could you stand the pots in the very large ones and pack under and around them, It would help insulate the roots from frost, then slowly repot the bays as they need it

The size didnt strike me as over large re the height Bays tree grow to, so you could mix the compost with Perlite / Vermiculite this would help with water retention and weight.

Im a horder and always have polystyrene packing in my greenhouse to use as insulation etc; if you can get hold of some it comes in very handy to pack at the bottom of pots so you dont need as much compost.

I also would expect a 65 cm planter to be just barely big enough for a bay tree. You can follow Maggy's suggestion, if weight is your concern, but you will still need at least 40 cm of compost on to to support the tree. Also, if the area gets occasional wind, you will want the weight to help keep them from tipping over.

i would actualy use bigger planters and save having to repot them . i nice little trick thow if you dont want to move them and the planters are cuttable . you can cut the base out of planters and they will be able to root as they want but still look like there in a pot .shouldnt you put a bit of old broken crockery,cklay pots at the bottem for drainage and to stop the siol pouring out the bottem ? x

Here in the desert we usually just use a screen over the hole, to allow maximum root depth. We've also found that any sudden change in soil texture will stop or slow the drainage, even a change from heavy soil to a coarse one.

I stopped using crocks and now just put a J cloth or a piece of weed suppressant across the bottom to stop insects getting in and it keep the holes free from compost. I do still stand my pots on feet to deter ants etc.

sounds good to me thanx