The answer to this can be deduced from the comments already, really, but you say 45 degree latitude, which I take to mean 45th parallel north rather than south, and a perennial plant. That means the amount of daylight at the time of the shortest day is just over eight hours, with presumably low temperatures during the day and even lower at night. Any perennial plant you start from seed now, unless its big enough to plant outdoors by autumn and is hardy enough to withstand winter temperatures, will need to be kept indoors. And indoors, there's even less light, so etiolation will occur, and an average heated house is not a great environment during winter for a perennial plant either; the plant will not grow properly,or may not make it at all.
If, though, you have a cool but not freezing greenhouse (lightly heated to prevent freezing in other words), and if the plant is still a seedling, some growlights for the darkest two or three months, you're in with a chance of having a reasonably viable perennial to plant outdoors next spring.