How to care for your cactus
How to care for and propagate your cactus or other succulent plant
Assuming that your tortoises don't eat your cactus all at once, you may wish to grow them on, produce new growth and take cuttings, thus maintaining a continuous supply.
Prickly pears are very easy to grow.
Find a sunny location.
Plant in a gritty, free-draining soil.
Water well when dry in summer (Maybe once a week), keep dry in winter.
In summer they can be fed with any fertiliser suitable for tomato plants.
To propagate, just twist - or cut - off a pad. Allow to dry (callus over) for a few days. Then plant in slightly moist (or even dry) compost. Place out of direct sun, but in good light, in a warm place.
Leave for 2-3 weeks, then water. (By this time the cutting will have produced roots)
Move back into full sun. That's it!