If I had a pound for each time I heard somebody recommend crushed egg shells as a slug and snail barrier I’d be rich. The problem is, it’s mostly a load of old cobblers which never ever gave my plants any kind of protection whatsoever. In frustration lots of gardeners resort to using old fashioned Metaldehyde slug pellets which then kill birds and hedgehogs higher up the food chain (making your gastropod problem even bigger). But what are we growers meant to do in the face of the slippery slimy munching onslaught destroying our Dahlias and Cucumbers? Well, I’ve done some tests, filmed them (because words are cheap…) and I have some natural alternatives.
Firstly here’s the evidence on egg shell failure, this is the fifth time I tested them, with three separate snails and two slugs, each time they’re away in under 90 seconds. In response from the ‘egg shell deniers’ I’ve had “Your egg shells are too small”, “Your egg shells are too big”, Your egg shells are too wet” etc. They were all baked and crushed and no matter how many I put down they are no barrier at all. Slugs however do like to eat them – so there is a slight chance that slugs will be dissuaded from eating your plants when presented with a meal of egg shells as an alternative. The next night they’ll be back fatter and hungrier to eat your plants:
Oh and salted Pistachio nuts don’t work either, here I held them in place with egg shells to stop the snail pushing the Pistachio shells out of the way, it looked good at first but with a run up he was away!:
Dry fine powdery ‘stuff’ works
In my tests snails will not cross a barrier of dry fine powdery ‘stuff’ – it’s pretty obvious that it sticks to them, they can’t get any traction to climb over it but the granules must be small. A half cm tall and 2cm wide barrier of Gypsum, Talcum Powder, Soot, Wood Ash, Readybrek, Chilli Powder, Coffee Grounds or Flour is a possible option if:
a) It doesn’t rain
b) It’s not windy
However… given that we reside in a wet and windy country and that’s when slugs and snails emerge, it makes any dry powdery solution quite unreliable unless adequately covered (possibly fine in a greenhouse). It’s also important to be careful what you’re putting on your soil, for the most part wood ash and gypsum are not too bad but long term use of wood ash could alter your soil’s ph (gypsum has a neutral ph). Where rats or mice are an additional problem, readybrek or flour might encourage them into your garden or allotment and give you a whole different problem.
Sharp stuff with tiny compacted thorns works
It turns out that a wall of horizontal short thorns is neither edible or crossable (trust me I watched the snails with their tiny little mouths trying to demolish thorns and failing). In my video below I tested brambles, others have mentioned roses to me (varieties with high thorn density, not those with finger wide stem gaps). I think either would do nicely; wearing thick gloves cut them into short straight, leafless stems and build complete barriers around the base of your plants, snails can’t cross them. Slugs have the advantage of being shell-less and slightly more flexible in that regard, they could burrow beneath the spikes, but I’m not sure they would really bother.
The best solution? A combined approach for all weathers
I favour a dual approach to plant protection using both a powdery substance AND bramble stems. The powdery substance is gypsum which in tests was by far the best repellent to snails and inedible. Gypsum contains calcium and sulphur which is also good for your plants, it helps to condition soil and therefore has an added fertiliser benefit for use as a snail barrier. A low flat DRY layer of gypsum, 2cms wide with a bramble barrier on top of it is the perfect gastropod plant protector. As the wind and rain washes the gypsum into the soil the thorny stems will remain until you have time to reapply the gypsum. If you’re worried about long term gypsum use then consider rotating it with epsom salts which will add magnesium to your soil – critical for plant growth.
Summary of Snail Barrier Performance:
|Material Tested||Works Dry?||Works Wet?||Notes|
|Egg Shells||NO||NO||Slugs do eat them (so might mice & rats)|
|Pistachio Nut Shells||NO||NO||Might attract mice & rats)|
|Readybrek/Oats||YES||NO||Snails and slugs eat them (so might mice & rats)|
|Flour||YES||NO||Snails and slugs eat it (so might mice & rats)|
|Talcum powder||YES||NO||Not good for the soil|
|Chilli powder||YES||NO||Doesn’t burn gastropods but would mice and rats so better than Readybrek/Oats or Flour|
|Gypsum Powder||YES||NO||Fertiliser benefits (calcium and sulphur).|
|Soot or Wood Ash||YES||NO||Possible soil ph implications for long term use.|
|Brambles or roses||YES||YES||Dry brambles first, take care when cutting!|
Organic Slug Pellets
I have had some success with iron based slug pellets, they don’t have an immediate impact and do seem to take some days to take effect but I think it might be worth adding a sprinkle of these organic pellets in addition to the ‘combined approach’ in a very bad year. Organic pellets aren’t cheap though and one tub can just about cover my allotment beds twice. I’ve also got toads, I worry about them even with organic pellets – all that iron might make them constipated.
Slugs do so enjoy eating the bodies of their former comrades, and I have been known to use this to my advantage. On an after dark visit to the allotment, armed with a torch, I gather up slugs and snails by hand from plants and place them together on a plank of wood. This is my ‘stamping wood’ and it does what it says on the tin, I line them up and give them a quick death by boot. By leaving the entrails you’ll find the next night there are more slugs feeding on the dead bodies. Once found, stamp on them too, and so it goes on. I can kill 250 a week using this labour intensive technique.
Finally there is another great article summarising tests conducted by Pumpkin Beth ‘Protecting your Plants from Slugs and Snails‘ – well worth a read, where Beth has conducted actual controlled tests around plants I have relied on my kitchen experiments to back up my thinking. Between the two methods there would seem to be some synergy.