Wet grass is heavy, lies flat and sticks to everything. A mower that cuts dry grass cleanly will tear wet blades, pack clippings under the deck and leave a patchy finish. In most cases the best thing is to wait a few hours.
Why is cutting wet grass a problem?
- Ragged cut. Wet blades bend away and tear. The torn tips turn brown and give fungal disease a way in.
- Clumping. Wet clippings stick together, clog the mower and drop in clumps that smother the grass below.
- Ruts and compaction. Soft ground takes wheel marks, and a heavy mower squashes it.
- Uneven finish. Grass flattened by rain stands back up later, so the lawn looks patchy the next day.
- Slipping. Wet slopes are slippery, and corded mowers add an electrical risk.
How long should you wait after rain or dew?
Until the blades are dry. After a light shower on a sunny, breezy day that can be two or three hours; after heavy rain the ground also needs to firm up. Dew usually clears by late morning, and evening cutting runs into the next dew. Quick test: walk across the lawn in dry shoes. If they get soaked or the grass sticks, wait.
The app has the same rule in its mowing details:
The mowing card in the calendar also gives a time window for each month, such as 09:00 to 18:00 in September, which keeps you clear of the wettest dew hours.
What if it will not stop raining?
In a wet British autumn you sometimes cannot wait for a dry day. If the grass is nearing one and a half times your usual height and the Met Office forecast shows more rain, cutting slightly damp is better than letting it get long.
- Raise the blades about 1 cm.
- Use a sharp blade. A blunt one tears even dry grass.
- Go slowly and overlap the passes so the mower is not overloaded.
- Empty the box often, or collect instead of mulching, so clippings do not clump.
- Avoid tight turns and soft, low spots, and skip slopes.
- Clean the deck straight away, before clippings dry on.
When it is raining or more than 2 mm fell in the last hour, What a Green Lawn raises the grass height chart for the current month by 1 cm and adds a note to cut a little higher to avoid clogging and tearing. For robot mowers it adds 0.5 cm.
What else helps?
Cut a little more often in the dry spells before a wet period, so there is less to take off when the rain comes. See what height to cut grass and how often to water your lawn, so a sprinkler does not leave the lawn wet when you want to cut.
What a Green Lawn shows the forecast, the month’s mowing window and the adjusted height in one place.