На сайте MG есть расшифровка этих цифр. 18 означает, что зимой кактус часто укрыт снегом и легко выдерживает -23 град. С.
Temperature for optimum germination: night minimum to day maximum:
1. 60's to mid 70's F (approx 17 to low 20's C)
2. 60's to mid 80's F (approx 17 to upper 20's C)
3. 70's to mid 80's F (approx 20 to low 30's C)
4. 60's to near 105F (approx 17 to near 40 C)
5. 70's to near 100F (approx 20 to upper 30's C)
Time to plant seeds:
6. any time of year with proper temperatures and daylength (ca.13-14 hours); you can extend day length with artificial lights.
7. fall and winter are best time, avoid heat of summer, short day length (ca. 11 hours)
8. remove from closed humid atmosphere soon after germination (ca.3 days)
9. slow to germinate, scarification and stratification help, freeze and thaw both wet and dry. Don't keep wet, but alternate wet and dry with changing temperature. No luck? Save pot and try again next year.
10. closed humid atmosphere important, distilled water useful with tiny seeds.
11. rot easily, right after germination: not too wet, dry air and stronger light.
12. soak in warm (approx 80F, 27C) distilled water about 12 hours before planting the seeds; do not allow to dry between soaking and planting.
13. needs soil with basic pH when first transplanted (add limestone), especially in areas with acidic water.
Hardiness of strong seedlings or adults in good health and culture:
14.no frost at all, fatal, keep above approx 40F (approx 5C)
15. occasional light frost, above 28F (-2C)
16. frequent moderate frost, above approx 20F (-7C)
17. very frost hardy, above approx 10F (-12C)
18. often snow-covered, safe easily to -10F (-23C)