Potting compost for M. luethyi on own roots

I've just acquired three rooted cuttings of M. luethyi and am wondering what the right compost is for them. I've grown M. luethyi on a graft before, but have found it difficult to keep the scion from drying up, as the graft has often broken as a result of the expansion and contraction of the body at the join.
So now I'm trying them on their own roots, and wold like to know what compost mix has given you the best success.
I have sterilised garden soil; sharp sand; 2-5mm horticultural grit; peat; leaf compost; and volcanic grit (bims).
I know they come from a rather gritty but compacted habitat, and that they can be very wet at times and very dry at others.So I am tending to growing them in a purely mineral soil, probably pure volcanic grit, but maybe with some sharp sand as well.
Advice would be very welcome.

Good evening Chris,

Chris43 wrote:

>>>

So I am tending to growing them in a purely mineral soil, probably pure volcanic grit, but maybe with some sharp sand as well.

<<<

that seems to me to be the right substrate.
However, I would omit the sand - compacts the substrate and fills the desired gaps between the pumice.


Best wishes

K.W.

Thanks KW, I did wonder about the sand so I guess it'll just be bims then!

Chris43 wrote:

Thanks KW, I did wonder about the sand so I guess it'll just be bims then!

Hi Chris, How did this treatment turn out?
I have a luethyi in gravely mix and last summer it did precisely nothing!

I've kept them over the winter, giving them some water to keep them plump. So far, so good.But they haven't grown a lot....

And fertilizer?


Best wishes

K.W.

Not over winter, but yes, fertiliser with the normal summer watering. I use a tomato fertiliser sold in the UK under the brand "Tomorite", at half strength.

Hi Chris,
As that suggested mix is very similar to a bonsai recipe, I wonder if a bonsai fertiliser might be the order of the day. I use Green Dream on my trees. It is totally organic. N.6%, P. 5%, K.7%, Mg.4% + trace elements. It comes in granular form and washes into the soil. Only downside, being organic it does have a bit of a smell.

Like all my cacti, my luethyis are in pure pumice (bims), nothing else. The luethyis on their own roots don't get any water from about halfway September until the end of April. Only a few overhead sprayings before that in the spring. This year, I watered them for the first time on April 26, but buds had been visible for several weeks already. After that first watering, they swell up extremely fast. Two days after that first watering they have become twice as big!
I only heat my greenhouses when the temperature goes below -1 or -2°C, and my luethyis will get an occasional frost.
Grafted luethyis need a little bit of water during the winter / early spring, but the amount depends on your greenhouse temperatures in the winter. The cooler, the less they need.
In nature, they grow in a pure gravel substrate, in a region where there will be frost from time to time in the winter months. But in that dry season, they will be completely invisible, withdrawn in the gravel.
Because I live in the north of the Netherlands, the spring arrives rather late and the first watering in more southern locations ahould be done earlier than at the end of April.

Wolter ten Hoeve.

Hello everyone,
At first I had my Mam. luethyi's aswell in some organic mixture mixed with larger pumice and diatomaceous earth.
Since they are in pure pumice they are doing quite better!