Hi Fred,
We have 3 comparison photos to review:
- Old_Man_of_the_Andes_comparison_photos.jpg (103.04 KiB) Viewed 1685 times
The photo on the left is from the nursery you mentioned -- badly neglected due to very infrequent watering as you said. Nutrient deficiency is obvious to the well-trained eye. I'm really glad that you saved one, and the Old Man of the Andes you rescued isn't so bad. However, the triangular top growth isn't normal. Compare it with the photo from llifle.com on the right, and top growth pointed out by the box is normal. Corking on the base -- also normal, but your plant does show premature corking. Lack of adequate watering does have something to do with it, but that's only part of the problem, the other part being excessive P in the Espoma 1-2-2 fertilizer you're using. We'll look at it again:
- Cactus.png (276.66 KiB) Viewed 1685 times
The oxygen in P2O5 and K2O supports the plant's health, but it has no nutrient value, so all we're concerned about is determining the amounts of elemental P and K available to the plant. Once again, the calculations are:
2% P2O5 x .436 = 0.872% elemental P
2% K2O x 0.83 = 1.66% elemental K
N = 1 is the constant for determining NPK ratios, so the Espoma's 1% N makes it easy -- 1-0.872-1.66. The balance between N and K is great, but P is way too high. A significant consequence of excessive P -- reduced stem
and root growth. Even though your Old Man of the Andes has 1" of new top growth, it should be filled out more than it is, and that's due to excessive P.
My fert of choice for 11 years had been Dyna-Gro All-Pro 7-7-7, so we'll take a look at its P:
- 7% P2O5 x .436 = 3.05% elemental P
With N = 1 as the constant, the P side of the ratio comes in at 0.44 -- not terribly excessive, but still too high. When Dyna-Gro discontinued the 7-7-7, I replaced it with General Hydroponics FloraMicro 5-0-1 and FloraBloom 0-5-4 at the beginning of the year. Okay, both ferts combined gives us 5-5-5, which means the same problem with P higher than it should be. What I'm doing there is supplementing the GH ferts with an ammonium sulfate-potassium sulfate stock solution, then adding the right amount of stock solution to my watering solution. End result -- the P side of the ratio is 0.29, well within the acceptable range of 0.2-0.4. Improvements in the stem growth of my cacti this year have been pretty amazing. Another consequence of excessive P is reduced flowering or no flowering at all. Compared to years of higher P in the 7-7-7, I'm enjoying the best flowering year ever thanks to the lower P in my new fertilizer regimen.
Fred, if you're up for making the switch, I'll be happy to give you the recipes and instructions for the GH ferts plus their supplemental stock solutions. Probably too late in the growing season to do you much good now, but you'll have plenty of time to prepare for next spring. The only problem I can foresee with your Old Man of the Andes is new top growth filling out next year, which will leave you with a sort of "pinched in" spot on the stem caused by the Espoma's excessive P. Maybe not a problem if you don't mind that, but you do have another option to consider:
- Cut the stem well below what I'm calling the "pinch point". Give the exposed tissue a liberal dusting of sulfur powder and let it form a callus. If the root system is healthy, your Old Man of the Andes will grow a new head on the cut. You can either let the new head continue growing as-is, or cut it and root it when it gets bigger.
I realize that option seems kinda drastic, but the good news is that you won't have to make decisions either way anytime soon.
) The problem isn't that far advanced and I'll be go to hell if I'll listen to someone on the internet telling me to throw it away,or chop it up 
There certainly are circumstances where pups would be fitting. And I believe you give a lot of consideration before recommending that. But here is the "good side" of the cactus in question as of today.
