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Annual bluegrass – it’s driving me mad

I’m surprised at myself. I didn’t think I was that guy obsessed about the lawn.
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I’m surprised at myself. I didn’t think I was that guy obsessed about the lawn. I’ll admit I take a certain not-so-quiet pleasure that my lawn is always darker than my neighbour’s – obvious where the two properties meet in the front yard regardless of how much he fertilizes in an attempt to catch up (my secret is that I grew my lawn from seed, choosing the darkest available cultivar of Kentucky bluegrass (Poa pratensis [‘Quantum Leap’]). But I’m relaxed about the dandelions and other weeds – there’s always some and I’ll get to them eventually. I let the patches that died over winter fill in on their own. And I fertilize when I have time, not particularly on any schedule. But the bright, light green patches of annual bluegrass (Poa annua) are driving me mad.

Annual bluegrass is a common lawn weed. And because it’s a grassy weed, the usual lawn broadleaf weed killer (a cocktail of 2,4-D + mecoprop + dicamba) isn’t a solution to this problem. Annual bluegrass a short, shallow-rooted grass that tolerates compacted soil. Tawny-coloured seed heads can form well below the mowing height allowing it to produce seed unchecked. Desired turfgrass species, on the other hand, rarely have a chance to produce seed since seed heads are constantly mown off. Viable seed is produced in just days after pollination and individual plants can produce more than 100 seeds in a season. This allows it to continue to spread much of the season and out compete the regular turf grass species where the lawn has become weak due to winter die back, drought, insect infestation and other challenges. Lawn maintenance equipment (mower, string trimmer, aerator) and your shoe bottoms are the main culprits in spreading this scourge.

A healthy lush lawn is your best defense against annual bluegrass invasions. But that can be difficult to achieve here on the prairies where we face temperature and moisture extremes. Here are few strategies to prevent and control annual bluegrass incursions.

• Water your lawn deeply (one inch of water, increase to 1.5 inches at the height of summer heat) and infrequently (once per week) to promote deep rooting by the desired turf grass species. Shallow, frequent watering keeps the soil surface moist which is ideal for annual bluegrass establishment.

• Pull out annual bluegrass patches by hand as soon as they appear. It has a shallow root system and should come out easily. Reseed with desired turf grass species. Because dormant seed can lay dormant for two or more years, revisit old patches often and remove new annual bluegrass seedling.

• Deal with winter-killed or weak areas immediately by reseeding with desired turf grass species.

• Keep you lawn equipment clean. If renting (e.g. aerator, dethatcher), wash it thoroughly before using.

• Raise the mowing height to reduce stress on turf grass and improve its ability to compete. Close-cropped lawns tend to have shallower root systems and are more prone to stress.

• Mow often during periods of rapid growth.

• Remove lawn clippings to prevent spread of annual bluegrass seed.

• Aerate lawns in mid-summer, when annual bluegrass seed is less likely to germinate.

• Skip fall fertilization to avoid stimulating annual bluegrass growth.

While there are registered pre-emergent herbicides (prevents seed germination, but does not control established weeds) for annual bluegrass control in established lawns, they are only available to commercial applicators.

— This column is provided courtesy of the Saskatchewan Perennial Society (;; Check out our Bulletin Board or Calendar for upcoming garden information sessions, workshops, tours and other events: Join us on our first garden tour, June 12. GardenLine is back for the season to help solve your gardening glitches, free. Phone 306-966-5865 or email