Most London garden centers will probably tell you to leave fibre pots and balled & burlapped root balls on when you plant. They may tell you to take off the lip and the bottom of fibre pots, but that’s generally all.
We used to tell people that as well, until my son started studying horticulture in great detail and learned that the world’s foremost tree experts suggest the opposite.
Those who have spent a lot of time observing what happens over time when the pots or burlap are left on agree you should take them right off, or at least remove the majority of them.
(The one time I do still leave them on is when the trees have been freshly dug from the field. In that case, it’s worth it to keep the container on in order to keep the root ball intact.)
Fiber pots and burlap are supposed to quickly break down in the soil, and they do if they are kept at the right moisture level and if you have the right microorganisms to break them down. If they dry out, or if the microbes aren’t there, they can take many years to disintegrate.
During the years they remain in the soil, they create a soil texture interface that may not let water pass easily, as does anything that is buried in the soil if it is a different texture than the soil. Sometimes this can lead to flooding in the pot and sometimes it can lead to insufficient water.
Also, roots might not make their way through the pot. Sometimes they just circle around inside the pot, making an unstable, unhealthy tree that eventually dies. Trees have died and been dug up decades after they were planted with the pot or burlap still intact. Or sometimes the burlap will decay, but the string will strangle the trunk.
Burlap is often treated with copper sulfate or other synthetics because it stays intact longer and keeps a tight root ball. It can last a long time in the soil. The string that ties it together is often synthetic, too.
Treated burlap is often hard to recognize. It can have a green color early in its life, but that fades. The way to tell is to burn a piece of it. If it melts and/or smokes, but doesn’t really catch fire, it’s synthetic.
Natural burlap and string are sometimes used instead, which is better. Traditionally, it has decayed within a few months under the right conditions, but it can last a long time if it’s dry, and they’re also finding ways to make it last longer. Good for the grower and the garden center, but not good once in the soil.
I don’t bother trying to figure out if it’s synthetic or not. I just take it off.
At the very least, take the string off and the top part of the burlap. If you fold it over, it takes longer to break down, so cut it off instead.
Wire baskets are used with big b&b plants to make them easier to move. I often leave this on because it’s a pain to get off of big root balls and it does help to hold them together if they’re made of sandy soil.
Tree roots can often grow around the wire without being hurt, so it’s not as big of an issue, although wire is occasionally found to be the cause of poor health in trees when it damages the root from the inside out.
In that case, the tree may just never reach a healthy state and hence always be covered in plant-feeding insects and diseases. It’s impossible to figure out unless the tree is dug up and examined.
At the very least, I cut back the top 12”-18” of the basket. If you want to take off the whole thing, first cut off the bottom half, then lift the tree into the hold via the top half, and then take off that top half.