A simple homemade spray using a 50p garlic bulb can banish pests from gardens, according to horticultural expert Benedict Vanheems. He advises making your own insect repellent instead of relying on harsh chemicals.
Garlic releases allicin when cut or minced, a sulphur-containing compound that gives it a pungent aroma. Benedict explains that allicin confuses insects' sensory receptors, masking the signals that guide pests to their target plants. It also acts as a natural anti-fungal and anti-bacterial agent, helping against powdery mildew.
How to make the spray
To make the spray, use a whole head of garlic (around 10 cloves), a litre of water, and an ecological soap such as Castile soap or Ecover's multi-purpose cleaning liquid. Peel the garlic, blend it with about a cup of water into a slurry, then add a teaspoon of soap and more water. Mix well and leave overnight to infuse.
The next morning, strain the liquid through a fine sieve or muslin cloth to remove particles that could block a spray nozzle. Use it immediately in a spray bottle, or store it in a jar in the fridge for up to a week. After that, the allicin breaks down and becomes less effective.
Effectiveness and application
The garlic spray is particularly effective against soft-bodied pests like aphids, and slugs cannot stand it. It also works against carrot flies, confusing them and making it hard for them to target crops like parsnips and carrots.
For more acute infestations, Benedict recommends adding two tablespoons of sunflower, canola, or vegetable oil to the mixture and leaving it for at least 24 hours. Then dilute with at least half a litre of water, as the concentrated spray can harm plants if not diluted enough. Always do a patch test on sensitive plants first.
Spray in the evenings to avoid scorching leaves in direct sunlight and to protect pollinators, which are less active then. Apply two to three times a week during an infestation, or once a week as a preventative measure, with a supplementary spray after heavy rain.
