I found myself asking this question this morning when sitting outside with my son waiting for the car to take him to daycare. I was staring at the sky, he was staring at my peas, and we saw this:
I’ve always known “what snails eat”, like any gardener – it’s whatever you’ve just planted. Right? Which is partly true. They also eat cardboard and limestone, but that’s another story. But they do have preferences, those plants which no matter how often you plant them the snails just seem to take out. My red-and-green kangaroo paw (Anigozanthos manglesii) is ground zero in my native garden, and the species has a reputation for it. I planted several young plants earlier this year before the weather became damp enough for the snails to wake up. I was hoping they’d get enough of a foothold to resist the inevitable advances, like my peas here which are still flowering, fruiting and growing madly despite the damage. But this morning after a damp and drizzly night I checked, and sure enough my plants had been eaten. Not the outer leaves, either, but just the growing centre without which there will be no flowers and no more leaves. Unless they’ve stored enough energy in their roots by now to generate new clumps (it’s a clumping plant but the timing is dubious), those plants are now toast – even though they still have 90% of their green matter left. I have several other species/varieties of kangaroo paws in the garden, including a second type interplanted with the manglesii. They are still largely untouched. Occasionally I’ve found snails living in them, sometimes in huge numbers, but they don’t harm the plant. The manglesii? It’s like the snails have a genocide mission. They’ve made their way past all the other plants – including fresh young grass seedlings with soft green leaves – and wiped the manglesii out.
Snails do have a preference for anything soft and green. The common garden snail doesn’t seem to really like grasses of any kind much, except as a place to sleep. It also leaves most of my hard-leaved drought-tolerant natives well alone. We have native species of snail that go for those, but our feral snails don’t like them. Seedlings are very popular, I’ve lost a lot of my seedlings to snails while waiting for them to get one more leaf so that I can transplant them. I even began growing the seedlings in boxes of water so that I could have a water barrier between them and the snails. Tip: this works, as long as you remove the bean seedlings before they get tall enough for the snails to use as a ladder. Seedlings are young, fresh, full of whatever it is that snails love to eat. Which I haven’t identified yet but basically it’s whatever it is that we humans like in vegies too. Which is probably a complete lack of anything resembling vitamins or flavour, if the popularity of iceberg lettuce is anything to go by. I think of it sometimes as “life force”, because they seem to zero in on plants, and the parts of plants, that are growing quickly and vigorously. Those pea tendrils above? They’re at the top of the plant. The snails climbed two metres of swaying string and vine to get to them, and ignored most of the other leaves on the way.
Snail-proofing a garden is tricky. I’ve been working on it for a while. You can’t just remove snails and throw them over the fence – snails have memory and a really good sense of direction and they will, however slowly, come right back to where they remember finding that really tasty meal. Using certain plants as snail bait is one thing I’m looking at. The pea screen is actually my key example here – the pea vine that got well established before the snails woke up is in fact doing fine regardless of the damage. The pea vines that didn’t quite make it to two tendrils by S-Day were eaten off at the base of the stem. Healthy well-established plants resist snails. So if you have good plants of a type that snails will travel for, you can direct them where you want them. However, that assumes you don’t actually mind low productivity on those plants. For instance, I’d *really* like to have my red-and-green kangaroo paws make it to flowering. And they don’t.
Most non-poison-using gardeners end up opting for physical barriers. As I did with the water around the seedlings. Crushed eggshells (didn’t work on my bean screen last year), crushed limestone (wait, don’t they like eating that to strengthen their shells?), a sheet of copper flashing (expensive but reliable if your target plants are grouped). Coffee grounds are my favourite, and what I will try next time if I plant any more kangaroo paws. Interestingly, it’s not the texture of the coffee grounds that puts them off, as I had assumed, it’s the caffeine. Snails don’t like eating caffeine – and maybe the question to ask when snailproofing is what they don’t like to eat, as well as what they do. You can in fact make an anti-snail soil treatment using coffee. Real coffee, the good and strong stuff, espresso rather than instant. Dilute it 1:10 with water and spray it on the soil around the plants you need to protect. I may try that with my summer seedlings when I plant them out. It’s only a temporary solution, it washes out of the soil so you need to reapply it after rain, but it’ll be worth trying with the seedlings I plant in September and October (August has a lot of continuous rain). Which (tell the truth) aren’t usually too badly hit by snails anyhow as the snails are going to sleep by then, so I don’t know if I’ll get a proper test of the concept. But we’ll see. Many years ago I tried a similar soil spray using a commercial copper-based preparation and wasn’t convinced, for much the same reasons. But it does mean no physical substance that can be played with, dug up or eaten by children and pets.