Which sprouts are you talking about splitting? I wouldn't have more than one Rosemary and one basil plant in a single pot. If given enough light, they will grow to a decent size in one season. If you planned on having them for multiple seasons you would probably never be able to transplant them out of a pot if their roots are graphed together. So planting one per pot or killing off the weaker sprouts later on would probably be a good idea, at least for those two plants.

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A man should look for what is, and not for what he thinks should be.
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