Earthworm tea gives soil life a kickstart

After much trial and error, a businessman at Hermanus, in the Western Cape of South Africa, has developed a method of producing “tea” from earthworm castings on a scale large enough to be used in agriculture.

Organic fertilisers and pesticides are not all that popular with farmers because they are inclined to be inconsistent, spoil easily and usually cannot be continuously produced on a large scale.

Dr. Andrew Southey, a retired veterinarian, property developer, and former newspaper owner from Hermanus, has, after much experimentation over the last 6 years, developed a method of producing top quality “tea” from worm castings on a large scale.

Dr. Andrew Southey, retired vet and newspaper owner, in the nursery where he keeps his earthworms in cow manure.

Apart from doing research, and having to discern what was fact or fiction on the internet, he also made good progress with the help of a few coincidental observations. Today Valley Earthworms, his “factory” in the Hemel-en-Aarde Valley in the Western Cape, is made up of a shade net greenhouse with thick black plastic sheeting as a floor surface.

Andrew says that the shade net protects the earthworms from birds. He uses cow dung from a nearby dairy as the nutrient medium. He believes that the quality of his product is determined by the consistent quality of the manure and the fact that it contains no additives. “My system can help to restore and rebuild the biology of agricultural soil.”


Andrew says that although it has been customary over the past 60 years to form an opinion of fertilisers based on their chemical composition, the chemical analysis of the worm tea is of secondary importance. “What is of greater importance is the biological composition of the tea as far as the living and organic components are concerned.”

He says that the living component is easy, as microbes can be counted, but it will take a long time to unravel the science behind organic components. “At this stage, we can only measure the effect on plant growth by testing how the worm tea accelerates the germination of watercress. Two samples of his worm tea accelerated the germination by 60% and 65% respectively.

Earthworns in the nutrient medium – cow manure.

In 2012, he did in fact carry out a chemical analysis of the earthworm castings from which the tea is made, and the results can be seen in the TABLE below. Andrew feels however, that the results are not really relevant as worm tea is more about soil biology and the beneficial microbes that are naturally produced.


Nitrogen (%) Phosphorus (%) Potassium (%) Calcium (%) Magnesium (%) Sodium (mg/kg) Manganese (mg/kg) Iron (mg/kg) Copper (mg/kg) Zinc (mg/kg) Boron (mg/kg)
2,3 1,27 0,98 2,82 1,04 3343 454 6159 59 555 52



He keeps the worms, castings and cow manure medium in open plastic crates that allow ventilation from the sides and the bottom. Microjets keep the manure and worms damp and flush the castings tea over the black plastic on the floor and out of the enclosure.

The floor of the ‘factory’ slopes so that the tea runs down to an underground tank at one end. From there it is pumped to tanks. Oxygen is introduced into the stream of tea being sprayed into the tanks by means of an inverted Venturi spray that draws air in.

Earthworm “tea” in a tank where oxygen is drawn in.

Andrew’s clients are primarily grape and berry farmers who bring their own tractors and tanks, but there are a few domestic gardeners who buy smaller quantities of the worm tea in their own containers. He also supplies tea to the Starke Ayres nursery group.

Andrew shows the tanks in which the worm tea is stored.

He is currently able to produce 10 000 litres of worm tea a week. Although the favourable climate of the Hemel-en-Aarde Valley is conducive for the earthworms, he plans on building a barn in the future where the temperature can be better controlled, especially in winter when the worms grow slowly.

He sells the tea for R2.20 (K1.50) a litre for quantities over 1 000 litres.


Andrew says that experiments with the tea have shown that it increases the proportion of usable leaves in butter lettuce. He also showed us photos of mint leaves with a richer colour and more intense flavour, and an arum that looks as if it is on steroids. Sceptics will say it is easy to get good results in a domestic environment, but Andrew’s earthworm extract is also used on a large scale by grape farmers in Ashton and Hermanus.

The owner of the Excelsior estate near Ashton, Peter de Wet, says he has been using Andrew’s worm tea for the past five years. Each September he applies 100 litre/ha via his drip irrigation system. Besides the stem thickness of the new vineyards treated with the tea being 19% bigger than those fertilised conventionally, the vines are healthier and have better root systems. Peter says that they apply the worm tea as a standard practice on their 220 ha vineyard.


Johan Montgomery, a viticulturist with Hamilton Russell Vineyards (HRV) in the Hemel-en-Aarde Valley, says that they have been following organic cultivation practices for the last two years and have been focusing especially on soil improvement.

One of the biggest problems with organic cultivation is the availability of nitrogen for the plants. To this end, soil fertility must be promoted and this is where the use of worm tea comes in. “What I like about Andrew’s set-up is that he thinks analytically and can tell you exactly what it is he is selling.”

Johan Montgomery, a viticulturist with Hamilton Russell Vineyards, is very impressed with the results he gets from the earthworm tea.

Johan adds that he is happy that HRVs vineyards in the Hemel-en-Aarde Valley are located close to the earthworm tea factory as the worm tea contains living organisms and must be aerated and used as soon as possible. He says he has observed that Andrew is trying to keep the process as organic as possible and he has confidence in the use of cow manure as it has passed through the rumen of the cattle.

Although HRV is actively following an organic farming practice, Johan hopes that they can get more support for the testing of organic substances and their correct use, and that the Agricultural Research Council and the Faculty of AgriScience at Stellenbosch University will do more research in this regard. They currently administer the worm tea and other organic substances such as Verte Guano and products from Agro Organics, hoping that it is at the right time and in the right quantities.

“We have lots of questions about this, and any answers we do get come from overseas universities and agricultural advisors, especially America. I would like it if we had a good study group that travelled from farm to farm and shared their experiences. We still don’t know how to interpret our results yet. What we do know is that the worm tea gets soil life going.”

Johan says that he has seen a difference in the soil. Fewer weeds occur where the tea is applied and the natural grasses have started to grow. Up to now, they have been applying the worm tea mainly during the budding season and after harvesting, especially after rain, but he says he is not sure if this is necessarily the best time.

“I reckon that the soil microbes will be more active and will benefit more in cool, damp soil as opposed to the dry, hard soil in the summer months.”

He is looking forward to the harvest from their 3 ha of young vines which received worm tea in the first week of January 2016 after 30mm of rain fell.

He believes that there must, in any case, be a mind shift with regard to the fertilization of vineyards. “Maybe we should wait until autumn and then feed the soil and vines well. Ensuring an adequate supply of nitrogen to the plants is our greatest problem. We trust that if the soil life is correct, the other trace elements will sort themselves out.”

Johan says that a farmer who moves toward a more organic approach becomes more attentive to the details of crop management. “One is inclined to look at what is happening in the soil and which weeds start growing because weeds can be indicators of poor soil.

“We must take steps to improve the soil in the same way that we were responsible for neglecting it, but there has to be an affordable and simple way that can be managed easily.”

ENQUIRIES: Dr Andrew Southey,



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