Why does winter grass keep coming back?

Winter grass is persistent because of its life cycle, not because it’s hard to kill. It germinates in autumn, grows through winter, and produces seed heads in spring, often at a height below your mower blades. That seed falls into the lawn and waits for the next autumn.

So if you only deal with the plants you can see, you’re always a season behind. By the time winter grass is obvious, it’s either about to seed or already has. Next autumn the seed in the soil germinates, and the cycle repeats.

It also returns to the same places for a reason. Winter grass seedlings need bare soil and light, and they do best where the lawn is thin: worn paths, compacted areas, shade and damp spots. Some perennial types can also persist in some situations.

Breaking the cycle takes a season or two of doing three things: stop plants seeding (dig them out or catch clippings while seed heads are present), prevent germination in autumn with a pre-emergent that suits your grass, and thicken the lawn so there are fewer gaps.

How long until it’s under control?

Seed already in the soil doesn’t all germinate in one year, so expect to work at it for more than one season. Each year you stop plants seeding, there’s less seed waiting for next autumn, and each year the lawn gets thicker, there’s less room for seedlings. Most lawns improve noticeably within a couple of seasons of consistent prevention.

Are you bringing it in?

Seed can also arrive from outside your lawn: on mowers and edgers shared with other properties, in topsoil or topdressing, and from a neighbour’s lawn. If you use a contractor, ask them to clean the mower deck between jobs during spring, when winter grass is seeding.