I want to say that when I was looking into using pond foam they recommend you letting it cure over night. This way you are able to cut into it and it will be totally dry. Or add more layers. They did the back first then a side the next day then the other side the next day. The other cool thing I saw was someone permanently put in one set of pots into the foam and then they pushed straws into the bottom of the pot so that when they foamed the plants were able to easily drain water. They then just pulled out the straws when it set up the next day.