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Hello ,
I love your website and publications ! I ’ ve been struggling to find the answer to a question about feed strength . I ’ ve noticed most feed schedules for hydro mediums like coco or stone wool call for much higher electrical conductivity ( EC ) rates than soil . I realize some soils are nutrient rich , but even some like Sunshine Advanced # 4 do not have much fertilizers inherent in the soil . What is the science behind this ? Why can I feed an EC of two in stone wool , but an EC of two in Sunshine Advanced # 4 would be detrimental ? Any input would be greatly appreciated !
Thank you , Ryan
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Hello Ryan ,
Sunshine Advanced # 4 contains some added fertilizers ( as well as naturally occurring salts in peat and coir ) to give early plant growth a boost . In the case of Sunshine Advanced # 4 , it has had lime ( calcium hydroxide ) and a starter organic fertilizer added . Lime is used to help correct the naturally low pH of peat . This mix is designed to be used without any added nutrients for the first seven days , as the nutrients in the product should be sufficient for early growth . After that , the grower irrigates with their own feed solution to supplement those fertilizers in the substrate . Because lime and fertilizer are already present in the soil mix , if a fullstrength nutrient solution is given in this early phase , particularly to young , sensitive plants , then the EC around the roots could rise to higher than optimal levels . However , after the first week or two , a dilute-strength nutrient can be applied to supplement the fertilizers in the product and , as the plants grow ( and fertilizers become depleted ), the EC of the hydro solution can be brought up in full strength . So , the main reason for the lower recommended EC when using these types of potting mix soils is to prevent salt build up in the root zone from both the fertilizers ( which are often slow release forms ) and the hydro nutrient solution . This process is easily monitored and adjusted — just check the EC of the solution draining from the base of your growing bags / beds / pots ( the leachate solution ). It is the EC in this drainage which is important — so if it is becoming higher than the recommended EC for your crop and stage of growth , drop the EC back in the feed solution . The combination of fertilizers already in the soil mix and nutrient solution will both add to the EC of the drainage . The fertilizers in the soil mix will gradually become depleted over time , so checking the drainage solution EC gives you an indication of when you need to increase your feed EC to full strength in the mix being used .
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Kind Regards , Dr . Lynette Morgan Suntec International Hydroponic Consultants |