I have a red tailed boa, ball python, and dumerils boa. I want to start putting plants in their cages buti want to make sure it is done correctly. what kind of plants would be safe? strong enough? etc?

I don't know of any plants that are strong enough to withstand the strength and weight of ground-dwelling snakes like yours. (I use silk plants in my BP terrarium) "Michael's" and places like that have great looking fake plants.

We use live plants in our green tree python terrariums. (We keep them in pots so that they are easier to care for / replace and less likely to get uprooted by the snakes.) You could put the plants in pots and hide the pots in the soil and cover the edges with stones if you don't like to see them.
The plants we use are:
Philodendron scandens
Scindapsus pictus
Chamaedorea elegans
You need a good full-spectrum light bulb in the terrarium, but that's nice for looking at the snakes too.
Here's a pic of our 4 chondro terrariums:

Good luck and welcome to HC!

I agree with the uprooting thing. Definitely a big issue with snakes. It looks nice as well if you use some thick branches, drill some holes and hot-glue some fake leaves and flowers into them. They'll withstand the crawling over a lot longer than real plants. Also remember when adding plants that the water used for watering them will increase the humidity in the enclosure. Could be a good, could be a bad thing.

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Mike
"Never worry about numbers. Help one person at a time, and always start with the person nearest you." - Mother Teresa