Can a Robot Weed Your Garden?

June 29th, 2021

   You might be familiar with the Roomba, that little robotic vacuum cleaner that automatically patrols indoor floors for dirt and dust bunnies.

   You’re probably not as familiar with the Tertill, a similar idea for the outdoors that Roomba’s co-inventor Joe Jones developed along with robotics engineer Rory Mackean.

   Tertill, pronounced like the hard-shelled animal, looks like a fat, squat, smoke detector on wheels that patrols the garden for weeds.

Tertill’s underside is equipped with a short string-trimmer line to chop weeds.

   It has a small weed whacker attached to its underbelly that cuts off weeds as it meanders through beds.

   It’s a clever idea… and one that Jones envisions not only as welcome relief for weed-plagued home gardeners but a step toward using robots to help grow the world’s food.

   Tertill has been available for a couple of years now. It offers some intriguing possibilities but also some shortcomings, as I found when I tried a Tertill in my home gardens this spring.

   First, the pluses from my trial.

   Tertill runs on a built-in rechargeable battery fueled by a solar panel on its back, which means no plugging in and no buying a steady supply of replacement batteries.

   It’s also sturdy and weather-proof, capable of bouncing around on uneven ground, getting doused by rain, and dealing with erratic temperature changes without breaking down.

   Tertill’s wheels also do some surface tilling as the unit moves around, giving a second measure of weed discouragement.

   You have to give Tertill a few points, too, for coolness. Gadget-lovers, tech fans, and curious visitors will be impressed to watch this little gizmo rolling around whacking weeds automatically. My grandkids especially liked watching “the robot” in action and pushing its start button to play the cute “charge” tune.

   Most important, though, Tertill really can keep weeds under control – in the right setting.

   The problem is that there are a lot of settings that aren’t right. And if you’re trying to use Tertill in one of those, figure on a marginal job at best.

   The drawbacks are understandable once you see how Tertill is designed.

   The No. 1 issue is that Tertill doesn’t really “know” the difference between a weed and a desirable plant. It’s designed to cut off any plant that’s roughly two inches or less in height.

   Right away, that means that any existing weed bigger than that has to be pulled or killed to give Tertill a fighting start.

   It also means: 1.) seedlings and other short “real” plants have to be protected, and 2.) any weed that’s able to grow beyond two inches before Tertill whacks it is safe.

   Jones and Franklin Robotics, the Massachusetts company making Tertill, addressed the first issue by offering two kinds of wire wickets that gardeners can push into the ground around their no-whack shorties. That protects the plants, but it also creates extra expense (wicket packs are $20) and the work of placing, moving, and/or removing the wickets.

   I found the weed-patrolling issue to be a tougher problem.

   I first tried Tertill in a front-foundation bed that’s a mix of shrubs, perennials, and at the time, daffodils.

   I didn’t have any short plants to protect there, but I did have to use two packs of wickets to keep Tertill from wandering off into the lawn and beyond. (The company stresses that Tertill should be used in confined situations for that reason.)

   I also ended up resorting to boards to block off a third-side potential escape, which wasn’t the most attractive of landscape features.

   The unit turned on easily and at first looked pretty promising as it roamed and whacked.

   However, it ran only for about 10 minutes before shutting down to recharge. For hours.

   That turned out to be the norm as the unit spent most of the time dormant, running at best for maybe an hour or so total all day.

   When it was running, Tertill did whack off the leaves of most new weeds… but it didn’t get them all.

   In some cases, Tertill passed right by weeds. In other cases, the unit passed over top of a weed without the string whacker activating. And in other cases, the unit whacked a weed down to a stub, only to have it regrow.

   Sometimes Tertill would return to re-whack a regrowing weed, but other times, it either was off somewhere else in the garden or sleeping, giving fast-growers like hairy bittercress, dandelions, and plantain a chance to reach that two-inch lifeline to safety.

   The good news is Tertill didn’t harm any of my “real” plants.

   The bad news is that after about three weeks, my bed was getting noticeably weedier and weedier.

After two weeks on patrol, my second test bed looked like this. Tertill had spent a lot of time keeping the right side clean while allowing weeds to take hold on the left side.

   Not only were some of the misses and re-growers taking hold, but Tertill wasn’t able to cut off weeds growing right next to the shrubs or ones growing next to and within the clusters of daffodil foliage.

   That traces to Tertill’s maneuverability, which requires at least eight inches of space (the company recommends a foot) to get through and between plants.

   That was a big reason why I couldn’t use Tertill in my vegetable garden. I plant that intensively, both as a way to maximize production and a way to naturally limit weeds.

   In general, I garden under the principle that if you plant so that desirable plants touch (or at least use mulch or groundcovers to cover any bare ground), there’s no room for weeds to elbow in.

   Tertill, on the other hand, depends on open space between plants to maneuver – apparently, the more the better.

   I found that in cases where I had only foot-wide openings, Tertill didn’t always go through, usually opting for more wide-open choices.

   Either way, both in my first and second test beds (another front-foundation bed), Tertill patrolled just one section over and over for days before finding an open path to another section.

   Between that and the hours of daily down time, weeds in the other section had precious time to grow to safety height. I ended up having to pull all of those.

   On three occasions, I found Tertill lying upside down and helpless – with its wheels sticking up like a dead beetle.

Tertill flipped over when trying to navigate even this slight mound around a new columnar boxwood.

   What happened was that the unit tipped over as it tried to go up the slightly elevated mounds where I had planted a pair of columnar boxwoods in my clay soil.

   The company says Tertill is only able to handle 10 percent grades, which isn’t much.

   That was another handicap in my case since the bulk of my yard is on a slope – or worse. So besides having a confined bed, you’ll also need a fairly level one. And you’ll need one that’s no bigger than 200 square feet, which is the size Franklin Robotics mentions as the maximum Tertill can handle before weeds “get away from it.”

   Just to be sure, I tried Tertill on a newly planted slope in my back yard that runs about 20 percent. It quickly tipped and rolled down to the bottom.

   To its credit, the mishap didn’t harm Tertill, but that was a bed where some weeding help would’ve really come in handy.

   So what’s the bottom line?

   I’d conclude that if you have a level and confined garden of less than 200 square feet and plant so that you have ample room between plants, Tertill will do a good job.

Tertill has no room to maneuver in a block-planted vegetable garden like mine. It’s more suited for a traditional garden with rows and open paths.

   A traditional vegetable garden with the plants laid out in rows or a landscape bed with bare space between shrubs and perennials (and few/no seedlings or short groundcover plants) would be examples.

   You’ll also have to be willing to invest $349 for the weeding help… and be reasonably sure it’s being used in an area where no one will walk away with it.

   I’m not sure how long Tertill will last, but I know that the battery isn’t replaceable.

   My Tertill didn’t get stuck in the mud (as some gardeners have found), but besides tipping over, it did get hung up in a few corners. Figure on monitoring it every few days in case it needs to be “rescued.”

   Maintenance-wise, you might need to replace the weed-whacker string every now and then (a few extras come in the original box). The string is only an inch long and doesn’t spin nearly as fast as a gas-powered, full-sized string trimmer, but it’s a fairly simple replacement job.