Are you unable to plant them due to something being in the way of the planting site currently? (Such as a plant that needs removal first, or ongoing/planning construction?) If there is no obstacle to planting, we recommend they be planted as soon as possible. (There's no need to stop planting in winter, as long as the ground is workable, which means not frozen and not soggy. Plants won't get established during winter, but it's a safer way to overwinter them than keeping them in pots.) Bare-root trees, for example, have been successfully installed in mass city tree planting projects with minimal mortality even in the middle of winter. Once planted, as you would in summer, water them in and just keep an eye on watering needs throughout the rest of the season if the weather skews dry.

If you cannot plant in the location you want to grow the trees, then you have two options: planting them elsewhere temporarily, or keeping them in pots. The latter is the most risky option, because the roots will not be nearly as well insulated from temperature swings (and drying out often) as they would be if they were in the ground. Temporary planting is a method called "heeling-in," and it's simply planting a container-grown plant with the container still on and not removed. Then, in spring, the plant can be pulled up pot and all and relocated as needed. This takes advantage of having the surrounding soil insulate the root mass, though the potting mix inside the pot can still dry out periodically and need to be checked for watering needs. Desiccation is probably a bigger killer of containerized plants in winter than the cold outright, at least in our area where winters are not too severe.

If heeling-in isn't an option due to lack of a suitable space, then protect the container root balls as much as possible to reduce how often (and how drastically) they experience temperature swings, especially freezes. Freeze-thaw cycles could damage roots, and while the potting mix is frozen solid, it also won't be able to provide moisture to the roots, which can lead to leaf desiccation damage (for an evergreen plant) or potentially bud death and/or branch dieback for deciduous plants. Such damage might not manifest until spring. Adding mass around the roots will slow their change in temperature, so containers can be grouped together and surrounded by materials like mulch (loose in a pile or still bagged, whichever is easier for the situation at hand), soil, bales of straw, etc. Nurseries overwintering potted trees or shrubs may make a pile or berm of soil or wood chip mulch that they surround a group of trees with to insulate them above the ground. (Cinder blocks, bricks, wooden boards...a variety of materials can be used to contain the mulch/soil if needed, almost like a temporary raised bed.)

Bubble wrap and other thin materials won't insulate the roots much, and you'd want to avoid using anything impermeable like plastic to block wind, as it can also trap moisture and potentially lead to fungal issues later (or maybe interfere with rain or melting snow reaching the roots). Burlap, for example, can help reduce wind impacts on evergreens that need extra desiccation protection while establishing roots. There is no one correct method to use to overwinter potted plants...each gardener or nursery can do something different and have it work sufficiently well, so you might just need to experiment since it's unpredictable how many cold snaps we'll get any given winter, or how wet or dry it may be. The ideal, though, would be to overwinter the plants in the ground, preferable planted where they are intended to mature, so that they can also begin (albeit slowly at first) to grow roots into the surrounding soil to establish.

Containers that are hard to heel-in or wrap in some sort of insulating mass could be overwintered in an unheated garage or shed as one way to give them at least a little buffer from cold snaps or drying winds. You'd still need to check them periodically, when the pots are thawed enough, to see if they need watering. Watering is checked the same way it is during the growing season: feeling the soil a couple or so inches deep into the pot (or, if you're experienced with the wet and dry container weights, you can just pick up the pot). How deep to check for moisture really depends on the size of the container and how moisture-retentive the potting mix is. Once the mix becomes somewhat dry to the touch at that depth (an inch deep at a minimum, usually), then you'd water and let the excess drain out of the bottom drain holes. Make sure the containers can drain so that a cold snap doesn't create an ice dam blocking further drainage, which could keep the roots too waterlogged.

Miri