Cut the grass
Electric lawnmowers
Oh great! A Paul Kelly song to illustrate the topic du jour! Before we do anything else, let’s check out what Australia’s greatest living songwriter1 has to say about mowing...
OK, I’m sorry. That was truly appalling. Forgive me.
Mowing: not just lawns and small engines
If you managed to make it through more than a couple of frames of the video clip, you’ll have seen that mowing isn’t just something that occurs in backyard lawns. The scythe and haystack of medieval farming has been replaced by enormous tractors with mowers, mechanical rakes, and automated baling machines to make hay or silage.2
For the remainder of this post we’ll concentrate on lawn mowing, but longer-term, we’ll cycle back to the question of greening this kind of large-scale agricultural machinery. Suffice to say that there are real technical challenges.
Lawn mowers: the present landscape
So, let’s look at lawns. While lawns are environmentally questionable for many reasons beyond the emissions of lawnmowers, they are also a heck of a place for kids (and adults) to play. So, again, they’re not going away entirely any time soon.
In theory, you don’t need any kind of engine at all to mow a lawn. Human-powered “reel” mowers have been around for well over a century. With certain types of grass, climate conditions, and a lot of time on your hands, they actually work rather well:
They’ve never been particularly popular in Australia. I’m not entirely sure, but I believe it’s in part because the grass species used here are tougher to cut than the most popular types in the USA. And who has the time to mow your lawn multiple times a week except greenkeepers at golf courses (who usually use a powered version of the reel mower to mow greens)?
The majority of domestic mowers use a different design, the rotary mower. As most people would know, a rotary mower features sharpened blades rotating at high speed - requiring far more energy than a person could realistically provide. As well as slicing the grass, the rotary blades act as a upwards fan, lifting the grass blades vertically to help get a more even cut. While not quite as neat as the regular use of a reel mower, the rotary mower is capable of cutting much longer, tougher grass.
Rotary mowers are available in three basic configurations. The smallest and cheapest is of course the push mowers made famous by Mervyn Victor Richardson and the Victa brand. Smaller push mowers rely on the operator to move them about; some larger models have power assistance. The largest hand-held petrol-engined mowers have engines producing about 3.5 kW - considerably less than the chainsaws discussed on a previous blog post.
There are then two basic types of ride-on rotary mower; the first is the “lawn tractor” - as the name suggests that resemble a miniature tractor, with conventional steering from the front wheels.
Acabashi, CC BY-SA 4.0 via Wikimedia Commons
The most elaborate small mowers available are “zero turn” ride-on mowers. These are steered by braking one of the rear wheels, with the front wheels mounted on a large castor, giving them the ability to perform much tighter turns:
These mowers also often have wider cutting decks with multiple rotary discs, making them much faster for mowing large areas.
Combustion-engined ride-on mowers are typically powered with small four-stroke petrol engines. The very largest of these, for commercial use on very large properties, can have up to 25 kW (35 hp) engines, well beyond the scope of California’s small engine ban. Interestingly, there seems to be relatively little use of diesel even in these larger mowers.
Electric options - technically viable, but financially attractive?
From a technical perspective, a push lawn mower doesn’t require nearly as much power as a chainsaw, and can be considerably heavier. So it’s not surprising that electric push mowers are excellent replacements for petrol models, and are with spitting distance on purchase costs. Choice’s reviews generally indicate that customers are extremely happy with their electric push mowers. Like other garden tools, proprietary batteries are a potential problem for commercial users, but overall, small lawn mowers are a solved problem.
But larger ride-ons? Not quite so clear-cut…
While there are literally dozens of mower manufacturers, the American MTD Products is perhaps the largest specialist manufacturer. One of their brands, Cub Cadet, offers an electric lawn tractor built on the same chassis as their petrol models. It can reportedly do an area of 2 acres (roughly one and a half hours of mowing) on a charge, which takes about four hours.
Reviews suggest it works just fine, particularly for domestic use - and, again, the electric versions are infinitely quieter and cleaner. But as of early 2023, the extra costs are not insubstantial.
The most expensive Cub Cadet petrol lawn tractor with a 42-inch (Americans…) cutting deck has has an RRP of $6,999. The equivalent 42-inch electric model costs $3,000 more. $3,000 buys a lot of fuel, even at today’s prices - roughly 1750 litres of fuel. That’s enough to mow over 900 acres (364 ha for the metricated). Put another way, even if your electricity is free, you can mow the largest block the electric mower can do one a single charge 400 times on the fuel you could buy with the cost differential.
Yes, you’re likely to save a little on maintenance, but from personal experience these slightly larger small engines are much more reliable than two-stroke chainsaw or push mower engines. If you change the oil and clean the air filter every so often, they’re likely to run reliably for years. Ironically enough, one of the largest maintenance expenses is replacing the lead-acid batteries used to start the engines.
The technology is mostly there, even for commercial users (we haven’t gone into it here, but some electric models have swappable batteries which solves the endurance problem). But it’s expensive enough that people mostly aren’t going to voluntarily switch just yet. You might take the view that anybody who can afford a place big enough to require a ride-on mower can afford to pay that premium (either directly or indirectly to a lawn mowing firm), and I’d probably agree. But they’re not going to do so right now without some kind of government intervention.
California’s lawns, as much as it still has them after years of drought and water restrictions, will be fine. But the rest of the world’s peri-urban areas will be putting up with the noise of petrol lawn mowers for a while until other governments follow California’s lead.
A quick musical postscript
The world is not exactly overendowed with songs featuring the topic of lawn mowing, but there there is at least one genuine hit recording on the matter. American country artist Buck Owens had a Number One hit on the country charts in 1969 with “Who’s Gonna Mow Your Grass”:
Owens was apparently another strong contender for that hotly contested title “worst scumbag in popular music”, but the song itself has a pretty decent jazz-waltz feel. It’s hard to argue with the description of him “a very bad man who made very good music”.
I mean, sure, there’s footballers and journalists, but surely there’s only one Paul Kelly putting music videos on YouTube, right?
If you’re wondering what the difference between hay and silage, as mentioned in that song, is, wonder no more. Hay is left to dry after cutting, but before baling. Silage skips the drying-out step, and is stored “green” either in pits or, after baling, wrapped in plastic wrap. Just stay out of the way when the wrap is removed, because the stench is like little else.