How to Make All-Natural Pest Repellent Using Marigolds

If you’re tired of pests playing havoc with your garden, there’s an all-natural spray you can make from a flower you may already be growing: French marigolds (Tagetes patula). In fact, there are many ways marigolds can protect your garden, so I’m going to show you what these are and the most effective ways to use them.

Make a Natural Marigold Pest Repellent

There’s a lot of often contradictory advice surrounding marigolds. In their natural state they’re in fact susceptible to a fair range of pests, just like any other plant. And in fact, many gardeners use that to their advantage, planting marigolds as a trap crop or sacrificial crop near vegetables so the marigolds intercept the likes of aphids and get struck first. Then once infested, they can simply be dug up and removed along with those pesky pests, sparing your crop plants.

Marigolds are often touted as a go-to pest-repelling flower, but not all the claims made for it are true: they won’t deter deer, slugs or snails, all of which are in fact rather partial to marigolds, and they won’t repel bugs like spider mites and aphids – or at least, the unprocessed plant won’t. But marigolds contain certain compounds which, once extracted, can be used to massively reduce the risk of pest attacks. We can unleash the pest repelling properties contained within the plant, giving us a truly versatile spray.

Start with two packed cupfuls of leaves, stems and flowers. Crush them up using a pestle and mortar, or even just tear up the plants with your hands, place them in a bowl, and bash them up with a rolling pin as a cheap and cheerful alternative. Alternatively, pulse it all up in a blender.

Add four cups (about 1 litre) of water, then rest it in a cool, dark place for about five days to allow time for the compounds in the marigolds to seep out into the water.

Then strain the liquid off through cheesecloth or muslin. Give it a good squeeze to get every last precious drop. If you don’t have this sort of cloth then a dish towel or even a pair of old tights should do the trick I reckon.

To use the marigold concentrate simply dilute it with equal parts water. You can also add a few drops of castile soap, which is a natural, plant-safe soap that will help the spray stick to the foliage rather than rolling straight off. Give it a good mix and pop it into a spray bottle.

Marigold spray is a preventative, applied to plants as the risk of pests increases but, ideally, before they’ve actually arrived. Just spray it onto plants about once a week – more often if it’s rainy – to help protect plants such as cabbage family vegetables that are particularly susceptible to an aphid or caterpillar attack.

The Ultimate Companion Plant

Another way to prevent pests is to grow marigolds alongside at-risk plants, because there are a few select pests that it will repel as it grows. Research from Iowa State University found that interplanting courgettes with marigolds improved their resistance to squash bugs and cucumber beetles, so for North American gardeners this could be something worth replicating in your own garden as a strategy to outwit those particularly bothersome bugs.

But perhaps the most common marigold pairing is the tomato, where it’s said to deter whitefly – a claim backed up by generations of gardeners. But a recent study by Newcastle University suggests there’s some legs to this, though perhaps ‘confusion’ is a better word to describe its conclusions.

Using large-scale glasshouse trials, the study found that planting marigolds alongside tomatoes really did slow the growth of whitefly populations. That’s because marigolds produce limonene, an aromatic compound also found in citrus. They release it as they grow then, as it becomes airborne and spreads, it helps mask the tomato’s own aroma, making the tomato less obvious to whitefly, which rely on odours to detect host plants. It’s as if the tomato has pulled on an invisibility cloak!

To max out this effect you’ll need to plant your marigolds at same time as your tomatoes so they’re protected from the start. Or if you’re in a warmer climate, plant a month or even two months ahead of your tomatoes to give the marigolds extra time to bulk out and release even more limonene right from day one of your tomatoes.

I aim for at least one marigold to every two tomato plants in my garden. They’re most effective in enclosed environments like a greenhouse or tunnel where the limonene won’t get carried off by the wind, but I include them with my outdoor toms too, as they’ll still have some impact and will attract a legion of beneficial bugs too.

Control Nematodes With Marigolds

If you’ve ever suffered from root-knot nematodes, you’ll know how difficult they can be to get rid of. Adult females lay their eggs into little galls they create on the roots. The hatched young then feast on the roots, weakening plants and making them less productive and, in many cases, even killing them.

Well, would you believe it, marigolds can help control root-nematodes too! This time the impact is coming from the roots, which exude alpha-terthienyl, a chemical that’s toxic to the nematodes. It kills them on direct contact, and inhibits egg hatching.

But note the word ‘direct’ there. Growing marigolds next to at-risk plants won’t have much of an impact because the alpha-terthienyl won’t penetrate into the soil that far. To get the best effect we need to spread it about throughout the soil, and the simplest way to do that is grow them until they’re about foot tall before cutting them down and digging the whole lot in. Do this and you’ll enjoy a double whammy of compounds found in both the foliage and roots, making the soil a pretty hostile place for chancing nematodes.

Grow marigolds densely as a cover crop or green manure in the same area you’ll grow your vegetables. And just like any other cover crop, those dug-in marigolds will add extra organic matter to the soil, contributing to its overall fertility and structure.

In time, root-knot nematode populations will recover, so if they’ve caused you headaches in the past consider including marigolds as part of your crop rotation plan to naturally cleanse the soil ahead of susceptible crops. Or for those in cooler climates or with a shorter growing season, try mustard as a fast-growing alternative. It can be sown towards the end of summer once most vegetables are done.

Attract Beneficial Bugs

Perhaps the biggest selling point for including marigolds in your garden is the long list of beneficial bugs they attract. Bees and butterflies, of course, but also ruthless predators that devour pests like ladybirds, lacewings, parasitic wasps and hoverflies (syrphid flies). Bugs like these create a thriving, balanced garden ecosystem where pests rarely spiral to problem levels.

For this reason alone, I reckon it’s worth dotting marigolds here and there throughout the vegetable garden, where they’ll also add little pops of colour to cheer up even the weariest gardener.

Marigold is one of many fantastic companion plants you’ll find in our Garden Planner. Add marigolds to your plan, select them to highlight them, then click the Show Companions button to see some of the crops it has been proven to benefit – very handy!

Even More Reasons To Grow Marigolds

I love marigolds because they grow in most soils, even fairly poor ones, and they can tolerate both heat and spells of drought. It’s easy to start them from seed – sow them direct in warmer climates or into pots or trays in cooler climates to get them underway before your last frost date. After sowing them I just secure some clear plastic over the top of the pot to keep them moist and cosy, bring them indoors into the warm to germinate then once the seedlings are up, transfer them into their own pots or plugs to grow on til frosts have safely passed and I can plant.

Pinch off old flowers to encourage new ones that will keep the show going for longer. Then at the end of the season leave a few flowers to produce seeds to collect and sow next spring – it’s super-easy to do, and home-saved seeds provide fantastic results. In fact, even after a frosty winter I’ve had marigolds pop up where I grew them the previous year, giving me fantastic little plants to relocate elsewhere in the garden.

Remember you can eat marigold flowers too, which have a slightly citrusy tang – thanks to all the limonene no doubt. Try adding petals to salads for a touch of colour or pop them into drinks for a punch of pizzazz. Plucked petals will also give a yellow tinge to the likes of rice and puddings, earning marigolds their reputation as ‘poor man’s saffron’.

As I said earlier, you’ll find marigolds among our copious selection of flowers (and vegetables, fruits, herbs and shrubs) in the Garden Planner. Be sure to put it through its paces for free with a seven-day trial.

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