Making a Cactus and Succulent Mix



Horst Berger loves cacti. In fact you could say he’s a little obsessed. He has more than 1000 cacti in and around his Sydney suburban home. Costa visits Horst to find out more about the secrets of growing these prickly yet lovable plants.

Horst is originally from the German town of Lubeck and has been growing cacti since he was 10 years old. A favourite in his collection is Mother-in-Law’s Seat Echinocactus grusonii, which is absolutely enormous and about 40 years old. Horst loves its flowers and really enjoys the challenge of growing these plants from seed.


• To ensure his cacti grow successfully Horst makes a special potting mix, which combines a mixture of ingredients including perlite, pumice, charcoal, decomposed granite and palm fibre.

40 litres decomposed granite
20 litres scoria (5–8mm diameter)
20 litres of pumice
20 litres of quartz sand
20 litres of Perlite
20 litres of palm mulch
6 litres of crushed charcoal (1–8mm diameter)
2 litres of pelletised gypsum (3–4mm diameter)
½ litre superphosphate

• To make the mix Horst sieves the decomposed granite through a 1.25mm mesh and uses only the coarse material.

• He uses a palm mulch block that will give him about 65 litres of ‘expanded’ fibre. He prepares or expands this by mixing the following ingredients in 15litres of water:

30ml Wettasoil
50ml Seasol (or Sea Mungus in pellet form)
1 litre blood and bone fertiliser
50ml trace elements
100ml potassium

• The solution is used to expand the block of compressed palm mulch, which is then stored in a large, covered plastic drum for about eight weeks.

• Once a week, the contents are turned over. Twenty litres of this will then be used to prepare the cactus mix and the balance used for other potted plants. The cactus mix, once prepared, is left to stand for a further four weeks before used for potting.

• He also uses Maidenwell medium grade diatomite in the mix; up to 30 per cent by volume. (40 litre bags of diatomite are available in a few different grades – ‘fine’, which is 0.5–2mm in diameter and ‘medium’ which is 2–7mm in diameter. Coarser grades are also available.) Diatomite is a sterile, high silica growing medium which will absorb water equivalent to 150 per cent of its own weight. It typically sells for about $18–20 for a 40-litre bale.

• For alkaline-loving cactus plants, Horst adds limestone chips to the cactus mix. His seed-raising mixture consists of 90 per cent diatomite (fine grade), 9 per cent palm fibre (fine) and 5 per cent gypsum, in powder form.


• If you don’t want to make your own potting mix, nurseries stock pre-made succulent and cactus mix. It needs to be free draining and low in organic matter.

• Like all plants, cacti and succulents need a little fertiliser, but only apply it to the soil not the plant itself and be sure to dilute it. Horst suggests using a half strength fertiliser.


To find a cacti and succulent club near go to

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