The new part of our lawn by our extension is pretty good as it’s just been seeded. However, the part by the old house is really bumpy. So how do we flatten it?

Check your bumpy lawn by dragging a long two-by-four on a rope and marking the holes to fill. If they’re under one-half inch deep, use a 50/50 mix of potting soil and sand. From one-half to one inch, use a 70/30 mix of sand to soil, and from one inch to three inches use 100% potting soil.

Let’s dig down into the subject of fixing bumpy lawns in greater detail, and discover how it got bumpy, how to flatten it – and whether you should use a roller to do this…

How Do You Flatten a Bumpy Lawn to Make It Smooth?

Most lawn bumpiness can be fixed by simply filling in the holes and valleys. However, if your lawn has some seriously large hills – taller than three inches – then you may need a more serious solution.

If you have small holes and swales in your lawn, experts say it’s much easier to build up the low spots, rather than trying to compress the high ones. Identifying swales and leveling them with a topsoil mix is an easy – but strenuous – DIY project. 

If your lawn has really large bumps – more like small hills – that you don’t want, you may need to remove the underlying soil.

To accomplish this, you’ll need to carefully cut and set aside the turf layer that’s growing on the hill. Then you’ll have to dig out the underlying hill of soil. Once the soil hill is gone, replace the grass layer.

Here’s a nice reference.

Why Is My Lawn All Bumpy?

Lawn bumps are caused by a variety of things. The number one reason you may have shallow trenches or swales is due to water runoff. If you live in a cold climate and have clay-rich soil, your lawn may be made lumpy by the clay soil heaving – freezing and thawing unevenly.

You may have needed to replace a water or sewer line during the winter and the work created an ugly trench plus the heavy equipment left deep tire ruts. Tree roots and old tree stumps can create hills in your lawn. 

You can create your own lawn lumpiness by mowing the same direction every time all summer. Or, other creatures can create lumps and holes. Worms make small holes but voles, moles, raccoons and your new puppy – soooo adorable – can make big ones. 

Lawns can get lumpy due to too much drainage or too little. The next time it rains, or during a sprinkler cycle, take a hard look at your lawn. Does a sprinkler head shoot into your lawn and cause a trench? Does water pool up in places – like under a downspout or a broken sprinkler head. 

If you have drainage problems, consider fixing the underlying problem before spending money on soil or sand to even out your lawn. You may need to water less. Or, if you live in a wet climate, consider adding French drains, rain barrels, downspout extensions, or “creek” beds to help with the excess water. 

Should I Roll My Bumpy Lawn?

Experts say that it’s very difficult to roll a lawn smooth. It’s much easier to smooth a bumpy lawn by building up the holes, divots, swales and shallow trenches.

Do Lawn Rollers Really Work?

The best application for lawn rolling is for sport pitches. For home lawns, most experts say that rolling doesn’t help. In fact, running a heavy roller over your lawn may result in soil compaction, which is much worse than a lumpy lawn. You may end up with a perfectly level – but dead – lawn.

When soil is compacted, it doesn’t drain like it should. It holds water. Also, heavy rollers destroy large and small air pockets in the soil of your lawn. Healthy soil needs creepy crawlies like worms, insects, protozoa, nematodes. And the creepy crawlies, in turn, need oxygen. 

How Do I Level My Lawn by Hand? (Without a Roller)

Check your lawn level with a long, flat tool. You can use a (straight) two-by-four, a long wooden dowel like a rake handle, or a long level. Check out the video linked at the bottom of this section for a great DIY tool.

When you’ve identified your low spots, mark them.

Even though your lawn lumpiness may be driving you crazy, be aware that it may take a while to completely level your lawn. You may have to go in stages. The reason is that if you dump too much soil or sand – anything greater than one-half inch – on your grass, you will smother it and it will die.

If your lawn valleys are deeper than one-half inch, then you have a choice: either build up your swales over some time – weeks or seasons – or plan on reseeding.

Next, make sure your grass is in an active growing phase. Spring and fall are generally good bets, but the timing depends on where you live. Your grass should not be dormant.

Then, prepare your lawn by mowing it gradually shorter over several weeks. Experts say that the best height is from one-half inch to one inch. If you haven’t dethatched and aerated lately, this is a good time to do that as well. 

Check your local weather report. Make sure you have a good long dry spell coming up. Your lawn should be dry. If your leveling sand or soil comes to you damp and clumpy, then spread it out and wait for it to dry. Raking out clumpy soil will make your job much, much harder.

Prepare your mix. Experts say that the deeper your swales, the greater the percentage of organics your mix should have. So, if your holes or valleys are no more than one-half inch deep, you can just use fine sand or a 50/50 mix of potting soil and sand.

If your holes are from one-half inch to one inch, use a 70/30 mix of sand to soil. If your holes are from one inch to three inches, use 100% potting soil. Using all sand for deeper holes can weigh down the grass shoots and the reflective nature of the sand can burn the grass. 

If you are not reseeding, test a small area first. Dump a small amount of mix and then level it out with a rake, shop broom or leveling tool. Your leveling mix should not completely cover the grass. Make sure you can see tops of at least 75% of the grass blades above the mix.

If you are reseeding, then fill in the trench or hole with a small amount of mix, then stomp it down with your shoes. Add more mix, stomp it down. Repeat until your two-by-four checks that you are level. Finally, lay down the seed.

Here’s a nice how-to video on lawn leveling.

Is It OK to Put Topsoil Over Grass? (To Level It)

Yes! Otherwise known as topdressing, putting topsoil over your lawn can enrich your soil. Experts recommend choosing a soil that best matches your native soil, or at least the soil of your lawn. Then, make sure you don’t apply too much. 

How much is too much? Try to topdress your lawn with no more than one-half of an inch of soil. If your lawn needs more than a half-inch, just wait a few weeks and then apply more.

Be sure to apply the topsoil during the active growing phase of your lawn, not when it’s dormant. To calculate how much topsoil you’ll need, here’s a rule of thumb: you’ll need between 1.3 and 1.5 yards of topsoil for every 1,000 square feet of lawn.

First, make sure you have a good weather window and your topsoil isn’t too wet. Raking topsoil into grass is hard work and large clumps make the job even harder. 

Gradually mow your lawn until it’s between one-half inch and one inch high. Mark out where your lawn has low spots and concentrate on them. 

Shovel the soil into the low areas, then spread it with a shop broom, the flat side of a rake or a leveling rake. Try to get all the soil down next to the roots of your grass.

Here’s a good reference for topdressing, including a chart for topsoil volumes.

Final Words

The method of dragging a long, straight two-by-four on a rope to find and mark the holes in your bumpy law is absolute genius, and I’ll definitely be using it on our older section of lawn here at home.

Then you just have to remember those ratios of potting soil and sand for filling the holes:

• Under one-half inch deep, use a 50/50 mix of potting soil and sand
• From one-half to one inch, use a 70/30 mix of sand to soil
• From one inch to three inches, use 100% potting soil

This is a great technique and I can’t wait to get started. 🙂