Can I use dry ice to provide CO2 for my plants?

Can I use dry ice to provide CO2 for my plants?
You can do this, but it is extremely difficult to regulate the sublimation of CO2 in an easy way. The cost of replacing the co2 every few days will rapidly mount up as it does disappear quickly once outside a freezer, and pretty quickly even inside a freezer.

Plus too much CO2 will kill your plants. It's hard to control the sublimation rate of dry ice, so you have no way of regulating the atmospheric content.

In short - don’t bother! If you really want co2 enrichment then buy a bottle and a regulator.