The tree is large & 25 to 30 years old & is very healthy. I want to cut back a large limb on one side, because we keep bumping our heads on it when we use the path beside it. What is the best time of year to prune it, & should we get a professional to do it? (We live on the west mountain, near Hamilton)
How fortunate you are to have such a healthy Magnolia tree–from your description of ‘daisy type’ Magnolia tree, it’s possible that it is either a Magnolia stellata (Star Magnolia), Magnolia kobus or Magnolia x loebneri, a hybrid of the aforementioned magnolias. You mention that you “want to cut back a large limb on one side”. Typically, Star Magnolias are multi-stemmed shrubs (not what you describe); however, you may have the tree-form cultivar such as ‘Centennial’ whose flowers have 28-32 tepals (petal-like structures) which would resemble a daisy.
With regard to pruning back the limb, the best time to do so would be between late summer and late fall as the tree is going dormant. Since the limb is head-height, it should not be difficult for you to cut it back. The thickness of the limb will determine what tool should be used–for cutting finger-width twigs and branches, use a by-pass hand pruners (secateurs); for thicker branches, use loppers; if the limb is several inches thick, using a hand-held saw with a curved blade would be recommended. Make sure your tools are clean and sharp. [For more info, see: https://www.torontomastergardeners.ca/askagardener/pruner/].
In cutting back the limb, make sure that you cut back to a strong, healthy bud; the cut should slope away from the bud at a 45′ angle. When removing a large limb (from the trunk or main stem) with a saw, you will need to make three cuts to prevent the branch from tearing away from the trunk. The first cut should be made maybe halfway through the branch from the underside of the limb at least 12 inches (30 cm.) from the main branch. The second cut will be just outside the initial cut to remove most of the branch. The final cut then can be made near the trunk, usually at an angle to the trunk or main stem between the lower collar and upper ridge. [See: https://pubs.ext.vt.edu/430/430-456/430-456.html].
If you are successfully able to prune back the limb or remove it (if necessary), you will be able to avoid bumping your head when you walk by your lovely magnolia.