Often planted as a popular outdoor Christmas tree, Douglas firs grow steadily and can become quite large over time.
The best time to prune and shape them is in their youth, which means they have a limited window in which to be pruned. Here are the basics.
Prune when young. The best time to prune Douglas fir trees is when they are new and the branches can be easily reached.
Shape young Douglas fir trees. The most common shape is that of an upside-down ice cream cone with a slightly rounded base. This can be done using pruning or lopping shears. Some gardeners will trim the tree using hedging shears for a smoother all-around cut.
Leave older Douglas fir trees unpruned, except to remove dead growth or sparsely covered branches. Evergreens tend to "grow out," meaning their growth is on the ends of branches exposed to sunlight. Inside branches (and ones away from sunlight) tend to have few if any needles.
Do any pruning in winter, when the trees are fairly dormant. Evergreens never really "go to sleep," but like all plants, they have growing cycles, as evidenced by lighter green needles that appear at the end of branches. Pruning when the tree is dormant avoids the risk of pruning off new growth.
If you have a very large Douglas fir tree and want to cut it back or significantly prune it, first consult your local arborist or nursery.
Douglas firs can be quite prickly. Wear gardening gloves, a long-sleeved shirt and trousers when pruning, to minimise scratches.