As mentionned, growth and bud develeopement are severely slowed when the root zone goes below 50*, an electric fan heater works but can use 750-1500 watts on its own, an oil heater pays for itself many times over if you go this route, they retain heat so well, I cant stomach the electric bill so I dont go this route.
As a canadian grower I also am forced to grow in my unheated garage in winter by the wife, temps get below freezing even inside the garage, -20 C outside. What I do is use electric heat pads under the pots, I have them turn on when the lights turn off. I find a 20 watt pad will keep a 3 gallon pot plenty happy, the root zone will stay in the 60's.they sell them as rv water tank heater pads, or aquarium heater mats, all in various sizes and wattage ratings
Or they sell larger electric heated pet bed mat, electric battery blankets wraps if you wanted to place multiple plants on one large pad. Plenty of options to suit your grows needs. I really like the reptile terranium pads myself, only 10-20 watts per pad and only $5-$10 each and they have high qaulity water rated connections
On a side note Ive tried growing without any heating supplement in our 50 degree cold cellar, and my yield dropped literally 75%, plants just dont bulk or even grow when the roots are so cold