Why is My Lawn Mower Spitting Out Grass?

Most modern lawn mowers offer dependable performance and require very little by way of maintenance. But occasionally issues arise that leave homeowners scratching their heads. I can think of one such issue that left me with a big ol’ question the first time I encountered it: why is my lawn mower spitting out grass?

Now, you might be saying “Hey! If a lawnmower doesn’t have a grass catcher it’s going to deposit the cut grass back onto the lawn. Duh!” But that’s not what I’m talking about. I’m talking about grass that comes spitting out from under the mower at weird angles and in various states (loose, clumped, etc) whether there is a grass catcher attached or not.

It took me a while to get to the bottom of this, but I was able to unearth numerous reasons why a lawn mower is spitting out grass. Below, I’ve compiled a list of those reasons to help you out if you ever encounter this problem.

8 Possible Reasons Why Your Lawn Mower is Spitting Out Grass

If your lawn mower starts spitting out grass for no apparent reason this list may help you track down the culprit.

1: The Grass is Too Wet – I’ll start off with a pretty obvious one. Mowing a wet lawn is seldom a good idea, especially if you want as little cleanup at the end of the process as possible. Will mowing wet grass ruin your lawn mower? No, but wet grass is going to clog things up under the mower deck, interfere with the ability of the mower blades to cut effectively and spit out clumps of grass that you’ll need to go back and either collect or break up and distribute. Those clumps may be spat out the back of the mower, or if things get really gnarly underneath, they may come spitting out the side. Cutting dry grass is a much better idea!

2: The Grass is Too Tall – Waiting until the grass is too tall to cut it is another way to produce grass spitting out from under your mower. Like wet grass clippings, cutting or mulching tall grass can clog things up under the deck and cause grass to come shooting out at weird angles. Typically, the amount of grass is pretty modest, and it doesn’t happen every time. But sometimes, if you wait until the grass is too tall to cut it, you may see grass spitting out the sides and front. Cutting long grass can also produce the aforementioned clumps.

3: The Wrong Type of Blade – Lift mower blades are designed to create suction that pulls (lifts) the grass up toward the blade to create a nice, clean cut. Lift blades are available in different designs that create different amounts of lift. But their effectiveness depends on having a motor that’s up to the task. If you have a blade that’s designed to create high lift, but your mower’s engine is not capable of spinning the blade fast enough to create that lift, it may cause a situation where the grass is being cut unevenly and some clippings are flying out the sides of the mower.

4: A Clogged Chute – If the grass on your lawn is long or wet it can lead to the discharge chute becoming clogged. Once this happens the grass you’ve cut will have nowhere to go and come spitting out in different directions. But this doesn’t just happen when mowing tall or wet grass. If the chute hasn’t been cleaned in a long time, regular dry grass clippings can build up inside too, like lint in a dryer vent, and cause the same spitting problem.

5: A Dirty Mower Deck – Many homeowners will go a full year without ever flipping their mower over to see what’s going on under the deck. When they finally do they’re often greeted by a thick carpet of grass clippings stuck to the underside leaving just enough room for the blade to spin. For the mower to operate properly the underside should be clean and smooth so that clippings have an unimpeded path to the chute. If the underside of the mower deck is clogged up some of those clippings won’t find the chute. Instead, they’ll come spitting out in all directions.

6: A Poorly Fitting Grass Catcher – If the grass catcher doesn’t fit properly clippings are not going to proceed into the catcher in an orderly manner. Some will make it into the catcher, but others will trail behind the mower, and still others will ricochet around under the mower and then come spitting out the sides and even the front. If the problem is just that the catcher was not attached properly, that’s pretty easy to fix. But if the catcher is broken or damaged it will need to be replaced.

7: Underinflated Tires – This is a problem that sometimes pops up with riding mowers. One tire will be underinflated or have a tiny puncture that is causing air to slowly leak out. The mower then becomes unbalanced with one side higher than the other and clippings begin flying out from under the elevated side. The rider then starts wondering: “Why is my lawn mower spitting out grass?” The difference in tire pressure does not have to be extreme. Just a few psi can cause the mower to ride unevenly and grass to come spitting out.

8: A Thatched Grass Catcher – We covered the issue of a poorly-fitting or improperly attached grass catcher. But the catcher can cause grass to spit out from under your mower for other reasons too. For instance, if the grass bag is thatched it can interfere with airflow. That can prevent the grass clippings from being carried into the bag. In which case, it may come spitting out the sides of your mower.

The Final Word

If your lawn mower is spitting out grass there has to be a logical reason for it. Use the above list to troubleshoot the situation and restore your mower to proper functionality.