How about a thermostat for a line-voltage electric heater?

@mtvhike I do not want to wire anything. I want something off the shelf that can be plugged inline to a standard 125V US electrical appliance.

Most soil probes will monitor air temperature as well as soil temperature. Instead of putting the probe in the soil just hang it up. Mine sometimes get loose and just hangs in the air, it still works. It's just not monitoring what i want to know. I bought an IPOWER brand on Amazon.ca for $26 CAD.

@gardengems was that the iPower 40-108? That particular unit is a maximum of 8 amps (kind of underpowered for a heater application...). I might give it a try but I hope they have a unit that can handle more amperage.

Any device like that is going to generate a small amount of heat from its circuitry. You really don't want the temp sensor inside the device as it will probably read high.

A device call the STC-1000 would do what you want, but you would have to put it into your own box. This is a programmable device. Available in C or F. In the US, F is preferable. Several YouTube videos on how to make the box.

@westes Zone 9b California SF Bay I can honestly say I did not understand the power you needed or even exactly what you needed, but I think I do now. You don't want something hard wired. The unit you are trying to power is a plug in heater. How many amps do you need it to handle?

@gardengems 10 amps is sufficient, but why not get 15 amps, the full rating of a typical home 125V circuit? It's just not a big deal to handle such a current load.

How about this? Lux WIN100 Automatic Heating & Cooling 5-2 Day Programmable Outlet Thermostat, Compatible with Portable A/C, Fans, and Space Heaters https://www.amazon.com/dp/B000E7NYY8/ref=cm_sw_r_cp_apa_i_H.j6Db4MXBNTN

inkbird controllers

Bob, have you seen this one?

I use the one for 50 degrees and it works great.)

https://www.amazon.com/Inkbird-58-212%C2%B0F-Temperature-Controller-Thermostat/dp/B01MXXBX26/ref=sr_1_2?keywords=temperature+controlled+outlet+60+degree&qid=1581876219&sr=8-2

@Meyermike, can the Inkbird sense air temperature without the probe?

I have that model Inkbird. It does not sense air temp without the probe. As the other poster said, why not use the probe as an air temp sensor?

By the way, I used it to control a milkhouse heater and discovered, after a year of use, that the back of the unit where it plugs into an outlet was heat damaged: it was darkened and some of the plastic was disfigured. I now use it only for controlling the temp of seed starting mats because they draw a lot less power.

If you want a commercial grade look for Johnson Controllers. They are UL listed, rated for 15A continuous duty. I have one of their thermostats that needs wiring. In those days plugin types were very rare and not easy to find. Had it for nearly 25 years and still going strong. Very safe. I will not opt for the cheap inkbird style device for unattended use with higher power devices. I just do not trust those - no safety rating whatsoever. For a few amp circuits they should be OK. I have one of the inkbird branded device that I rigged up for sous-vide. But I do not use their internal power relays - instead I wired it to use an external solid state relay rated at 25A continuous duty mounted on a aluminum heatsink. Works like a champ. Probably not something that you are looking for but mentioned it because you need to very aware of the safety issues with cheap stuff.