My mandevilla’s have lots of blossoms coming but the vines are now over reaching the trellis I put in the pots. Should I prune the ends to promote growth lower down in the plant or should I let the vines fall over by their weight and start to trail downwards?
What a lovely plant! As mandevilla flowers bloom on new growth, the time to prune the vine is in early spring, before the new growth emerges. Although cutting it back or pruning the ends of the vine won’t harm it, this would result in lots fewer blooms, as we are well into the growing season (late June).
One option might be to add more support, e.g., a taller or wider trellis, to support the plant, although the added height/width may make your planter look oddly out of balance. Your best option may be, as you suggest, to allow the vine to simply topple over a bit – this would add interest although the shape would not be as controlled as you might have intended it to be – but the profusion of flowers would be the stars.