Managing garden pests as an organic gardener
Updated: May 11
Organic gardening is about building the soil and creating a healthy ecosystem, as opposed to conventional farming, that only tends to take away from the soil. As an organic gardener, you aim is to create an ecosystem that helps you manage your pests, not to eradicate all pests. Indeed, you might hate aphids on your beans, but ladybirds and lacewings eat them. It’s all part of a big web of life, and as an organic gardener, your job is to support that web.
So, how do you do it? Well, the first general three rules to keep a healthy garden and manage your pests are:
Grow healthy plants
Know your common pests life cycle
Use a mix of techniques to keep pests at bay
Growing healthy plants seems obvious, but hear me out. Plants have been on earth for much longer than us, and contrary to most animals, plants can’t run away from threats whether it’s a sheep about to munch them, or a sudden onslaught of aphids. And so, they have developed ways to defend themselves without running away. From spikes to chemicals, healthy plants have an entire array of defence mechanisms that are very efficient: the earth is pretty much covered in plants. So by growing strong healthy plants, you make sure their natural defences are there and ready to be used. It’s not always enough, but it helps.
Growing strong plants means using good soil and ensuring the soil stays healthy by using compost tea and worm cast. It also means transplanting seedlings in their final space a little later, once they are strong enough, even if it means transplanting them in a bigger pots and keeping them under cover/ in a greenhouse a little longer.
Know your common pests live cycle is crucial.
Get to know what’s hanging out in your garden, because it’s fascinating, and it may really help understanding when you can act to stop something munching on your prizes vegetables. It’s much easier to stop a white cabbage butterfly laying eggs on your brassicas, than it is to manually pick the caterpillar once they are on a feeding frenzy. And knowing what ladybird larvae look like (see picture), will ensure you don’t get rid of them: aphids are their favourite foods.
And finally, you need to use a mix of techniques to keep pests at bay. I have classified them in 5 different category (all detailed in the text below):
Physically protect your crops by ensuring pests can’t access them
Deter pests or manually remove pests
Take away pests habitat/ check pests habitats
Attract pests predators using the right habitat, food and companion plants
Use biological control
Physically protecting your crops by ensuring pests can’t access them is the easiest and most straightforward way of managing pests: if they can’t get to your crops, they can’t eat them! This includes:
Netting all your vegetables again the cabbage butterflies (small net is needed)
Netting your prizes veg and fruits against pigeons - see photo
Use rings on individual vegetables against slugs and snails (hand made ridged water bottle rings work well, make sure you haven’t trapped a slug IN the ring) while copper tape and Slug Gone (compressed wool pellets) also make it more difficult for slimy garden pests to reach your plants
Deter pests or manually remove pests means using ways to make pests go away, or picking them up as and when you see them. For example:
Pick up any cabbage butterfly caterpillar you see (you can generally spot their miniature round poo before you see the culprit)
Use garlic spray to deter slug, snails and actually kill aphids (1 crushed head of garlic with its skin, in 1 litre of boiling water, let it cool down, strain it through a cloth in a spray bottle, use liberally)
Take away and/ or check pests habitat
It stops pests from using your garden as a bed and breakfast. For example you should check regularly under all your pots for hiding snails and slugs (and their eggs - see photo of the garden slug and eggs I found under one of our pot). Any drain, in between the lining of the planter and the planter itself are also ‘hot spots’ for slugs. Remove them manually, and dispose of them- I used to put my slug harvest in a small bucket, and drop them off in a park's hedge where they could do no damage.
Attracting pests predators using the right habitat, food and companion plants is at the core of creating a balanced ecosystem. To so this, you can do some (or all ) of the following:
Use companion plants like pot marigold (calendula) to attract lacewings whose larvae will feast on aphids.
Keep some wild areas in your garden, as they will promote the creation of a balanced ecosystem and encourage hedgehogs, birds and insects that will eat your pests
Attract birds and beneficial insects by providing bees drinking stations, insects houses and bird houses (make sure your birds houses face north)
Finally, the holy grail of wildlife habitat is of course water: build a pond (it doesn’t have to be big to attract wildlife- see the RSPB advice on building ponds) and watch as frogs, damselfly and other insects start showing up in your garden.
Biological control is quite a strong approach to controlling pests, but if you have a big garden or an infestation, it might be the most effective thing to do. Biological control means using a natural predator or parasite of the pest you are fighting against. In safe biological control, you use a predator/ parasite that already exists naturally in the environment and you simply add more so it can deal with your infestation. Once the pests have all been infected, the predator / parasite will simply die off as it has no more prey/ hosts to consume/ infect. It is safe to all other animals, as well as humans.
Unfortunately, there have been plenty of times when humans used biological control inappropriately and ecological disasters ensued like the cane toad in Australia and the Harlequin ladybird in Europe, but here I am talking about the non invasive biological control that is safe to use in European gardens. More specifically, I want to talk about nematodes: nematodes are tiny roundworms invisible to the human eye, and they naturally live in the soil. There are around 15 000 species of nematodes, and you can find up to a few hundreds of nematodes per teaspoon of healthy soil.
Nematodes for slug control: Phasmarhabditis hermaphrodita is a natural parasite of slugs. As a result of the infection, slugs will stop eating after 3 days, and die within 10 days. Slug nematodes are ineffective against snails, and not all the species of slugs will be affected- the Spanish slug is immune for example.
Nematodes for Vine Weevils. Vine weevils grubs will consume plant roots and are difficult to spot until your plants start dying and it’s too late to act. Steinernema Kraussei nematodes will infect vine weevil larvae and kill them quickly.
When receiving nematodes, you need to strictly follow the procedure to spread them or they won’t work. Nematodes need to be used quickly and kept in the fridge in the meantime so make sure your nematode package is delivered where you can pop it in a fridge immediately.
It is obviously heartbreaking when your prized vegetables get munched, but I like to remember that most ‘pests’ were here before humans, and they are just trying to get food too- it just happens that we grow great food for humans and non humans. So I am going for the 80-20 rule: I am aiming to get 80% of my crops, and 20% of my crops are shared with the rest of my garden’s inhabitants (meaning, I don’t get to eat 20% of my crops). It's a good compromise for my small garden!