Answer: The answer really depends upon the type of cactus you're growing. If they're upright and narrow in growth habit you can plant them about 6" apart. If they are short and wide, give them 8-10". This spacing should keep them happy for several years. It really won't matter that their roots grow together. You can separate them easily when it's time to repot. Simply remove them from the container and pop them into a basin or bowl of water. The water will help the roots float freely and you can separate the plants by gently swishing each around in the water.
Best wishes with your cacti!
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