The few things I have to offer are the following:
1. The N must be very low.
Too high a nitrogen level, and your Disa will not do well. Which seems to be corroborated by what Hildegard Crous mentions in her book, (page 43 in "Grow Disas"). She doesn't give out a numerical value in terms of how many ppm the N needs to be, but it doesn't seem to be very high.
2. K must be the highest of the three in ratio.
They seem to naturally come from low N and higher K environments. I've not found any scientific articles that directly links nor documents this to any species of Disas, the only thing that offers this clue is a pedology book about various South African soils, ("Soils of South Africa" by Martin Fey), and a mineralogy book, ("Introduction to Clay Minerals" by Bruce Velde).
Most of South Africa is very rocky. The rocks where
Disa uniflora come from are an ancient low-grade metamorphic quartzite-type sandstone, generically called "Table Mountain Sandstone". This sandstone has some K in it because of the clay minerals that were present in the rock during its formation. Nitrogen is something that the water they grow near probably dilutes a great deal. When they say the places where Disas grow are nutrient poor, they're most likely referring to nitrogen, not anything else.
Everything I mentioned above is very much evidenced when I was growing
Disa sagittalis. It did the best when I grew it using a fertilizer where the N-P-K ratio was 0-10-10. The other orchid fertilizers I used didn't force the orchid to form tuberoids.
Special note: Do not confuse clay minerals for clay particles, they are not the same thing! I'm not talking about clay particles, I'm talking about minerals such as illite, montmorillonite, or micah. Minerals are present in these rocks, but not in terribly large quantities. These phyllosilicates play a role in ion exchanges and mineral availability. The quartzite in the rocks are for the most part inert, but the phyllosilicates in the rocks are not.
I also don't think phosphorous is very abundant in their natural environment either, but i think it's more abundant than nitrogen is.
3. From what I've seen of
Disa uniflora,
Disa tripetaloides, and
Disa aurata; all 3 species grow slow during the winter. The fastest growth occurs during the spring/summer. Even though they are considered evergreen, they follow a seasonal pattern of growth. So, yes, it would make sense that less fertilization is needed during the cooler months compared to the warmer months.
Again, I don't have numerical values, but fertilization would be according to this readily observable seasonal behavior pattern.
4. Fertilization should be minimal. You must force them to conserve nutrients or they will not form tuberoids. Forcing them to form tuberoids is the ideal situation. This phenomena is not only mentioned in Hildegard Crous' book, "Grow Disas", (page 43); but I have witnessed it myself on all three species, multiple times. Too much freely available nutrients almost always equates to no tuberoid formation for all three species. I don't have a specific numerical value, but I can tell you it's pretty low.
5. They don't grow sopping wet. Allow them to dry to dampness, then water again.
6. They seem to grow better in plastic pots than clay pots.
---------- Post added at 12:01 PM ---------- Previous post was at 11:08 AM ----------
Quote:
Originally Posted by naoki
So 100 micro S corresponds to 14.7 ppmN.
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That kinda still sounds like a little bit too much N, imo. Idk, I could be wrong...
If only there was a good way to conduct a controlled experiment cheaply...
First time with Disa, how much should it be fertilised
Linear Mode
