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!"