Sometimes it is beneficial to start the seed indoors when it's cold outside. A common mistake is to place the seed on a cold windowsill and walk away. It's one of the driest and draftiest locations usually. Seeds like moisture and warmth to start. Usually moisture like a wet sponge (not drippy) and temperature around 70 degrees. Some like 80 (i.e. okra). Some like 50 (i.e. radishes). A meat thermometer can help you locate a nice spot. If you are like me, and really don't have that spot in your house, what do you do? Many places will sell heat mats and lamps. These work. The plants that only want to germinate in warm weather will likely only thrive in warm weather. The only down side is now you are stuck investing electricity in your seedlings.
If, however, you have some seedlings that need it a bit warmer, but your house is just under germination conditions, consider a moist paper towel in a plastic bag in your jacket pocket. If during winter you are constantly wearing a jacket (because it's too cold) then you are constantly making that jacket just about the right temp for you. Most people are comfortable around 70 degrees, which is the perfect germination temperature! Measure the pocket's temp if you are not sure. Check your seedlings daily for germination, and when their little tails appear, plant them in a warm spot.
I did this with dragonfruit seed and got a very high germination rate.
Peppers like 80 to 85 degrees.
This year I am using a old chicken incubator.
It is holding around 84. I will put seed in paper towel and inside a zip lock bag. Need to watch for mold.
I will post results.