Cold room not attached to house.

Having problems with a cold room not attached to house its gets about 50 % the coldest its not on foundation..Concrete floor thinking of getting one of those radiator heaters and maybe put some plywood and tarps on the ground also or something in that combination any suggestions week 2 going into 3

Foam insulation on the floor might help with plywood on top of the foam for durability. Radiator type heaters give nice even heat. If you pair that with an Inkbird or similar temp controller, you should be good to go.

Imo anything thats not insulation/ed like plywood or tarps will just acclimate to temp of floor. Insulation board is cheaper than plywood . Sounds like a heater is a must

An issue to think about with a cold room is how you intend to bring in CO2 from outside to replace the CO2 used by your plants without dropping the temp of your room to lower than ideal. A tent inside your room would allow you to warm your room air before it goes into the tent. A CO2 burner might be another option to consider. It would help keep your room warm, you could seal your room to the outside, and have whatever level of CO2 you want without drawing in cold air.