Some plants - especially many hardy perennials - prefer to be planted/germinated in cool temperatures. For example, on the site for world plant seeds primula (as a new member, I may not post a link) , it says:
Sowing Advice
Primula seeds may be sown at any time onto a loam-based compost, barely cover so that around 50% are still visible. Best germination temperatures are between 10 and 15 degrees C. (e.g. a cool, northerly window sill) PLEASE NOTE: Temperatures exceeding 15 C can prevent germination, and above 20 C expect very little germination as most seeds will go dormant as a protective measure. Germination takes between 3 to 6 weeks, sometimes taking much longer.
A friend and I each planted Crocosmia 'Lucifer' bubs this year. I planted 30 outside after there was no danger of frost but the temperatures were about 10-15 during the day and 5 or so at night. My friend planted them in pots in a greenhouse where they were much warmer.
I got germination over 2 1/2 growths from every bulb. My friend got about 40% germination in th much warmer greenhouse.
Draw your own conclusion.
