In container media, pH increase results from neutralization of H+ in solution by the supply of usually either HCO3- or OH-, depending on the source of liming material (In the case of most container gardeners this will be fertilizer, though some that make their own soils are now using dolomite or other sources). Changes in pH subsequently affect a soil's cation exchange capacity (CEC). Changes in CEC affect a substrateÂs capacity for binding nutrient cations, with an increase in CEC allowing more cations to adsorb to the substrate particles (not a good thing). As a result, an increase in pH associated with lime additions often results in decreased macro-nutrient and micro-nutrient availability in both bark and peat-based media. A study by Haynes and Swift (1985), and by Peterson (1982) listed pH 4.0 to 5.2 as the optimal pH range for nutrient availability in soilless substrates. A recent reading of a paper on pH's effect on container grown nursery and ornamental material submitted for a master's degree in horticulture supports the finding that container-grown plants gain most biomass when grown in media with a pH like that listed above - much lower than you might think. From this, it's pretty simple to extrapolate the conclusion that rain water in the pH range of 4.0 or even a little lower is not likely to present much (or any) difficulty to plants unless they are lime-loving plants. If a hobby grower tells you he manages the pH of his container media, you can be very suspect of his veracity. Container substrate pH fluctuates wildly and is affected by a number of variables, so even checking daily with a reliable pH meter will leave the uninitiated scratching their heads over what is causing so wide a variance. How can we possibly make corrections when readings are so likely to be "all over the place"? As an illustration, my "management strategy" consists of using an acid forming fertilizer for those plants that appreciate a low pH, and a base forming fertilizer for the very few plants I own that prefer a high pH. I own neither a pH meter nor a moisture measuring tool. Figtree - If you're still hanging here: Yes, nutrients will be washed from containers at varying rates, and substrate pH does have an effect on which will be lost first because nutrients become most soluble at (in) a particular pH (range). A review of the chart I provide in the link will give an idea of what nutrients are most soluble at different pH levels. Al Here is a link that might be useful: Let's go see the chart

Hi Johnny, I have studied your case, so to speak and understand pretty well what you are dealing with in Romania. Looks like you are doing fine so far, except the lack of calcium and Magnesium (Sulfur). The only thing I'd leave out is the vinegar. If you can't (or don't want) use phosphoric acid or nitric acid, take citric acid instead. You should find it in powder form in some drug store or pharmacy. >>This gives me in the end, at least on paper an NPK of 18-7-21 [actual elements not K20 or N03)You mean P205, not N03, I guess? Are you sure about having those values in actual elements? I'm asking this because the specs of your products are not expressed in actual elemental content but in P205 and K20! Anyway, can you give me your final formula of each element in PPM? Even better of both products. That will be much easier for me anyway. There is a way to complement your nutrient with Mg, Ca and S. You need the following raw materials: CaCl (calcium cloride), MgSO47H2O magnesium sulphate (fertilizer grade, not medical grade) and calcium nitrate. I guess I understand your way of proceding with gram/liter and can give you clear instructions how much of each component or product (mentioned above) you need to add (in gram) to your existing products, to get almost exact PPM of Mg and Cl as well as S you need. To do this accurately, I need your 'analyses' in PPM (each element provided) of both products, though. Ideal PH for lettuce is between 5.5 and 5.8 and EC should be between 1.0 and 1.5 mS. Which means that you seem doing well concerning this point. Well, as long as your PH has no tendency to climb and your nutrient isn't evaporating to quickly (which induces raise of EC). PS: As your variety of lettuce is called "lolla rossa", which I know from Europe, the red/purple color of the leaves and stems seems pretty normal, as rossa means red (in Italian), - doesn't it? ;-) Please give me the result of your previous maths from both products and investigate about the required products and I'll do the necessary maths for you. Cheers Mate!

Hi brickza, I am using a similar technique (actually plant bags of different sizes and pots) to grow determinate tomato plants and other various crops. I also use perlite (or rice hulls) mixed with potting soil for the purpose. Except that I use this method as a final destination for my depleted nutrients - actually alternate depleted nutrient solution with "fresh-one" plus occasional watering. I used to have an extended drip system (to little waste) installed for the purpose, but have switched to manual since the production of this part has decreased. Most depleted nutrients are now used for bush and tree seedling production, which thrive amazingly well in it (as they fix nitrogen from the atmosphere and are anyway very forgiving in matters of pH, nutrient quality and composition). Anyway, the hybrid system with soil/perlite mix has proven to be not only a simple, economical and effective method, - but also very forgiving and hassle free. The soil part is promoting natural ion-exchange and self regulating pH in the root zone. Besides that, nutrient temperatures are apparently not so much of an issue. I would recommend to simply water your plants once a week, (or in your case between nutrient changes) that should be sufficient. Build up of "unused" nutrients is anyway overrated from my understanding and experience. With a potting soil/perlite mix it seems to be even less of an issue. I'd keep nutrient concentrations reasonable, though. In fact I guess that nutrient/salt build up is mostly the result of people pushing and overdoing it with nutrient concentration. I've never knowingly experienced it in any kind of system nor with any medium. I remember having read an older study about tomatoes grown in both, amorphous substrate (was it perlite?) and potting substrate/soil, a while back. Both fed with a standard drip system. There was no notable difference in growth and crop size/quality and no issue with the plants grown in "potting soil". No indication for salt build up in the potting soil either. Also your strategy with having only a small amount of nutrients seems fine to me, as you don't need to worry much about permanent changes in concentration. A frequent and (almost) complete change of a small amount is sometimes the better alternative. As I don't know the reason why you actually recycle or have your system "automated" (have you?), but I guess you could even simplify things and try/consider drip to (little) waste as well. Why? Well because if you dose the spent nutrient amount well, there is little loss and you can extend your "garden" easily and without any technical change or modification as there is no need for a run back then. Just a suggestion that seems useful to me in this particular case. Cheers and good luck with the final results, Lucas

I'll let the real experts chime in, but IME it's not uncommon for tomatoes' bottom leaves to die off as the plant grows. In this case, my guess is that these babies are ready for transplanting and my be a little root bound. Plants do sometimes shed leaves to maintain balance with the size of their root systems, Otherwise, they look very healthy to me! :-)