The main reason for not using straw in potting is that the straw sometimes will have bacteria that could grow and cause rot in your pots. It would hold moisture in the soil and it will break down and may add a nominal amount of organic matter to the soil, but it wouldn't aid drainage for more than a couple of days. The reason for using something like perlite or vermiculite is that they are basically sterile. Pots can get too wet very easily and the perlite will maintain some air in the soil so roots don't suffocate.

Pine bark will rob some nutrients from the soil as it breaks down, but it makes such beautiful mulch on garden beds. ANy pine mulch would work better for plants like roses and flowers that prefer a high acid content in the soil. If you are growing tomatoes and peppers in planters a little top mulch would be good to help keep them from drying out too much during the day.

Cheryl

Thanks Cheryl. I'm glad I asked before reaching for that straw. MsB

All plant material, including us, have bacteria that are going to digest them when they are no longer alive and when all the right conditions are present. Straw would not be a good addition to potting soil any more than any other raw vegetation would, the bacteria would go to work digesting that material and using Nitrogen the plants need in the process. If you need to add something to your compost you will use in containers the best material would be perlite or vermiculite, which are inert.