Yesterday on the German version of my blog someone asked me which conditions my Lithops gracilidelineata have. The question aimed specifically at the soil I'm using for them.
With that I realized that I haven't really talked about that in detail yet. Especially not for single Lithops species in particular.
Home grown Lithops gracilidelineata (5 1/2 years old)
You can find and read up on the history of my (home grown) Lithops gracilidelineata here: http://plant-whisperer.blogspot.de/search/label/Lithops%20gracilidel.
And of course, there is the general Lithops page http://plant-whisperer.blogspot.de/p/lithops-facts-and-trivia.html where I talk about my experiences with sowing Lithops and avoiding the biggest mistakes.
But now let's get to the details of my gracilidelineata:
When I sowed them in 2007, I had just read about fungus gnats and other mean specimen who are all out to get your delicious seedlings. So when I prepared the pots for my gracilidelineata seeds, I did the following:
I laced the bottom of the pot with a layer of mineral soil (e.g. volcanic soil) and covered it with a layer of quartz sand. On top of that I put the main soil, a special cactus soil that already contained some sand (but not enough) mixed with the same amount of fine quartz sand. And on top of that I put another layer of fine quartz sand.
The two layers of mineral soil on top and at the bottom of the pot will keep fungus gnats from getting into the soil and laying their eggs in there.
I dowsed the whole pot in water until the sand at the top was moist, and then I sowed the gracilidelineata seeds onto the top layer of quartz sand. I covered the pot with plastic wrap and put it under my energy saving lamp in the living room.
So my gracilidelineata seeds had constant moisture, 14 hours of light per day and temperatures of about 18° Celsius.
They germinated within a few days at which point I started to remove the plastic wrap for hours at a time until I could finally leave them without the cover altogether.
At this point the little Lithops will have grown visible roots that will probably not have the strength of growing into the moist quartz sand on their own. To help them get up and to avoid evaporation along their roots, I carefully covered the roots with more quartz sand and propped the tiny Lithops seedling bodies up against grains of sand.
At this point the mineral cover of the regular soil is crucial because now the seedlings are at their tastiest for fungus gnats.
So far the seedlings have only had contact to mineral soil (quartz sand) and the only "food" they got came from their seeds.
Once I had covered the roots and propped the seedlings up, they gained enough strength to dig their roots into the soil. Here, after about three or four weeks, they get their first external nutrition (from the cactus soil in the center of the pot which is slightly fertilized).
I left the gracilidelineata in their first soil mix for about a year (this was their first repotting: http://plant-whisperer.blogspot.de/2008/01/little-experiment-with-light.html). As far as I remember I did not give them any extra fertilizer, so they lived off the nutrients they found in the existing soil.
I repotted the one-year-old gracilis into a mix of cactus soil, quartz sand and volcanic soil, so the new mix had new fertilizer but a lower dosage than the first mix. But from this point on I started to give them fertilizer now and again (that means maybe twice or three times a year during the summer).
Another year later I repotted them again, this time into my now favorite soil: pumice. This contains no nutrients whatsoever, so regular doses of fertilizer are necessary. But again, regular means maybe four or five times a year during the summer (roughly once a month).
And this is how they still live today.
In my experience the most crucial point in growing Lithops at home (the way I do it, anyway) is to get them into real sunlight as soon as possible.
While they are germinating and the plastic cover is on the pot, it's still too early, though. They should not be put into the sun then because that will simply bake them in the moist air inside the pot.
But as soon as they are used to fresh air and when their roots have been covered so they can grow straight, they should move into the sun (carefully, though, you don't want to burn them).
My Lithops gracilidelineata showed a real change in size and strength once I relocated them to the windowsill into the sun.
Location: south facing window sill
Temperatures: summer - up to 35° Celsius or higher in the sun, winter - down to 3-4° Celsius
Fertilizer: orchid fertilizer with NPK 5:6:7, half the recommended dosage for orchids
First flower: after 5 1/2 years