Computer problems but I'll try to get this out without it freezing!="Steve Johnson" post_id=377400 time=1598231546 user_id=4655]
Why isn't the same standard being applied to Nitrogen, then? Going with the Dyna-Gro 7-7-7 -- 2.1% is ammoniacal Nitrogen (NH4), and 4.9% is nitrate Nitrogen (NO3). If we take the Hydrogen out of the ammoniacal, and Oxygen out of the nitrate, it'll give us the actual N going into the plant, and IMO this is what we should really be looking at. If I'm wrong here, please correct me.
The 7%N in the fert is the percentage of the actual element available to the plant. The 7P and 7K is NOT the percentage of those elements available to the plant. To convert,.....Use 0.44 x the P2O5 listed (7) = 3.08% of the element P available to the plant. And 0.83 x the K20 listed (7) = 5.8% of the element K available to the plant.
Well yes and no. As you know, too much N results in bloated plants which are more prone to diseases and pests, too much P can interfere with trace element uptake especially iron and it can reduce flowering. Too much K is very rare and usually not an issue.My contention that a 1:1:1 NPK ratio is best for cacti refers to the ratio of fertilizer salts, and 99% of hobbyist growers will only go by that because they either don't know or don't care about the actual Nitrogen, Phosphorus, and Potassium. Does it even matter?
So given that the recommendation for strong, resilient and compact cacti which flower well, it is generally recommended that cacti should receive lowish N concentrations and highish K concentrations. From my own research the most desirable RATIO not the concentration, would be around 10 - 4 -15. In the US system that would be something like 10-9-18. The 15 % K is probably more important late in the season when light levels are lower because it strengthens cell walls and regulates stem elongation.
Yes. The actual concentration given is to be based on experience and trials. Obviously you don't want to over feed. The recommendations given on fertilizer packets has been worked out by the manufacturers to allow you to use as much as possible without adversely affecting the plant. This way they get to sell as much fertilizer as they can. The ppm or concentration should be worked out according to your environment, the type of mix you use and how often you water between feeding etc etc.He's right about that. Mike, you don't have any problem with math, but I'll break it down for the people who do. 7-7-7 means 7% Nitrogen salts, 7% Phosphorus salts, and 7% Potassium salts. We'll go through the numbers diluting 1/2 teaspoon of the Dyna-Gro 7-7-7 in a gallon of water:
- "Parts-per-million measures what you actually put on the plants. If you put 2-7-7 on without diluting it you would kill them, so it is pretty pointless to say you use 2-7-7 without saying how much you dilute it. Also pretty pointless to say you use 7-7-7 instead of 20-20-20 since they will both be the same by the time you put them on the plants.
Rather than give two or three different bits of information and expect people to work it out for themselves, just give the ppm and everyone knows exactly what it means. Except they don't because people have been conditioned since birth to think that numbers are hard"
1 gallon = 768 tsp., so we'll double that to 1536 half-teaspoons
7/100/1536 x 1,000,000 = 46 ppm.
Now we'll break down the two forms of Nitrogen. Based on Iann's understanding of it, 32 ppm. of the nitrate N is used up by the plant first, and 14 ppm. of the ammonium N is used up last. So, is the Nitrogen really too high? In this case, I think not.
I was suggesting the N was too high for the K (or better, the other way round) In other words I don't really think your N is too high but rather that I would increase the K to N ratio. The actual ''amounts'' (ppm) you give is up to you. It's the interaction between the N the P and the K I'm concerned with if that makes sense.
I was trying to illustrate that the P given in high P fertilizers was bunk. In Australia, because we use the N P K system, it means that some fertilizers with crazy amounts of P eg, 7, 14, 15 or something means I am giving 14% available P to the plant which is not only unnecessary but counterproductive. I think your fertilizer is fine and you should absolutely continue with it if it gives you the results. You probably have very good light levels in winter? That makes a big difference.Those two studies are fine as far as they go, but A. they're limited in scope, and B. they're too esoteric to be of any use to hobbyists who are trying to grow their cacti as well as they can. All I can offer is 9 years of anecdotal evidence showing that the fertilizer I chose has produced consistent results which are better than I could've imagined back in 2012. I also know that there's no such thing as a "right" way to grow cacti, and comparing notes with the shared experience of individual growers gives all of us the ability to learn from each other.
add the potassium to give you the ppm K you want. In your case, you want to double the ppm of K Something like that.
