When to prune what?
April to May
Shrubs - Barberry, Boxwood, Chokeberry, Dogwood, Forsythia, Lilac (after it blooms), Cone Shaped Hydrangea, Roses, Viburnum and Weigela.
Evergreens - Juniper and Yews
May to June
Trees - Birch, Maple, Black Walnut
Shrubs - Potentilla and Spirea (can be pruned at any time)
Evergreens - Arborbvitae
July to August
Shrubs - Mop head Hydrangea (be sure to prune after the blooms fade)
January (or middle of Winter season)
Trees - Ash, Honeylocust, Linden and Oak
FEbruary to March (Late Winter SEason)
Trees - Apple, Cherry, Flowering Crabapple, Hawthorn, Mountain Ash, Pear and Plum
Shrubs - Cotoneaster
For more information on pruning, click on this link: