I recently reviewed the notes I made several years ago, when I had a particularly large garden, on reasonably new ground. To cope with the demand on new ground, I mulched heavily with compost and straw, and found that I had encouraged a large snail population. It is a story I have used many times in teaching, but have not previously written down. There are some useful lessons to be learnt from these observations - we will return to these later. First I have to describe the garden, and the problem.
The garden was made on a low maintenance mulch-garden design. Once made, it survived with the minimum of care. Although the garden covered a quarter of an acre, watering, pruning, tying up and weeding were done hurriedly after the main days work. Some raised beds were made by mulching directly onto the pasture. Other beds were rotary hoed and then mulched. I was overcome with guilt when constructing some of the garden beds. The rotary hoe chopped up a bullfrog - they bury themselves into the soil to hide, emerging on favourable evenings to feed. I will tell more about the bullfrog later.
One serious outbreak of young snails on the bean crop alerted me to the potential problem. I controlled this outbreak with a light spray of copper sulphate - about 40 cents worth of copper from my local pharmacist. I sprayed this out in the early evening, while the young snail were out feeding. Their shells were still thin, and their body weight small. It took very little copper to make them disappear.
This controlled the young snails that lived in or on the crop. The majority of snails lived in the weedy areas surrounding the garden, at the edge of the mulched area. After dark each night, they made their way onto the garden, or the grassed pathways between the mulched vegetable beds, where they fed. Some snails lived under the big leaves of the brassica crops too, but these were easily hunted down and removed. The snails did a lot of damage, and made produce look uninviting. A smaller grey slug was a minor nuisance only, but was also unwanted. The grey slugs mainly fed on the dead brassica leaves, which had fallen off the plant, or lettuce leaves, which were rotting where they were touched the ground.
There were also a good many leopard slugs, and some small brown native snails, which both eat other slugs and snails (the common brown garden snail is an introduced pest). Leopard slugs and native snails can chew plants too, but they generally prefer the high protein diet of other molluscs, and are not a pest while other food choices are around.
I did not observe the resident bullfrogs feeding on snails, but I was reasonably certain they did predate on them and contribute to control. The chickens really appreciated the dead bullfrog (the one I rotary hoed), so it was not wasted.
There were also many blue tongue lizards and some stumpy tail lizards, both readily feed on snails.
So I had four or five known biological controls for snails resident in the garden. I did not want to use chemicals that might harm the predators, and as the snails were maturing, and the shells hardened, the copper was less effective.
The first technique I employed was managing the distribution of snails by controlling the height of the sward on the paths. By setting the blades low, I was removing snail food and shelter. In these areas I could concentrate my hand picking (at night, with a torch). In other areas I let the sward grow. The snails were content to stay there and feed, and did not move so quickly into the garden bed. There had to be a balance between these activities. If I left one area of sward untouched for two or three weeks, another generation of young snails would be on its way.
Each night about half an hour after dark, I wandered out with the torch, and picked all the visible snails off the path. This took half an hour the first night, twenty minutes the second and third nights, and thereafter about ten minutes per night, for three weeks. After that, two or three ten-or-fifteen minute visits per week kept the problem under control.
The snails collected were placed back on the path and crushed. This kept the leopard slugs and native snails off the vegetables.
Watering early in the morning was a useful tactic too. It helped to keep the snails active until the magpies and other birds could get to them.
A pottery snail trapped helped and looked attractive in the garden too. The urn-shaped trap had several entry holes for snails, which could then be conveniently collected during the daytime.
Towards the end of that garden, when I had planted a late crop of lettuce, I became very busy and had to use one application of snail bait. That, and the copper sulphate, were the only pesticides used that year.
If a bait is necessary, there are now iron chelate and copper based pellets available, which should meet certification guidelines.
The following hints may be useful to make hand picking easier and more effective:
- Encourage snails out by watering lightly in the late afternoon or early evening
- Check snails about 45 minutes after dark, they generally follow theit previous silvery trails, emerging from cover such as big leaves, garden edging, under stones, logs or fences
- Provide a home site, such as a board on two bricks, so you have to spend less time searching
- If you step on snails, any eggs about to be laid may still survive (do it in the open, on the path, where the sun will dry them out).
- You can also feed snails to poultry or fish