Five home remedies traditionally used by gardeners to deter slugs and snails have proved ineffective in the first study of its kind by the RHS.
Copper tape, horticultural grit, pine bark mulch, wool pellets and egg shells proved to make no difference when applied to lettuce. Gastropods inflicted the same damage to those treated with the remedies as without. However, lettuces that benefitted from a layer of wool pellets or pine bark yielded a 50% bigger crop as the treatments acted as a fertiliser and mulch.
The RHS recommends that gardeners encourage garden predators, employ other cultural controls such as physical removal or traps. Failing that, if damage is intolerable, turn to scientific deterrents such as nematodes and slug pellets. The latter used strictly according to the manufacturer’s instructions to minimise risk.
108 lettuces were sown in a series of pots and raised beds at the charity’s John MacLeod Field Research Facility in Wisley. These were treated with alternate control methods, including no control at all. The lettuces were grown for six weeks before harvest and the leaves of each lettuce examined using a leaf area meter that calculated the proportional damage. The lettuces were then dried and weighed to establish yield.
Lettuces planted in the ground were more susceptible to slugs, with 5.7% of each eaten on average. This compares to 0.2% of those in pots, which, despite this advantage, still yielded less crop. The ready availability of lettuces at ground level is thought to help minimise damage to pots.
The RHS Lindley Library found that gardeners have turned to home remedies since the 1600s to counter slugs and snails. Those tested in the experiment were thought not to work. This is because, the thick mucus of slugs and snails acts as a protective shield, enabling them to glide over the barriers.
The two main gastropod culprits in the experiment were the grey field slug and common garden snail. Gardeners are being reminded of the benefits of some varieties to gardens. These include the green cellar slug which feeds on mould and algae and the leopard slug that prefers fungi and rotting material.
Dr Hayley Jones, Entomologist at the RHS and lead researcher said:
“Our study reveals that many gardeners could be wasting time and money by turning to home remedies in a bid to protect their prized plants. With the likes of egg shells, barks and mulch so far proving no discernable deterrent to slugs and snails we would recommend using proven formulas like nematode biological control if the damage is too much to bear.”
The RHS will continue to test slug and snail home remedies, investigating other factors. These factors include whether environmental conditions and local slug populations make a difference. The RHS also plans to test alternative control methods such as beer traps and is currently working to investigate ways to combine scientifically proven control methods into pest management strategies.
For more information about garden slugs and snails as well as other pests and diseases please visit www.rhs.org.uk