Hi Karl,

Also check out this video by John Kempf that goes into more details:

https://www.youtube.com/watch?v=JWvLjSpHAKs&t=2494s

The blog post strikes me as strangely unhelpful compared to everything else John writes/talks about. I would not pay too much attention to it.

The target EC depends completely on what deficiencies you’re trying to correct. Also, I think we really should be having these conversations in term of Total Dissolved Solids (TDS). TDS is often approximately .5 x EC. So EC of 3800 uS/cm = TDS of 1900ppm. That’s 1900 grams of mineral per million grams of water. While the EC-TDS conversion is not completely accurate, it gives you a much more intuitive sense of how much substance you are dissolving in water.

An extreme example of how TDS depends on the deficiency, is if you would be correcting a boron and/or calcium deficiency. You need approx 150x more calcium than boron. A solution with TDS 1000ppm (EC 2000 uS/cm) of calcium works really well. Probably could do 2000ppm (4000 uS/cm) on some crops without problems. If you did 1000ppm of boron, it might kill everything.

You also have to consider how well a plant can absorb/adsorb the nutrient. I would guess that a plant would absord boron much easier than calcium simply because of molecular size…but I don’t know. I think plants typically absorb mineral nitrogen (not aminos) much easier than calcium for example. So even if you had the same level of deficiency in nitrogen and calcium, you would need 2-5x as much calcium to correct the same deficiency level….these are imaginary “for examples”…don’t go off my numbers.

All of this is to say that, whatever is your deficiency, google the target level for foliar spray for each individual deficiency. You can add most of them in the same foliar spray (especially if you make the pH about 6.0-6.5, the spot where most minerals are available). I wouldn’t be too worried about the total EC or TDS. I would be worried about each individual mineral exceeding the individual target….which is probably not even a surface effect burning, but rather forcing your sap to go from a deficiency to a toxicity.

And when you add up the individual supplements, the EC will probably not exceed 3800uS/cm anyway, because there’s very few minerals that are recommended to be sprayed at levels higher than 1000ppm (2000uS/cm). You’re not going to harm your plants from too high EC, you’re going to harm your plants from an induced toxicity of an

disclaimer: all my experience with foliar sprays comes from 1 farm that I’ve worked on for the last 2.5 years in San Diego, CA. I designed the farm specifically for ease of weekly foliar sprays. We do a foliar spray every week. I’ve never tried or needed to do a heavy foliar spray that could address a long term deficiency. If I have any recommendation though, it would be: get tooled-up so that foliar sprays are easy and cheap. Then you can run low EC foliar sprays without any hesitation. Then you can spoon feed nitrogen, phosphorus, potassium or calcium without damaging your soil.

• This reply was modified 1 year, 11 months ago by  Benny Thompson.