First time with Disa, how much should it be fertilised
 

Picked up a Disa to try at a show yesterday and I asked the vendor lots of questions but forgot to ask how much it likes being fertilised.

For most of my orchids I use Rain Mix (aka MSU) at a weak concentration with every watering.

Would this be happy with something similar, does it like more or less at different times of year, should it be stronger/weaker? :scratchhead:

Exciting, Rosie! I'm also new to Disa. I already killed my first one, and giving the 2nd try. I'm assuming you are talking about stream side Disa (relative of D. uniflora). According to the ebook Disa companion, 100 micro-S (well it says 100 mS, but it is likely to be a typo) for every other week, and can be increased to up to 300 micro-S in the spring.

Ray has posted EC-ppmN conversion factor for MSU:
http://www.orchidboard.com/community...tml#post403341

So 100 micro S corresponds to 14.7 ppmN.

I looked up several scientific papers about Disa culture, and I'll see if there are some info there tomorrow.

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 ----------

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...

Philip, I don't know if you have seen this thesis (Danita Pienaar 2005), but I think it is freely available:

https://scholar.sun.ac.za/handle/10019.1/3042?show=full (scroll down to see the link to PDF)
or
This direct link may work.

The first chapter has some summary of cultivation, and here is some extract about fertilization.

- Du Plessis & Duncan (1989) Bulbous plants of Southern Africa - A guide to their cultivation and propagation, Tafelberg Publishers LTD., Cape Town.
Disa respond well to feeding, and recommend frequent, but very dilute feeding (e.g. Chemicult @ 1 teaspoon per 10 litres). Either foliar spray or drench

- Orchard (2000) Disa: growing international addiction to South Africa's pride. Amer. Orchid Soc. Bull. 69: 634-644
EC of 200 microS/cm (about 100ppm TDS) is preferable. But EC of 300 microS/cm is acceptable.

- Wodrich (1999) The Kiwi experience - Disas in New Zealand. S. Afr. Orchid J. 30: 54-61
Conecntrations up to a maximum of 600 microS/cm seems to pose no problems. High EC increases plant size and gerenal vigor, but high fertilization seems to prevent formation of tubers (flower and die) as Philip pointed out.

Pienaar's result is somewhat similar to Wodrich's observation. In the experiment, the lowest EC was 250-410 microS/cm and the highest was 440-1110 microS/cm. They used hydroponic (Ebb-Flow or drip system), so the EC was kept within the range. Higher EC -> larger leaves and plant, less root for a given amount of leaves. Also, there seem so be a trend to make smaller new tuber (proper statistics is missing to say this).

So, stream-side Disa can take quite a bit of fertilizer, but it is better to keep it at the low end.

Additionally, I summarized results about NH4 vs NO3 in another forum:
Slippertalk Orchid Forum- The best slipper orchid forum for paph, phrag and other lady slipper orchid discussion! - View Single Post - Disa aurata

There is another chapter about foliar feeding experiment, but I haven't read it yet. But the abstract seems to indicate that fertilizer with NH4 NO3 (ammonium nitrate) is more effective than that with urea for the foliar feeding.

If there was a way to triple like your post, I'd do it in a heartbeat!

Thank you very much! It is much appreciated!!!

It is a great and easy to follow thesis paper, (I gotta thank the author of the article for this, that is awesome!).

I will have to read this in greater detail after work. :)

Philip, I emailed you a couple more Disa papers (some scientific, others cultural advise).

Thank you very much! :)