Is too little heat bad for seed germination?

yes it is

Cool, moist soils are usually not conducive to good seed germination since there are frequently many different and virulent pathogens in the soil which can attack the seed. The germinating seed usually cannot grow fast enough to outgrow the effects of these pathogens and the seedling dies before it can emerge from the soil. This is why seed treatments are especially important when planting in these conditions.