Problem Solver: Winter Grass Poa Annua - Richgro
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Winter grass Poa annua


Winter grass is a small annual weed 5 to 30 cm tall, with flat blades folded along the vein, and boat-shaped tips that curl up at the end. Flower-heads are open, with greenish white florets. It germinates as the soil cools, from autumn throughout spring, matures quickly and seeds early. In Australia it is a common weed of gardens, lawns, pastures and disturbed areas, wherever bare ground and moisture are available.

It starts growing and continues to develop in your lawn during cooler weather as the turf grass stops growing. It can become invasive and give your lawn an uneven, coarse look, especially where the lawn suffers from compaction, drought, or excessive mowing. On top of that, it is difficult to remove – as it is a grass, just like your lawn, regular weed killers are not effective to control it. Mowing is also not a solution, because winter grass can flower below mowing height.



Having said that, there are a couple of ways to get rid of it.

Combining a few gardening techniques may well be all that is required, if you have just a few winter grass specimens in your lawn. Winter grass has shallow roots and you can remove it manually, if you do it early, before it flowers and seeds. For specific problem areas, fork out the worst patches in early autumn (adding soil to re-establish the level) and re-seed, or lay patches of new turf.

Winter grass will not survive if the soil is very acidic. Richgro Sulphate of Ammonia is a lawn food that lowers soil pH a little. Feed your turf regularly, but not excessively – if conditions become too acidic this might adversely affect your turf as well.

There are also herbicides that specifically target winter grass. They are safe to use on common lawn types such as buffalo, kikuyu and couch, but if your lawn is none of those, it is important you check the product label before you buy. Your best bet is to apply it in autumn, to knock down the emerging winter grass seedlings. A second application may be required, best before winter grass starts to flower and seed.

If the winter grass infestation in your lawn is significant, it may be worthwhile engaging a turf expert.


Richgro horticulturist

Birgit Daller is a horticulturist and garden designer, and the owner and creative head of Art of Green Landscapes & Design.