100% Perlite Media PERLITE

The Schundler Company
10 Central Street
Nahant, MA 01908
732-287-2244 www.schundler.com


reprint of an article from
Grower Magazine
February 28, 1991

Peat has come to dominate the market for substrates but, as David Hall and Chris Smith of the Scottish Horticultural Substrates Center argue, inert substrates warrant further development as environmental pressure gains pace.

Sphagnum peat dominates the horticultural substrates market in the UK, now estimated to be more than 2 million cubic meters a year and worth around 50 million. However, environmentalists throughout Europe are increasingly concerned about the use of peat in horticulture, arguing that harvesting causes the loss and destruction of ecologically fragile, wetland habitats. Their current campaign is receiving widespread media exposure and is likely to lead to a consumer boycott of peat and peat grown plants.

The industry, therefore, needs to take a closer look at materials which might act as substitutes. But a forward-looking industry which thrives on its initiative and innovation should not be content merely to consider peat substitutes; it should also strive to develop better alternatives.

Professional growers will not accept any substitute which does not match up to peat's excellent performance. Three criteria are especially important:

Matching Peat---Alternatives to peat should match the characteristics that make it an excellent raw material for composts. These characteristics are:

  • Excellent air/water balance
  • Freedom from pests, diseases and weeds
  • Acid pH
  • Resistance to physical and microbial decomposition
  • High buffering capacity
  • Low nutrient status
  • Low 'dry' bulk density
  • Guaranteed supply
  • Consistent quality
  • Competitive price

These demands have ruled out many pretenders to peat's throne, including the multitude of composted organic wastes, worm-worked manures, spent mushroom compost and many others whose initial nutrient richness and continued microbial decomposition are not under the grower's control.

The most closely controlled growing systems of all --- more controlled even than peat--- are those based on inert media and hydroponic principles. Hydroponic techniques like those based on the mineral substrates rockwool and perlite have already taken over from peat culture as the most popular methods of growing salad vegetables under glass.

There is no reason why the progression that took place in the glasshouse vegetable sector---from soil to peat to hydroponics---should not also take place in the amenity sector. Small-scale experimental work at the Scottish Agricultural College (Auchineruive) over the past six months has confirmed the enormous potential of semi-hydroponic methods based on perlite for producing the whole range of amenity plants: plugs, bedding, house plants and outdoor hardy nursery stock.

Inert Advantage--- Inert mineral media like perlite have a number of advantages over organic substrates like peat. One of the most significant (which was not exploited in the trial) is their complete lack of organic matter and so their very low microbial populations. Plant roots in perlite do not have to suffer the strong competition from microbes for oxygen as they do in peat. This offers the grower and (perhaps more importantly) the consumer the opportunity to stand perlite grown plants permanently in shallow water, with only beneficial effects on growth and ease of water management as consequences. Peat treated in this way would rapidly become waterlogged and plant roots would soon starve of oxygen. Future work with perlite will study pot designs which allow an internal reservoir to be maintained.

How Much Does Perlite Costs?--- The first question growers often ask about the pros and cons of a new introduction is "how much does it cost?"' An argument regularly voiced against peat alternatives is that they are more expensive. However, the higher initial costs of inert substrates should be set in context. Base on a 13cm pot, perlite only costs about 0.8p more than peat, but its sterility, consistent uniformity, and ease of water management are benefits which should easily outweigh such a small price difference.

Perlite-grown plants can stand in a permanent water reservoir because their roots are not competing with microbes for oxygen.


The preliminary study reported here was designed to develop a semi-hydroponic system for house plant production based on a very fine grade of perlite with 90% of particles less than 1 mm and an air-filled porosity of 13%. This was the first report on growing house plants in an all- perlite mix to the authors' s knowledge and so the formulation of base dressings and liquid feeds had to be based on a mixture of first principles and intuition.

Rubber plants (Ficus elastica Robusta) were chosen as the test species. Micropropagated plants, weaned in peat plugs, were potted on March 12, 1990 into 13cm pots of fine perlite containing one of four different base dressings, each treatment replicated nine times. Liquid feeds, specific to each base dressing, were applied according to need based on analysis. Growth and quality of the plants were compared with those in a standard peat mix given a 200 N: 200 K2O feed as required and an occasional 60mg/litre P205 supplement.

The plants were assessed on July 19. Ten objective measurements were made, including height to tip, maximum breadth, number of leaves on main stem, length and breadth of largest leaf, number of side shoots and intermodal distance. Subjective assessment of marketable quality was based on overall appearance including color.

Despite being a first attempt at using an inert substrate for this type of plant production, plants in three of the perlite treatments were rated better than those grown in peat on both objective measurements and subjective score.

February 28,1991

For more information about these and the many uses of perlite in hydroponic growing,
contact your local extension service, The Perlite Institute (www.perlite.org) or:

The Schundler Company
10 Central Street
Nahant, MA 01908
(ph)732-287-2244 (fax) 732-287-4185
email: info@schundler.com

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