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Can I use construction-grade expanded clay in place of brands like Hydroton when cultivating plants ?
Hi John ,
Thanks for this great question . In the pursuit of cultivating plants hydroponically , growers are constantly in search of ways to keep their cost of production low in order to maximize profits . There are certainly substitutions , alternative materials , and other components that may be used in place of brands marketed towards growers in order to keep production costs low . I would consider the following before deciding on your source material for expanded clay pebbles as a hydroponic grow medium . Hydroton and other brands of expanded clay manufactured for use in hydroponics are thought to be of food-grade , lacking other foreign chemical contaminants and materials that may be found in construction materials . Anecdotal reports that can be found on various grow forums indicate construction-grade materials possessing a higher alkalinity . This would require further buffering and less
predictability when soaking the medium and throughout your specific grow cycles . This alkalinity could be a result of exposure to limestone , concrete / cement , construction sand , mortar , and other materials . Quite often , the construction-grade clay is manufactured or co-packed in diverse manufacturing settings that are catering to other material manufacturers . You can be confident that when buying brands like Hydroton , the clay is manufactured in a dedicated environment free of contaminants . Beyond raising your pH , these contaminants may act to harm or entirely kill your crop at the drop of a hat with little time to remedy the situation . When buying in retail settings , the grower can also be confident of storage conditions of the clay and whether or not it has been exposed to other harmful chemicals . I would never buy a bag of expanded clay that was sitting next to a dusty bag of mortar mix . Another thing to consider would be the cation exchange capacity ( CEC ) of your source of clay medium . Clay manufactured for hydroculture is made to specific parameters suitable for growing plants , with a mostly inert quality . Construction-grade clay may possibly be fired at lower temperatures , resulting in a higher , lingering CEC . This attribute , if not kept in check , could very well lead to phytotoxicity . As mentioned in the article , the clay is pretty well inert , but even with Hydroton , one still needs to flush accumulated salts from the medium once in a while . I fear this issue could become compounded with higher-CEC clay . Standards in particle size are also important .
Construction-grade clay may be either too small or too large . If too small , the macro pore space may be too tight and thus result in compacted medium with less aeration . If the pebbles are too large , which is common with constructiongrade material , pore space may be too open and would require more diligent control of your irrigation flood cycles ( if using ebb and flow ). From what I can see on some manufacturer ’ s websites , constructiongrade clay may also be of a higher thermal conductivity than that of hydroculture clay . What this means is that , should you experience fluctuations in reservoir temperature , whether you are using ebb and flo , DWC , or other hydroponic culture , the clay would then act to hold and store whatever water temperatures it is exposed to . If you are gone for a couple days and your HVAC system suddenly fails , you may experience a surge in high water temperatures . A higher thermal conductivity in your medium would ensure the roots may be more prone to things like pythium , botrytis , gnats , and other pesky problems . With all this being said , I do believe in trial and error and further experimentation . I encourage you to trial both options . At the very least , you may benefit from monitoring a smaller identical set-up with construction-grade expanded clay . If you are able to mitigate the potential issues discussed above , then the lowered cost of production would only serve to make you a smart and savvy grower .
Happy cultivating , Zach Zeifman
Zachary Zeifman discovered his love for gardening while working for Homegrown Hydroponics / Dutch Nutrient Formula . Zach now owns and operates Soulgarden Farm , where he grows sustainable hydroponic and traditional soil crops . During the winter , Zach helps homeowners design and build hydroponic gardens to grow food year-round .
ALKALINITY
Alkalinity refers to the capability of water to neutralize acid . This is an expression of buffering capacity . A buffer is a solution that essentially absorbs the excess H + ions and protects the water body from fluctuations in pH . The presence of calcium carbonate or other compounds such as magnesium carbonate can contribute carbonate ions to the buffering system .
– water-research . net
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