Why Your Lawn Has Ugly Stripes (And It Is Not the Grass)
Have you ever finished mowing and noticed that your lawn has wavy lines? Some strips look shorter than others. Some patches look scalped down to the dirt. The edges of the deck leave ridges. You think it is the mower. You think you need a new one.
You probably just need to level your deck. An unlevel mower deck cuts grass at different heights on the left and right sides. It also affects the front-to-back pitch, which changes how the blades meet the grass. The result is a lawn that looks like a bad haircut. Here is how to fix it with basic tools in about 20 minutes.
Tools You Need
- Tape measure
- Socket wrench set or adjustable wrench
- Air pressure gauge (or tire inflator with gauge)
- Level surface (garage floor, driveway, or flat pavement)
- Scrap piece of wood or spacer blocks (optional)
- Your mower’s manual
Step 1: Check Tire Pressure First
Before you touch a single adjustment on the deck, check your tire pressure. A low tire on one side tilts the entire mower. The deck could be perfectly level but the mower is leaning because a tire is 5 PSI low. This is the most common cause of an uneven cut, and it takes 2 minutes to fix.
Check all four tires with a pressure gauge. The recommended PSI is printed on the tire sidewall (usually 10 to 14 PSI for rear tires, 14 to 22 PSI for front tires). Inflate any low tires to match the others. Use a gauge. Do not eyeball it. A tire that looks fine can be 5 PSI low.
Seasonal Lawn Sale Ends Soon
Don't wait until prices go back up. Save on lawn equipment, watering tools, weed control, and gardening essentials today.
Step 2: Park on a Level Surface
Move the mower to the flattest surface you have. A garage floor is ideal. A driveway works. The measurement you are about to take assumes the mower frame is level. If the mower is on a slope, your deck measurements will be wrong.
Set the parking brake. Lower the deck to a middle cutting height (about 3 inches). This is where you will take your measurements.
Step 3: Measure Side-to-Side Level
This is the most important adjustment. A deck that is higher on one side cuts grass at different heights. Your lawn will look striped with alternating tall and short rows.
Rotate the blades so the blade tips point left and right (parallel to the axle). Measure from the ground to the tip of the blade on the left side. Measure from the ground to the tip of the blade on the right side. The measurements should be identical or within 1/8 inch. If one side is higher than the other, you need to adjust the side-to-side level.
On most mowers, the side-to-side adjustment is a threaded rod or bolt on one side of the deck linkage. Loosen the jam nut. Turn the adjuster to raise or lower that side of the deck. Remeasure. Adjust again. Tighten the jam nut when both sides match. Your manual will show the exact location of the adjuster for your model.
Step 4: Measure Front-to-Back Pitch
The front of the deck should be slightly lower than the back. This is called “pitch.” The reason: the blade cuts grass as it rotates forward. If the front of the deck is lower, the blade tip meets the grass at the front, cuts it once, and then the grass passes under the raised back of the deck. If the deck is level or tilted backward, the blade cuts the grass multiple times, which wastes power and creates uneven cuts.
Rotate the blades so they point forward and backward (perpendicular to the axle). Measure from the ground to the front blade tip. Measure from the ground to the rear blade tip. The front should be 1/8 to 1/4 inch lower than the rear. If not, adjust the front-to-back pitch.
On most mowers, the front-to-back adjustment is on the deck lift linkage. Some models have a separate adjuster nut. Others require adjusting the deck hanger bolts. Check your manual. Make small adjustments and remeasure until the front is 1/8 to 1/4 inch lower.
Step 5: Clean the Deck (Important!)
A level deck with caked-on grass underneath still cuts unevenly. The grass buildup changes the airflow. While you have the mower on a flat surface and the deck raised, take 5 minutes to scrape the underside of the deck clean. Use a putty knife or a deck wash port if your mower has one. A clean deck plus correct leveling equals the best cut your mower can produce.
Step 6: Test Mow and Fine-Tune
Mow a test strip on a flat section of your lawn. Look at the cut. Is it even side to side? No stripes? No scalping? If the cut looks good, you are done. If not, make small adjustments and test again. Deck leveling is sometimes trial and error. The tape measure gets you close. The actual cut tells you when it is right.
Signs Your Deck Needs Leveling
- Alternating tall and short strips in the lawn
- One side of the deck leaving a ridge of uncut grass
- Scalping (cutting down to dirt) on one side only
- Uneven grass height when mowing at the same deck setting
- After hitting a solid object (stump, rock) that may have knocked the deck out of alignment
Seasonal Lawn Sale Ends Soon
Don't wait until prices go back up. Save on lawn equipment, watering tools, weed control, and gardening essentials today.
Disclosure: This article contains affiliate links. As an Amazon Associate, I earn from qualifying purchases. This means if you click a link and buy something, I may receive a small commission at no extra cost to you. I only recommend products I have personally tested or thoroughly researched. Thank you for supporting GrassBlogger.
Shop How to Adjust Your Mower Deck for a Level Cut on Amazon
