It depends on where they're going. Sending soil is a no-no beween the European countries and us, so I have to remove soil, wrap them in damp moss, find something stiff that isn't too heavy and wrap everything in plastic before finding a bolstered envelope and sending as letter. That's the quickest and easiest way. Inside Norway I just pot them up, wrap them in newspapers and put them inside one of the Mail Service's cardboard boxes. All pre-payed for up to a certain weight.
Hi, i always send my plants like this. Plastic water bottle, cut a slit down the centre, leave screw top on. Then wrap your plant/s in a little plastic,use sellotape to seal the slit put on addess label large enough for stamps to fit, then sellotape all round 2/3 times very secure always arrive safely plants in healthy condition. Hope this helps. Fuschia. :-D PS large or small bottle which ever one suits the amount of plants. :-D