How can I paint rubber composite planters?

I would begin with a good outdoor spray primer - Kilz makes a good one- and follow that with your paint color. Add a coat of protective finish to protect the new paint.

Home Depot has a paint for plastic that you can buy and spray paint or use some chalk paint.

Rustoleum 2X spray paint.

Hi Marsha, get a paint for plastics

Lightly sand the outside of the pot with fine-grit sandpaper and wipe the pot down again using a damp cloth. Put the pots on top of either a drop cloth or plastic sheeting to protect your surface. Spray the pot with your spray paint. Hold the can about 8-10 inches away from the pot and give it a light spray.