Using my old outdoor soil indoors.

Not a good idea. Mold and fungus spores will be in the soil. Bug eggs can be dormant waiting for the right time to hatch.

Look, indoor it must have the least possible contamination from outside. You gonna deal with setting of temperature, humidity, nutrients, adapt plant morphology etc. Having a soil that could bring you pest or pH variations is not advisable.

I would at least sterilize the soil with hydrogen peroxide... it's a terribly beneficial way of both getting rid of insects and possible fungus AND improving the soil so your new grow will be off to a great start. Good article on this and how to do it is here: https://mmiagriculture.com/blog/how-to-sterilize-soil-with-hydrogen-peroxide/ Good luck!

Don't do it.......new grow = new soil. The risk of pest, diseases and contamination is too great in re-used old soil. Compared to the overall cost of growing, trying to save a few bucks by using old, depleted soil is false economy.

After diving into the rhizosphere, it's probably clear that sowing seeds in old soil doesn't guarantee success. This brings us to an interesting comparison: soil versus mud. Earth consists of living matter and a rich collection of nutrients. These help the cannabis plants survive and thrive. However, mud contains much less nutrients, organic matter and beneficial microbes. Cannabis plants can never reach their full potential if they don't have access to all the necessary nutrients. Mud without nutrients leads to stunted plants with less vigor and smaller yields. Living soil contains all the minerals cannabis plants need. In addition, it contains microbial life. These life forms ensure that these important nutrients are released.

You sure can! I suggest re-amending it, though. You may need to add more aeration, as well, if you used perlite or rice hulls instead of pumice or lava rock. The best stuff i've found for re-amending soil is called Craft Blend, made by BuildASoil. It has everything the plants could possibly need and it's totally organic, too. You don't need much, just 2 cups per cubic foot of soil. If you're afraid of pests being brought in with the soil, get your hands on some organic pesticides that can be used as a soil drench. The Amazing Doctor Zymes, Mammoth CannControl, and JADAM Wetting Agent(which is really easy to make yourself) can all be used. It really is better to be safe than sorry. I hope this helps.

I think it's an unnecessary risk. you can bring some pests along with the substrate, which are very difficult to get rid of. but if you still decide to use it, you should steam the substrate in the microwave or in the oven to kill all possible bugs. I wish you a lot of luck