When to Prune Trees and Shrubs in Northern Illinois

Pruning at the wrong time is rarely fatal, with one important exception in our region, but it regularly costs people a year of flowers. The rules are simpler than they look once you sort plants into a few groups.

The oak rule, which is not optional

Do not prune oaks between April and October in northern Illinois. Oak wilt is a fungal disease spread by sap feeding beetles that are drawn to fresh wounds. An infected red oak can die within a single season, and the fungus moves between trees through connected root systems, so one mistake can take out a group.

Prune oaks in the dormant season, roughly November through March. If a storm breaks an oak limb in July, paint the wound immediately with pruning sealer. This is the only situation where wound sealer is recommended, and it exists specifically to counter this disease.

Elms follow a similar logic with Dutch elm disease, so keep them to the dormant season too.

Spring bloomers: prune right after flowering

These set their flower buds during the previous summer, so the buds are already on the plant all winter. Cutting them back in late winter removes the coming spring's flowers entirely, which is the single most common pruning mistake we see.

• Lilac, forsythia, azalea, rhododendron and mock orange.
• Bigleaf hydrangea and oakleaf hydrangea, which bloom on old wood.
• Spring flowering crabapple and magnolia.
• Prune within a few weeks of the flowers fading, and stop by roughly the end of June.

Summer bloomers: prune in late winter

These flower on growth produced the same season, so cutting them back while dormant produces more flowers, not fewer.

• Panicle hydrangea and smooth hydrangea, including the common white mophead types.
• Rose of Sharon, butterfly bush, spirea and potentilla.
• Most roses, pruned as growth begins in early spring.
• Red twig dogwood, cut back hard to encourage the bright young stems that give winter color.

General tree pruning

Late winter, February into March, is ideal for most deciduous trees. The branch structure is visible without leaves, the tree is dormant so it is not losing stored energy, insect and disease pressure is at its lowest, and frozen ground limits damage from equipment. Maples and birches will bleed sap if cut in late winter, which looks dramatic but does not harm the tree.

Basic technique

• Cut just outside the branch collar, the slightly swollen ring where a branch meets the trunk, and never flush to the trunk.
• Remove no more than about a quarter of a tree's live canopy in one year.
• Take out dead, damaged, diseased, crossing and rubbing branches first. Often that is all that is needed.
• Skip wound sealer except on oaks and elms pruned outside the dormant season.
• Never top a tree. It produces weak, poorly attached regrowth and permanently damages structure.

Anytime pruning

Dead, broken or hazardous limbs come off whenever you find them, in any season, on any species except oaks in the risk window. Safety outranks the calendar.

We handle trimming and shrub pruning across the North Shore and know which of your plants can be cut when. Call or text 224-634-0673 or 224-200-8363.

Ruiz Landscaping serves Vernon Hills, Libertyville, Mundelein, Buffalo Grove, Lincolnshire, Long Grove and the rest of Vernon Hills's surrounding North Shore and Lake County communities.