Prune back overgrown shrubs in the fall

Plants have been putting on a lot of growth this summer and the ones you pruned in June and/or July may need to be touched up again. I have been seeing more late-season growth on shrubs than in years past.

Keep aware of spring flowering shrubs like fragrant viburnum and lilac that have set flower buds for next year — over pruning now will remove next year's flower display.

• Be sure to keep checking the oil and cleaning out the air filter on your lawn mower on a regular basis. The engine can be ruined by letting it run out of oil. The dust raised when mowing over dry leaves later in fall can clog up the air filter, which will impair performance of the engine.

It is a good idea to sharpen your mower blades after about every eight hours of mowing.

• Look for woody plant weeds like mulberries, buckthorn and box elders that grow up among shrubs and in hedges. These weeds tend to be hard to spot when they are young. They can also grow alongside and into fences, making them difficult to remove. Try treating the stumps — with an herbicide like Roundup that contains glyphosate — immediately after cutting to kill the root system and save you the trouble of digging out the stump.

• Crab grass may be evident in your lawn now, especially if it has been neglected or in areas along driveways or walks that are compacted from foot and vehicle traffic. This annual weedy grass has a wide leaf blade that is light green and seeds readily in the fall.

Pull it out by hand, if that is feasible, to prevent seed formation — it is difficult to mow it low enough to remove any seed. There are herbicides that will control crab grass, but they will not be as effective after the crab grass has set seed. These herbicides are most effective when the plants are young and actively growing but tend to be difficult to identify unless you are looking closely.

Make note of bad areas in your lawn and apply a pre-emergent herbicide (one that prevents weed seeds from germinating) in early spring before lilacs flower.

• Tim Johnson is director of horticulture at Chicago Botanic Garden,

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