The reason is that you do not want to have too much soil and to maintain the balance between root system and soil ratio. This is especially important and significant if you water too much or too often.

The pea gravel I use on the top of the soil, like I mentioned earlier, is only for estatic purposes. It is not entirely necessary, some people say that because you have the pea gravel on top, you cannot really tell when the soil is dry and that the plant needs re-watering.

The repotted or transplanted plant should be kept in the shade for a few days before placing the pot in its final location.

HOW A HEALTHY CACTUS PLANTS SHOULD LOOK LIKE

The Echinopsis plant shown above is showing healthy growth since having been transplanted some 10 months ago. I have decided to dismantle and remove the contents of this pot to show root growth.

Notice how easily the whole contents can be removed from the pot. This picture shows how a combination of draining material, aerated mixture and top dressing makes for a suitable root growth environment.

A close-up look of the roots and how easily the mixture will fall away from the plant when immersed in water since the mixture is a combination of perlite, soil and small, hard particles.

This photo shows the plant after mixture has washed off in a pot of water. Root and root hairs are mostly intact and undamaged. The root ball is extensive - in just 10 months - healthy roots make for healthy plants!

WATERING

Using the pot sizes I recommended earlier, you can water them once a week or every 10 days or so, during the season that has fair weather and more often for the smaller-sized pots.

In Singapore when it rains often, be careful not to leave it wet for too long or too often, especially the hairer cactus species as they can easily develop fungal problems. As such, try not to water overhead Water the plant on the soil surface along the edge of the pot and not on top of the plant itself.

Last but not least, never allow the pots to sit in trays of water!




ABOUT THE CONTRIBUTOR

Matthew Lim first started being interested in Cactus and Succulents some 15 years ago. After his retirement to Perth in 1997 he has actively pursued his hobby mainly in cacti plants and currently has about 100 different varieties of cacti and succulents in his backyard.


COPYRIGHT 2004 - 2006 Green Culture Singapore All rights reserved
Best viewed with a resolution of 1024 x 768