Posted: 26/04/2013 at 13:09
Welshonion is right about the size of the pots. The colour of the pots and even what they're made of will also contribute to their capacity to retain moisture.
The darker the colour, the more heat they will absorb, the quicker they will dry out. Terra cotta pots will dry out quicker than plastic ones because the terra cotta "breathes". Plastic doesn't. I prefer terra cotta because its capacity to "breathe" is, I think, healthier for the plant inside. The downside is portability. Terra cotta pots can get mighty heavy.
I hope you weren't fertilising your lavender and rosemary, Jessica, because it's the last thing they need. They thrive on controlled neglect in very very well drained soil.