Being a soil derivative the pot-soil was susceptible to soil-borne diseases such as Early Blight and Late Blight – a few sawdust containers also developed similar fungus maladies. About 40% of that specific block of plants grown in pot-soil developed fungus problems, which was rectified quickly, mainly with copper hydroxide to prevent it spreading.
Sawdust 50% / Perlite 50% performed slightly better than sawdust on its own. The Perlite added better water-holding capacity to the medium and slowed the drain of water and nutrients, causing plant growth and fruit formation to be better than sawdust only, but still poorer than Perlite on its own, specifically when comparing fruit size and number of fruits per cluster. From an economic point of view, it is a less expensive combination.
Fruit clusters grown in 50% sawdust and 50% Perlite.
Tomato cluster grown in a combination of sawdust & Perlite.
It is important to note that the data was collected on a daily basis and harvesting will be a decisive element of this experiment to analyse overall yield and quality per medium started on 15 December 2010 (90 days from sowing). The total harvest to date of 1,631 kg of ripe tomatoes is a trend, not a final indication of medium performance. Nevertheless, some conclusions can be made to predict the overall results due to various trends in plant performance.
The largest tomato was 402g grown in sawdust.
(click to enlarge diagram)
Conclusions
From all the tested mediums, palm pith and Perlite performed best in terms of production per plant, fruit size and weight. The combination mediums performed slightly behind with the exception of the palm pith / Vermiculite / Perlite mix, which was not far behind. The sawdust as a one-off medium performed reasonably well, but with considerably lower fruit size and weight. The pot-soil / Perlite mix performed worst in all categories.
The primary consideration as to which medium to use is economic, taking into account that some mediums are re-usable. The trial will test later the long-term effect on crops grown in re-usable media. It’s important to note that results will vary, depending on the hydroponics method used.
Ben Safronovitz
About the author
Ben Safronovitz graduated from agriculture school in Israel and has practised horticulture in South Africa since 1992. He specialises in soilless culture and has undertaken several experiments with various growing media and cultivars in South Africa and Israel. Ben is a lecturer in hydroponics at the Lifestyle Centre in Johannesburg, South Africa.
Acknowledgement
A special thanks to Camdeboo Farm, Fourways, Johannesburg, for providing the site and infrastructure and hosting the trials. Website: www.camdeboofarm.co.za
References
• W.R.Carlile, The use of composted materials in growing media, International Symposium on Growing Media, ISHS Acta Horticulture.
• D.Maragatham Jeyaseeli and Samuel Paul Raj, Physical Characteristics of coir as a function of its particles size to be used as soilless medium, American-Eurasian J. Agric & Environ. Sci.,8(4):431-437,2010 ISSN 1818-6769, IDOSI Publ.2010.
• Palm Pith Manufacturer data sheet.
www.lignocell.com
• Dr David A. Hall, Role of Perlite in hydroponic culture, Pershore College Horticulture, UK. http://www.perlite.org/perlite_info.htm
• Horticultural uses of Perlite and Vermiculite.
http://aggie-horticulture.tamu.edu/greenhouse/nursery/guides/ghhdbk/media.html
• Evaluation of coco coir as compared to sawdust for tomato crop production. http://www1.agric.gov.ab.ca
• Sakata- Malory, Indeterminate tomato.
