Can i use pesticide free dirt from the backyard to make substrate with?

[Triple Supreme 8]

If so, whats the best way to sterilize it?

[Bugmageddon 3]

I’m not an expert but Normally I would go for baking, or freezing 

[Allpet Roaches 120]

Freezing doesn't do much unless you live in the tropics where few creatures can survive a winter. You can dry substrate on a tray but this can take weeks or months to kill every pest. Isopod hunters can survive months unseen inside a silk tube in soil or among plant material. You could buy some substrate from a pet shop or a garden shop.

[Acro 23]

On 4/18/2020 at 4:22 PM, Triple Supreme said:

whats the best way to sterilize it?

Some people pour boiling water into the substrate.  You can also bake it . . . I believe 2 hours at 250 degrees, but be sure the substrate your baking is moist or it will burn, and set off all your fire alarms.  Whatever you choose to do, be careful with boiling water and with baking flammable stuff.  

Good Luck!