1 Answer

Try not to prune mature magnolia trees unless they really have outgrown their allotted space. Established trees need little pruning.
If planting a new magnolia, place it where it will have space to grow to its full size. Magnolia x soulangeana cultivars can reach 20ft, Magnolia lilliflora may reach 13ft and Magnolia stellata cultivars often reach 10ft.
Where size reduction is necessary, select a few of the tallest or widest-spreading branches to cut back, rather than trimming back all the branches into a lollipop shape. This preserves the graceful shape of the tree.
Avoid large cuts into old wood if possible, as many magnolias can be slow to heal, frequently not making new growth until the second season after pruning. Prune them now, in midsummer, so they have time to heal before winter.
The season after pruning, look out for strong vertical branches known as 'water shoots' on vigorous magnolia trees such as Magnolia x soulangeana.
If possible, rub out the buds of water shoots before they emerge. Otherwise, prune them out to stop them spoiling the shape of the tree. If they keep coming back, try removing one third to one half of the water shoots, tipping back the others to discourage vigour.