How to Use Garlic to Eliminate Pests Organically

Aphids, whiteflies, caterpillars – midsummer is definitely peak pest season! But we can fight back with a surprising natural pest solution…garlic!

Why Garlic Foils Pests

The secret lies in the smell of garlic or, more precisely, the chemistry behind it. When you crush or chop garlic, it releases a compound called allicin, a sulphur-containing compound that gives garlic its sharp, pungent aroma. And while we rather like it on our food – I absolutely love the stuff! – most insects hate it.

Allicin confuses insects’ sensory receptors by masking the signals that guide pests to their preferred plants. On top of that, garlic is naturally antifungal and antibacterial, so it does double duty as a defence against things like powdery mildew too. And if pests land on a sprayed plant, the sulphur compounds aren’t just off-putting – on soft-bodied pests they can act as a contact insecticide. This stuff is a remarkably complete package!

Garlic Sprays For Plants

There are two sprays I’m going to make, and I want to share both because they suit slightly different situations.

Simple Garlic Spray

First up is a general spray that’s perfect on any plant, including edible crops, and is also fab spritzed on plants to help repel pests in the first place, before they even become a problem. You’ll need a whole bulb of garlic (around 10 cloves), one litre (four cups) of water, and a teaspoon of ecologically sound, unscented liquid soap such as castile soap.

Start by peeling then blending the garlic cloves with about a cup (0.25 litre) of water in a blender until you’ve got a good, smooth purée. Then add the remaining water and one teaspoon of liquid soap, and blend again to combine. Pour the mixture into a jar and leave it to steep for at least 12 hours. This gives the allicin time to fully infuse into the liquid.

Once infused, strain the mixture through muslin, cheesecloth or a fine sieve into a new, clean jar or jug to remove any remaining chunks of garlic that might potentially block the nozzle of the spray bottle you’ll be using to apply it.

If you’re not going to use your garlic spray straight away, pop it into the fridge, where it will keep for up to a week. After that, the allicin starts to break down and loses its potency, so make fresh batches as you need them.

Garlic spray is particularly effective against soft-bodied pests, which tend to do the most damage in a summer garden. It’s effective against aphids, whiteflies, spider mites, and caterpillars. It’s also good for slugs – or, rather, bad for them! They really don’t care for the garlicky pong, and it’s fab used against carrot flies because the strong scent confuses the flies, making it harder for them to home in on susceptible plants like carrots and parsnips.

Oil-Infused Garlic Spray

My second garlic spray is used as a more targeted pest control, and is especially helpful for reacting to heavy infestations. The oil in this spray helps the allicin stick to leaf surfaces for longer, making it even more effective.

So, for this you’ll need around four to six garlic cloves, some sunflower, vegetable or rapeseed oil, castile soap, and half a litre (about two cups) of water. Start by crushing the garlic, then combine that with two tablespoons of your oil. This can now be left for 24 hours to fully infuse.

The next job is to strain out the garlic – again to prevent clogging up the nozzle of our spray bottle – then add half a teaspoon of liquid soap and half a litre or (two cups) of water. Diluting the garlic-oil concentrate like this is super important. This is a much stronger recipe, and applying it too concentrated could harm your plants, especially in hot, direct sunshine.

Give it all a thorough shake up to mix, and you’re good to go.

How to Use Garlic Spray

Timing really matters when using any garlic spray, as it can potentially affect beneficial bugs as well as the pests we’re looking to target. Always spray in the evening if you can. This is important for two reasons. First, direct sunlight on a wet, oily leaf could cause scorching. But, more importantly, most pollinators are far less active in the evenings. We want to protect plants from the bad guys without bothering the good ones.

Spray both the tops and undersides of leaves, where pests like to hide and lay their eggs. Hold the bottle 6-12 inches (15-30cm) from the plant and aim for a fine, even coverage, not a drenching. If you’re tackling an active infestation, use the oil spray every two to three days, as well as after any rain, which will wash it off. For the preventative spray, once a week is plenty.

One more tip, before you start, is to test-spray first. Spray a single leaf, wait 24 hours, then check there’s no adverse reaction. The strength of homemade sprays can vary depending on the variety of garlic you’ve used to make it, so it can be worth a quick check, especially on seedlings or tender young plants.

Garlic as a Companion Plant

Garlic doesn’t just work in liquid form though. Simply growing garlic near vulnerable crops offers a surprisingly effective means of passive defence, because those sulphur compounds are released into the soil and air while the plants are actively growing.

Roses and garlic are a classic pairing. Garlic planted nearby can help protect against aphids and even reduce black spot. Tomatoes benefit too, as garlic helps deter spider mites and aphids, and it may even enhance the final flavour of the tasty toms you pick.

Brassicas – that’s cabbages, kale, broccoli, cauliflower and other related crops – are another great match. Garlic confuses and repels the moths and butterflies that love to lay eggs on brassica leaves. Garlic also gets along with strawberries, carrots, peppers, and many more plants, For a full list, check out our Garden Planner. Select the garlic on your plan then click the Companion Planting button to see the really rather long list of plants that garlic actively helps. Just remarkable!

Of course, garlic won’t replace every pest control option in your toolkit, but as a safe, cheap and effective line of defence, it’s hard to beat. And so, for that matter, is the Garden Planner. The Companion Planting feature is just one of many powerful features it offers, including crop rotation and personalised sowing, planting and harvesting schedules. Give it a go – it’s free to try for 7 days, and you won’t have to input any details either.

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