Steve Johnson wrote: ↑Wed Feb 22, 2023 8:08 am
Just a followup thought here...
There are a few species in my collection that are mature enough to flower but never have (or at least not as they should):
- Tephrocactus articulatus papyracanthus from the California Cactus Center purchased in June 2011 -- no flowers yet.
- Tephro inermis also from the CCC purchased in May 2012 -- no flowers yet.
- Coryphantha hesteri from Miles' To Go received in July 2013 -- came ready-made with a set of 5 buds that went into bloom. 2 flowers in August 2014, after that no buds at all.
- Copiapoa laui from CoronaCactus Nursery received in July 2013 -- 1 big beautiful flower in October 2014, and that's it.
- Ariocarpus fissuratus also from CoronaCactus -- blooms every other year, and November 2022 was the latest. Could be normal for the species, but if it flowers again after a growing season of lower P at 0.3 this November...
Hi Jerry,
I have a few more cacti I'll add to the list:
- Astrophytum asterias from CoronaCactus received in July 2012. 1st flower in summer 2014, and a reliable bloomer until it stopped flowering last year. The species normally flowers in spring and summer, so I was thrilled to see this on 12/18/21:
- Astrophytum_asterias12182021.jpg (106.03 KiB) Viewed 4747 times
Maybe I shouldn't have been so thrilled. First of all, those flower colors appear "washed out" compared to what they normally look like -- example on 6/22/20:
- Astrophytum_asterias06222020_02.JPG (122.37 KiB) Viewed 4747 times
Second (kind of a red flag to me now), blooming well out of season. And the third red flag -- the plant aborted a couple of buds last spring, then no more buds after that. Unlike other Astrophytum species, A. asterias tends to be finicky about how it's grown. This leads me to wondering if mine got tired of being fed with 0.44 P after 10 years.
- Mammillaria guelzowiana from Miles' To Go received in July 2013. Also a reliable bloomer until it stopped flowering last year.
- Stenocactus lloydii also from Miles' To Go received in December 2013. Usually flowers late February-March, but no sign of buds that should've been setting by now.
It's possible that some species are more sensitive to a higher P/N ratio of 0.44 than others, and I think there may be a general sensitivity I won't know about unless and until I bring the P down to 0.3. If nothing else, the 2023 growing season should be an interesting test to see if the lower P leads to a noticeable improvement in all of my cacti by the end of summer. The test will begin once we get past this unusually cold SoCal winter.
Contrary to what I asserted here...
Steve Johnson wrote: ↑Fri Feb 24, 2023 12:39 am
MikeInOz wrote: ↑Sat Feb 18, 2023 12:42 amNo one knows what the affect of too much P on cacti looks like. The only way to know is to do a trial with blocks of identical seedlings and give each block ever increasing concentrations of P. But it would probably turn out to be rather pointless because we already know that we should not give too much P from the results of other trials for other plants. So why do it in the first place?
The trial for African violets showed flowering decreasing by 50% when the P/N ratio was increased from 0.14 to 0.44. If we stick to somewhere around 0.25 to 0.35 more or less, there will be no problems. [My emphasis.]
What he's basically saying is that cacti are just like all other plants in terms of their P requirements for optimal growth.
...I wonder if cacti really are just like all other plants in terms of their P requirements. Could it be that cacti do need lower P compared to nonxeric plants like orchids and African violets? This isn't just about flowering -- it's also about what excessive amounts of P could do to push cacti beyond their natural growth limits. From something I posted in "The Cal-Mag of My Dreams?", and I'll pull out the relevant quote:
Steve Johnson wrote: ↑Wed Feb 15, 2023 11:08 pmHere'a an item of interest I found called
Master gardeners: Desert soils and fertilizer by Lake Havasu City Master Gardener Steve Gissendanner (source
https://apnews.com/article/5e06475955f8 ... 2d491782c6):
- "Desert soils are often low in phosphorus as well. Phosphorus comes mainly from rocks, but most phosphorus is locked up in sediments and rocks, making it unavailable to plants." [My emphasis.]
This make a good argument in favor of the idea that a P/N ratio of 0.25-0.35 is optimal and anything above 0.4 is excessive for cacti being grown under cultivation.
When P is higher than N, that's a big excess, and even though we don't know what abnormal growth would look like, my guess is that you would see bloated weak-spined cacti that bear no resemblance to what they should look like according to type for the species. A P/N ratio of 0.44 is a much smaller excess, so I think it would take more than a few years before abnormal growth is apparent enough to be obvious. One thing we're not discussing here, but IMO should be -- the plant's longevity. Excessive P = shorter lifespan, and that could be the biggest problem when cacti are being fed with too much P in their diet. Of course that's merely conjecture on my part, and I don't know if this has been studied. But the excessive P-lower lifespan connection in cacti does seem logical.