Finally... (continued from last post!!)

The inquiring mind from my last post emailed me again with the following:
"Thank you very much for the info! I have a few remaining questions though. I keep my house at 77F/25C. I kept the ppm for the catnip at about 1100-1300 (about 2.2-2.6EC) and I wouldn't have thought I burned out the plants with that nute strength so I am leaning towards the problem being atemp problem or lighting problem. The plants receive full sun in the afternoon for about2 hours. Every thing else grows well.

1)Any sage like advice on temperature?
2)pH of 4.5 and ec of 4.5-5.5 for tomatos? Wow-thatseems low and high, respectively. I try to keep pH at5.5-6 and ec at 2-3. I have had good results with that but you have made me curious and now have to set upanother system to test!"

I responded:
"Hi again,
From what I've seen and heard, catnip survives relatively well in soils with poor nutritional quality. Why not do an incremental increase in ppm (starting at about 1 ppm for example) and work your way up? This way, at the first sign of adverse reaction, you can simply dilute the nute solution and note the last working ppm for future batches.

25 C is about the average optimal temperature! I can find no documentation on temperature optimums for catnip. Full sun in the afternoon for 2 h might increase the temp a bit, but shouldn't be a problem.... direct sun for 2 h also shouldn't be a problem... how close are your plants to the glass? Have you considered using something to diffuse the light (some people I know lightly soap their windowpanes to the height of the plants - this continues to let light through, but scatters it a bit so that it's not as direct).

In regards to the tomato nute solution, let me see if I can't provide a rationale for using the pH and EC I did. I used Plant Prod (7-11-27) supplemented with calcium carbonate. At an initial pH of about 4.8 (I see I previously typed in 4.5, which is a tad too low, so please make a note of this!), the calcium carbonate dissolves well and becomes available to the plant. Tomatoes in particular need calcium to build fruit and prevent problems like blossom-end rot. Over time, the pH of the solution will eventually rise, causing the calcium to precipitate out of solution. The pH can be brought down/controlled by topping up the nute solution on a regular basis such that the operating range is somewhere between 4.8 and 5.4. The EC is appropriately high; tomatoes require a lot of nutrients. However, when first transplanting new plants into a system, I have a rule of thumb that I always follow in order to prevent burning the plants: use half-strength nute solution for at least a week and gradually build it up to full strength over the second week.

Good luck!"

Finally... a question on home hydroponics!!

An inquiring mind asked:

"I would like to ask you a few questions about hydroponics. I live close to Phoenix, Arizona in the USA and have started a very small hydroponics system on my westfacing window sill.The 1st system is growing basil, chives, and catnip (all 3 catnip plants have died). The 2nd has tomato and stem-type onion. The house stays at 77F/25C. I use READYGRO SUPER PLUGS surrounded in Hydroton. TheReadyGro says it is made of "tree bark and organicingredients". I test the nute strength w/ a ppm meter. The ppm meter shows an INCREASE in nute strength themore it is used without me adding more nutes.I have tested 1 cup distilled water then tested thesame water 30 seconds later with 20 hydroton pieces init and the meter read a 2.5x increase in ppm, 10 to 25.
1)Because the readygro are organic, is it true theywill degrade and increase the ppm?
2)Why would the hydroton increase the ppm as whathappened in the simple distilled water test I performed?
3)What is the EC and pH and temp requirements forcatnip?
4) Does 1EC=500ppm?"

I answered:
"I asked around and found that in general, the requirements for catnip nute solution are 1.9 to 2.1 mS/cm with a pH range between 6.0 and 6.5 (and yes, 1 EC = 1.0 mS/cm). Also, just in case you were wondering, I find that an EC of 4.5 (to start, can increase this to 5.5 after acclimatation) and a pH of 4.5 (throughout) is good for hydroponic tomato nute solution.

I think what happened with your ddH2O (distilled deionized water - I assume it's deionized because of the effects you describe) is that the clay particles probably add ions to the water. This effect is most prevalent with deionized water! Try the same test using regular tap water and see if you obtain the same results. Although Hydrotron is supposed to be "neutral", it's still clay - a medium that's known to attract ions in soil solutions and release them under certain conditions. Another thing you might want to try is rinsing the pellets under running tap water (or, alternately, soaking them in distilled water) prior to your test, and definitely prior to using them, as there may be some chemical residue (for example, flame retardant) on the pellets.

READYGRO SUPER PLUGS are indeed organic, and can degrade under normal conditions. However, there are probably a lot of other factors that contribute to the changes in ppm and pH that you're experiencing, including uptake of nutes by your plants, release of root mucilage and plant byproducts into the nute solution, and increase in microbial organisms in the solution and rooting matrix. This is why it's important to monitor the pH constantly, as it's your key to ensuring the proper amount of nutes are available to the plants, and is also an effective method to prevent the growth of detrimental microbes. I would continue to add more nutes to the solution on the schedule you have, then simply adjust the pH up/down depending on the reading (the degradation byproducts from READYGRO SUPER PLUGS may not provide essential nutrients to the plants). The pH adjustment should bring everything to the levels required by the plants. "