After a few weeks of rain or a missed mow, your lawn can get out of hand fast. That’s when many people start asking the same thing: can robot lawn mowers cut long grass ?
The short answer is yes, to a point. Most robot mowers are designed to maintain lawns little and often, so very tall or thick grass can still be a challenge. Wet patches, uneven growth, and dense weeds may slow them down or leave an untidy finish.
In this guide, you’ll learn how robot lawn mowers handle longer grass, why overgrown lawns are harder to cut, and the best way to prepare your garden for smoother, more reliable mowing.
Can Robot Mowers Cut Long Grass?
Yes, robot lawn mowers can cut long grass, but they work best when the grass is only slightly overgrown rather than completely out of control. Most models are designed for regular maintenance mowing, where they trim small amounts often to keep the lawn neat and healthy.
If your grass has grown longer after a wet spell, a holiday, or a few missed mowing sessions, a robot mower will usually still cope. Many modern models can handle grass around 8–15 cm (3–6 inches) tall , especially those with stronger motors, adjustable cutting heights, and better traction.
That said, very long or thick grass is harder work for any mower, including robotic ones. Instead of cutting long grass cleanly in one pass, the mower may:
- leave uneven patches,
- move more slowly,
- drain the battery faster,
- or get clogged underneath with damp clippings.
Wet UK weather can make this worse. Long grass tends to bend and clump together after rain, which makes it tougher for smaller robotic blades to cut neatly.
Why Long Grass Is Difficult for Robot Mowers
Robot lawn mowers are designed to maintain lawns regularly, not tackle heavy overgrowth in one session. When the grass gets too long, several small problems start to build up, and together they can affect cutting quality, battery life, and overall performance.
Small Blades Struggle with Thick Growth
One of the biggest issues is blade size. Most robot mowers use small razor-style blades rather than the large solid blades found on traditional petrol or electric mowers.
These smaller blades are excellent for frequent trimming, but they are less effective when faced with thick, tangled, or very tall grass. Instead of slicing cleanly, they may bend the grass over or miss patches completely .
Thick Grass Puts More Strain on the Mower
Long grass also creates more resistance underneath the mower deck. The motor has to work harder, which drains the battery faster and can slow the mower down noticeably .
During fast-growing periods in late spring and summer, especially after heavy rain, thick grass can quickly overwhelm a mower that is running on a light maintenance schedule.
Wet Grass Causes Clogs and Build-Up
Wet conditions make it even harder for robotic lawn mowers to cut tall grass.
Damp grass tends to clump together instead of falling away cleanly. These clippings can stick under the cutting deck, clog the blades, and leave messy piles across the lawn. In some cases, the mower may stop altogether because too much grass has built up underneath.
Long Clippings Don’t Break Down as Easily
Robot mowers do not collect grass in a bag. Instead, they mulch the clippings back into the lawn .
When the mower trims small amounts regularly, this works well. The tiny clippings break down quickly and can help feed the grass naturally.
But if the lawn is heavily overgrown, the mower creates much larger clippings. These thick clumps sit on top of the grass rather than disappearing into it. In damp weather, they can stay wet for days and take a long time to decompose.
Too many clippings left behind may:
- smother healthy grass,
- block sunlight and airflow,
- or leave yellow, soggy patches on the lawn.
Long Grass Can Affect Navigation
Long grass can hide dips, edges, sticks, toys, or rough patches in the garden. That makes navigation harder, particularly for older robot mowers or models with basic sensors. The mower may miss sections of grass, change direction too often, or get stuck in thicker areas.
Best Way to Prepare Long Grass Before Robot Mowing
If your lawn has become overgrown, the best way to cut long grass is to start with a standard mower first, then let the robot mower maintain the grass gradually over the next few cuts.
Here’s what to do:
Start with a Higher First Cut
If the grass is very long, it helps to reduce the height gradually before using a robot mower regularly. A quick first cut with a standard mower or strimmer usually gives much better results than sending the robot mower straight into thick growth.
A good rule is to avoid removing more than one-third of the grass height at once , which lawn experts often call the “one-third rule.”
For example:
- if your grass is around 12 cm tall, cut it down to about 8 cm first,
- then lower it again to 5–6 cm a few days later,
- before letting the robot mower maintain it at your normal height.
Trying to cut very tall grass too short in one go can stress the lawn, leave heavy clippings behind, and make the mower work much harder than necessary.
Mow When the Grass Is Dry
Dry grass is much easier for robot mowers to cut cleanly. Wet grass tends to bend, stick underneath the mower, and form clumps across the lawn. In the UK, that often means avoiding early mornings when there is still dew on the grass or waiting until after rain has properly cleared.
Clear Debris Before Mowing
Long grass can easily hide branches, toys, pinecones, stones, or uneven patches in the garden. Before sending the robot mower out, take a few minutes to clear obstacles from the lawn.
Raise the Cutting Height First
Most robot lawn mowers allow you to adjust the cutting height. If the lawn is overgrown, start with a higher setting for the first few mowing sessions.
Once the grass is back under control, you can gradually lower the cutting height to your preferred finish. This gives a neater result and reduces strain on the motor and blades.
Let the Robot Maintain the Lawn Afterwards
Once the grass is back to a manageable height, regular mowing is the key . Robot lawn mowers work best when they trim small amounts often rather than dealing with long grass every few weeks.
Running the mower consistently helps create fine clippings that break down quickly into the lawn instead of forming heavy piles on the surface.
Best Robot Mowers for Hands-Free Lawn Care
Once you have brought long grass back under control, a robot mower can help keep it that way with much less effort. The eufy Robot Lawn Mower E15 and E18 are both designed for regular, hands-free lawn care, so you can spend less time pushing a mower around and more time enjoying the garden.
Their biggest advantage is the wire-free setup . You do not need to lay boundary wires around the lawn or install an RTK station. Instead, both models use pure vision FSD technology , with high-precision cameras and AI-powered navigation to map your garden, plan efficient routes, and avoid common obstacles as they move.
That makes them a practical fit for many UK gardens, especially if your lawn is not a simple rectangle. Flower beds, paving, narrow edges, trees, toys, and garden furniture can all make mowing more fiddly. With eufy, you can easily manage mowing zones, set no-go areas , adjust schedules, and check progress through the app.
Both models also include Ride-on-Edge technology , which helps them mow closer to lawn borders. That means less manual trimming afterwards, especially around paths, patios, and garden edges.
The eufy Robot Lawn Mower E15 and E18 share the same core mowing features, including:
- 203 mm cutting width
- Adjustable 25–75 mm cutting height
- 18° maximum slope handling
- Quiet 56 dB operation
- IPX6 waterproof rating
- Rain and low-light detection, with automatic return to the charging station
- 4G-enabled GPS tracking and anti-theft alerts
So, the main difference is not how they mow. It is how much lawn they are built to cover.
The eufy Robot Lawn Mower E15 is designed for lawns up to 800 m² . It is a strong choice for small and medium UK gardens, including family lawns, compact back gardens, and narrower outdoor spaces where regular mowing can quickly become a weekend chore.
The eufy Robot Lawn Mower E18 offers the same smart mowing experience but covers lawns up to 1,200 m² . It is better suited to larger gardens, longer grass areas, or homes with more open lawn space to maintain.
Conclusion
So, can robot lawn mowers cut long grass? Yes, but they work best when the grass is only slightly overgrown. If your lawn has grown thick after rain, holidays, or missed mowing, trim it down first with a standard mower or strimmer. Once the grass is back to a manageable height, a robot mower can take over regular care and keep your lawn neat with less effort through the mowing season.
FAQs
What height can robot mowers cut?
Most standard robot mowers in the UK feature an adjustable cutting range between 20mm and 60mm , though many heavy-duty models can reach heights of up to 80mm or 100mm . This spectrum is great for keeping typical lawns neat, dense, and healthy throughout the year. You can easily adjust the deck height via a manual dial or your smartphone app to adapt to the changing seasons.
Should I mow long grass manually first?
Yes. If your grass has shot up past 8 to 10 centimetres, you should give it a preliminary trim with a traditional manual mower first. Trying to send a robot straight into an overgrown lawn will strain its compact motor, heavily clog the cutting deck, and rapidly dull the blades. Lowering it manually first gives your robot a manageable baseline to maintain.
Can robot mowers cut wet, long grass?
It is highly recommended to avoid this. While modern mowers can easily cope with a bit of light morning dew, combining long grass with wet weather is a recipe for trouble. Long, damp grass clumps together tightly, sticking to the underside of the machine and forcing the motor to overwork. The slippery conditions also drastically reduce wheel traction, risking unsightly track marks on soft soil.
How often should a robot mower cut grass?
During the peak spring and summer growing seasons, your robot mower should ideally run every single day or every two days. These machines thrive on a “little and often” approach. Frequent cutting ensures they only slice off microscopic tips of the grass, which prevents machine strain and creates a fine, invisible mulch that drops down to feed nutrients back into your soil.
