Some info on other Calandrinia germination here:
https://onrockgarden.com/index.php/germination-guide/germination-guideCalandrinia grandiflora A
Sow @ 20°C. Seed germinates within 3 months
Calandrinia sp. K *
N Sow directly in the garden. Sow at 10°C. * resents disturbance, perhaps fall planting
Calandrinia umbellata A
Sow @ 20°C. Seed germinates within 3 months
GERMINATION CODES ONTARIO ROCK GARDEN & HARDY PLANT SOCIETY
WHAT OUR TEMPERATURE DESIGNATIONS MEAN
4°C Either place seeds outdoors to be exposed to a wide range of winter temperatures including freezing or put them in a refrigerator (not a deep freezer).
10°C Either place seeds outdoors in spring or fall or choose a very cool indoor location.
20°C Either place seeds in a sheltered outdoor location in mid to late spring or grow at room temperature.
SYMBOLS
*This species needs special care as described.
? We have no information on the germination of this species. We sometimes provide an educated guess about which approach you should try. Let us know what is successful.!Sow immediately. The viability of these seeds is short or the species propagates best with fresh seed. Stored seed might be coaxed into germination with temperature cycling and patience.
LETTERS
A Sow @ 20°C. Seed germinates within 3 months.
B Sow @ 20°C. If seed does not germinate within 3 months, try 4°C for 1-2 months, then20°C again.
C Sow @ 20°C for 3 months, then place @ 4°C for 3 months.DUse repeated cycles of 20°C, then 4°C for 3 months each. Germination is very prolonged.
E Sow @ 20°C for 6 weeks, then place @ 4°C for 6 weeks, then slowly raise temperature to 10°C for 6 weeks. If there is no germination, repeat the cycle.
F Sow @ 4°C.GSow @ 4°C for 3 months, then place @ 20°C for 3 months.
H Use repeated cycles of 4°C, then 20°C for 3 months each. Germination is very prolonged.
J Sow @ 4°C for 3 weeks, then place @ 20°C.
K Sow @ 10°C.
L Expose to fluctuating outdoor winter temperatures including freezing for 3 months. Gradually increase light and temperature in spring.
M Store seed in moist medium @ 4°C for 3 months, then @ 20°C until radicle appears. Repeat cycle until leaf appears.
N Sow directly in garden.
NUMBERS
1 Resents transplanting.
2 Requires darkness.
3 Requires light or the small seeds should be surface sown.
4 Germination is improved by using GA3.
5 Germination is successful only when GA3 is used.
6 Requires scarification. Nick or rub between sheets of sandpaper.
7 Requires soaking. Place in warm water until seeds swell, usually 24-48 hours. Discard floaters and water used for soaking.
8 Pulpy coat inhibits germination. Remove by soaking and rinsing in clean water daily for 7 days. Discard water.
9 At one time, we advised "Tails may inhibit germination. Remove them." The advice applied primarily to pulsatillas and clematises. Our most recent data indicates that leaving the tails on has no effect on germination
