You shouldn't need to cover with plastic. These plants like full sun - I'd imagine planting them to the west will mean not very much sun, so try to put them where they'll get maximum sun exposure. Bear in mind that you need to leave a distance of about six feet between the base of the tree for your planting hole - even there, you might find too much root material to plant successfully.

Wendy
1. Do not cover the pots and plant out as soon as the shoot shows.
2. They do not need enriched soil, at least, not particularly.
Bamboo says to grow in full sun. We had ours in a south facing position but I know a shady garden in Aberdeen where the plant has become invasive. The tuber can be planted in shade but as this is a herbaceous climber the vines will quickly work their way round to the sunny side of the tree.
If Tropaeolum speciosum likes your garden then it can become a thug. It mulitiplies by producing more tiny tubers and by seed which explode over the garden. I know a number of Scottish gardens where it rampages over all the shrubs and this is the reason that we removed ours. Essex has a different climate and this might not be true for you. Regardless, it is a most attractive plant and I hope that it does well for you.

Hi Wendy, whatever you do make sure the roots are well shaded, the top growth likes sun and keep the roots well watered...:>)