Only top section of apple tree in lead

[DuncanM]

I've got 3 minarette/ballerina apple trees in large-ish pots on my decking.

I've had 2 of them (red rocket and green rocket - names given to them when I bought them in Focus, I cannot find ANY information on those names however). These two trees have grown well and produced a decent crop for their size last year.

During the winter/spring I purchased another minarette tree, from T&M, a Lubera branded Malini Fresco. That year only the top 1/4 really had any growth on it, I thought it might have been due to the transplant so ignored it. However this year it is showing similar traits, albeit there is growth further down the trunk, it's just so far behind and absolutely tiny. It seems to be strange behaviour so I'm wondering if anyone could give any advice on it's condition please?

[boundtothesoil]

I don't grow minarette/ballerina apple trees, only normal bush trees on M26 and MM106 rootstocks, but I see what you mean about the one bought from Lubera. Others on this forum know much more about the specifics of these forms and techniques for encouraging the growth of lateral shoots. However, the tree looks healthy enough to me. At least you have signs of some leaf and shoot growth further down the trunk. These may develop during the growing season. At the moment the tree's energy is going into the top growth, and this will intensify if the flowers are pollinated and fruits begin to develop. One thing you could try is to remove the blossom on the tree this year. This may encourage more of the tree's resources to be diverted into growing lateral shoots further down the trunk. On the other hand it might also encourage the upper most shoots to grow faster.

[FB.]

Dwarf trees often don't have the powerful sapflows of vigorous rootstocks, so they can often only produce a few new shoots each year unless pruned quite hard during the winter - winter pruning invigorates and encourages branching in dwarf trees, but at the expense of delayed cropping.

Vigorous-rootstocked trees have so much sap being pumped up the tree in the spring that there's far more sap than can be vented-out by one or two shoots, with the result that multiple shoots can burst into growth. Vigorous rootstocks don't tend to need as much pruning to create branching.

[FB.]

Here's a picture of a MM111 apple tree which was left unpruned.
It naturally formed several side branches.
The central leader was removed the following winter, but the side branches were retained to form a spreading canopy with good wide (structurally strong) branch angles.
Retention of the leader was to improve the angle and position of the side branches: the leader was removed later.

.

[DuncanM]

So what do you suggest I do? Water it and feed it very regularly? (I do ensure they are watered well anyway) and leave it as it is, or prune the main(only) stem back next winter? If so, to what height?

[FB.]

So what do you suggest I do? Water it and feed it very regularly? (I do ensure they are watered well anyway) and leave it as it is, or prune the main(only) stem back next winter? If so, to what height?

Lots of watering and generous feeding (but beware over-feeding which will "scorch" the leaves). When grown in pots, dwarf rootstocks - with their relatively thicker bark - are much more resistant to root rots caused by over-watering than the more vigorous rootstocks.

Pruning next winter might be possible, but it is generally best to only cut into the youngest wood if invigoration is required. Cutting into two-year-old (or older) wood is less invigorating, although should still result in branching.
In my experience, any winter pruning tends to cause twin, competing leaders to develop; one of which will need training to a more horizontal position as it grows or removing during the next winter pruning.

The picture below (which I posted some months ago and for different reasons) gives an idea of how a competing leader occurs after heading cuts, and gives an idea of what to expect after using either heading cuts or thinning cuts: