There is no pest I hate more than the dreaded aphid. Greenfly or blackfly, this sap-sucking insect isn’t welcome in any garden, but every single year it never spares mine. So I learned to just accept it and prepare my arsenal of weapons for when it’s time to fight it.
The internet is filled with advice on how to fight aphids. Since I’m plagued with both greenfly and blackfly in my organic garden, I’ve tested my fair share of methods, from classic insecticidal soaps to essential oils and pretty sacrificial flowers.
In this article, I’ll show you exactly what worked for me and, hopefully, what will work for you too.
When do aphids attack and which plants do they prefer?
You can’t be prepared for a fight with the dreaded aphids unless you know when aphid season begins. For most temperate, Northern-hemisphere climates, aphid invasion starts in May.
During the month of May, aphids will multiply like crazy, only to go down in numbers by mid-June. But if you don’t intervene, they won’t disappear completely, and can even last until temperatures start to drop again.
There are many perennials and annuals that fall prey to aphids, and I won’t pretend to know them all. Fruit trees in particular can get affected by greenfly in late spring, leaving annoying residue everywhere, but I won’t cover that here, I’ll just focus on what’s inside my tiny garden.
So here’s a list of shrubs and vegetables that get infested by aphids every year, without fail:
Greenfly:
- Red currant
- Black currant
- Dill
Blackfly:
- Broad beans
- Runner Beans
- Beets
- Celeriac and celery
- Carrots
- Peppers
- Certain flowers (zinnias, cosmos, nasturtiums)
There are plenty of crops that don’t seem to be bothered by aphids – like plants from the cabbage family (but they have their own problems), lettuce, onions and garlic, tomato seedlings, and more. If they’re among your favorites, rest assured they’ll be fine.
But if you’re worried about the crops mentioned above, here’s what to watch for at the beginning of the season:
Symptoms of an aphid attack
1. Increased ant activity
The relationship between aphids and ants has been well-documented. Basically, ants like to “farm” aphids by giving them a ride at the top of the plant. Once settled there, aphids multiply, feast on the plant’s sap, and secrete (ehhmm…poop) a sugary substance called honeydew.
Ants feed on this honeydew, and even “milk” the aphids by stroking their abdomen (weird, I know). Now, there’s no need to go full-on National Geographic here, all you need to remember is this:
If you see ants busily going up and down a plant, you’d better take a closer look at what’s going on with that plant.
Even better, when weeding and tending to your seedlings, take inventory of all the anthills you find. You’ll find out why later in this article. In the meantime, if you want to learn more about ants, check this article.
2. Shriveled-up leaves
While some aphid attacks are obvious (you can clearly see aphid colonies on the stems of plants like black beans or flowers), other crops are more discreet when suffering from aphid invasions, but the consequences are just as negative.
Leaves that shrivel up and change color to a reddish tint are often a sign of aphids, green or black, especially in annuals like beets or perennials like black or red currant. Here’s an example of the damage:
So check underneath any leaves that look suspicious for signs of these small and sneaky pests.
3. Stunted growth
May is still early in the season for many crops, and aphids will strike when plants are just out of the seedling stage. Since they’ll be sucking precious nutrients out of the plants, they won’t develop at the same rate as unaffected plants.
4. Poor harvest
At harvest stage, it’s too late. You probably noticed the aphids multiplying but failed to control them and save your plants. Perennials are usually safe from extensive damage and they’ll recover, but many annuals won’t do so well.
Aphids not only feed on stems and leaves, but they attack flowers as well, especially on beans and broad beans. No pollinated flowers equal no harvest in their case, and stressed beets, carrots, and other root vegetables will develop poorly.
In the case of broad beans, you can pinch the top once the plant matures to prevent aphid infestation – and this article goes more into depth.
3 natural methods guaranteed to kill aphids (if used together)
If you’re reading this blog, you’re probably a fan of organic gardening and want to keep your pest control methods as natural as possible. So let’s explore some non-toxic options to help you get rid of aphids:
1. Spray aphids with Neem Oil
You might already be familiar with neem oil, but if this pesticide is new to you, know that it’s natural and safe, in moderation. Neem is a naturally occurring pesticide extracted from the fruits and seeds of neem, a tree in the mahogany family.
Neem has many uses in the garden. It kills soft-bodied insects on contact as well as renders the plant unattractive to other pests. Aside from successfully killing aphids with it, I use neem oil regularly to prevent early blight or powdery mildew.
- What you’ll need:
Neem Oil – make sure to get more than enough, you’ll need repeated applications;
Backpack or handheld pump sprayer – depending on the size of your garden;
Castille soap – or dish soap, to help mix the neem oil and help kill aphids. - Neem oil 2% spray recipe:
To every gallon of WARM water, add 4 tablespoons of neem oil and 2 tablespoons of liquid soap. Add the soap to the water first and shake well to mix. Next, add the neem oil and give it a good shake.
Beware, this mixture is more concentrated than the regular use of neem oil. It will STINK, so don’t wear your favorite clothes and don’t let it get in your eyes.
Try to choose a sunny day when spraying with neem, ideally a forecast of several sunny days. The neem & soap combination will quickly dry out the aphid’s delicate bodies. If it rains the next day, spray again. Spray once a week for 2-3 weeks and you should see immediate results.
The second day after spraying the aphids should be dead and dried up, much like in this picture:
- Caution: As you spray your garden with this mixture, neem oil may land on your favorite fruits and salad greens. Make sure to wash them well before consuming them.
2. Pressure spray the aphids off the leaves
Who would’ve thought that something as simple as water could get rid of aphids? I discovered this after a severe aphid infestation on my beets. I wasn’t familiar with neem oil at the time, so I pressure washed the beet leaves one by one, for several days, until the aphids were completely gone.
While this is not a permanent solution – since ants can bring aphids back – it’s a great way to hold them off for a while, or as a second measure if you missed any spots while spraying with neem.
- What you’ll need:
A garden hose and hose nozzle with the flat setting. - How to use:
Hold each leaf individually in the palm of your hand, inspect it for aphids, and spray the back of the leaf with a blade of water until all aphids are gone.
Adjust your hose nozzle to the lowest possible pressure to avoid hurting the plants. The leaves will look a little droopy and sad for a day or two, but they’ll quickly bounce back. Check the leaves again after a couple of days – you’ll be amazed at how quickly aphids can multiply. Repeat the procedure if necessary.
3. Kill ant colonies with borax
Since ants and aphids have a symbiotic relationship, killing ants will not only solve your aphid problem faster but will also prevent further infestations in future years. The most non-invasive natural solution I found is borax.
Borax is a naturally-occurring mineral. In small quantities, it’s safe for plants, animals, and humans, but if ingested by ants, it interferes with their digestive system and kills them.
Borax doesn’t work instantly, but we don’t want it to. Ants die within 24-48 hours, after sharing their food with the rest of the colony.
- What you’ll need:
Borax, powdered sugar, and water. - How to use:
Mix powdered sugar and borax in a ratio of 3 to 1. Add water just enough to turn it into a thick paste. Place spoonfuls of this mixture close to (but not directly on) any anthills you might notice in the garden. Avoid placing it too close to your vegetables.
Hopefully, the ants will take the lethal borax straight to their queen, but if you still notice intense ant activity you can repeat the applications. Left unchecked, ants will multiply in the garden over the years, killing seedlings in the nest’s vicinity and farming aphids in early summer.
Aphid control methods that don’t work
There are certainly more things you could do to get rid of aphids, and I haven’t tested them all. Here’s what I tested, though, and haven’t found very helpful:
1. Marigolds
I’m a passionate gardener, so marigolds have a very special place in my garden. They rarely get attacked by anything and keep all kinds of pests at bay. I plant them in between rows of cabbages, and tomatoes benefit from them as well.
We’ve written extensively about which type of marigold to plant, as well as where to place them in the garden.
In the case of aphids, however, marigolds don’t do much. I’m not swearing them off completely, it’s just that in my climate, in late May and early June, marigolds are too small and immature to do anything. But you can certainly give them a try, if anything, they’re pretty and help with pollination.
2. Trap crops
Some gardeners suggest planting nasturtiums next to susceptible crops like beans, so that nasturtiums get hit instead of your precious vegetables. I hoped this might work, but my beans were infested regardless of the amount of nasturtiums around them.
Zinnias and cosmos are among the aphids’ favorites too, and while I don’t plant these flowers as a trap crop, they always get attacked by aphids. Unfortunately, the vegetables in their vicinity don’t get spared either, so I guess it’s just more food for aphids.
3. Ladybugs
I love ladybugs. In fact, I love them so much that during a ladybug freak infestation at the beach I collected as many as I could in a jar to release them in my garden, hundreds of miles away.
Some gardeners even order ladybugs online and that’s wonderful, it does help the garden to some degree.
In my experience, even though I’ve seen ladybugs feed on aphids in my garden, it just wasn’t enough to keep aphid population under control.
Encourage ladybugs to stay in your garden, but when it comes to aphids, don’t get your hopes up.
Conclusion
Organic pest-deterring options may seem overwhelming to a new gardener, but don’t let too many choices put you off. In your fight with aphids, do these 3 things and I guarantee you’ll be successful:
- Spray them with neem oil on a sunny day and repeat applications 2-3 times;
- Pressure-wash the aphids off leaves;
- Kill the farming ants with a sugar and borax mixture.
And that’s it. It takes some effort, but that’s organic gardening, and I wouldn’t change it for anything.
