If it is warm in your basement they may need to be watered more than once a week. Check them more often and water if the soil is dry. If they are actively growing they will need more water. I have one upstairs that needs water every few days while the one downstairs that hasn't started new growth does okay with water just once a week.

I would hold the pots under water until bubbling stops to make sure they are completely saturated and that the soil isn't completely dried out and the water hasn't been just draining away rather than wetting the soil.

Lavender is difficult to grow indoors. Once you can put them outside they will fill out and grow really well. In terracotta pots they will need to be checked and watered more often than ones in the ground.

Sounds like a nice wedding centerpiece.

Thank you for the input. I pulled apart the roots of one of my problem plants and it was much more dry than I would have suspected based on the top soil. In short, I think you are correct!

The plants are pretty active and even sprouting flower buds, so the growth may be the culprit. I transplanted from 2 1/2 inch pots about a month ago and the roots had already begun to fill in the full 6" pot.

Thanks, again.