Aphids and companion planting

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  • #14842


    I often hear things like "plant garlic by your roses to deter aphids" but does this actually work? And does it also work for milkweed aphids (Aphis nerii) or just the kind of aphids that go for rose bushes. When I google aphid+rose it seems that kind of aphid is Macrosiphum rosae?

    Likewise I’ve also been told sage repels aphids from celery, but when I google aphid+celery it seems that kind of aphid is Myzus persicae.

    Another suggestion is that aphids are repelled by the smell of marigolds. Which aphids? Which marigolds? (French Marigold, Tagetes patula; Mexican marigold, Tagetes erecta; English marigold, Calendula; Tree marigold, Tithonia diversifolia; Desert marigold, Baileya multiradiata; Corn marigold, Glebionis segetum; Marsh marigold, Caltha palustris)

    Others say sticky yellow traps are the way to go.

    It’s all very confusing to a novice gardener such as myself.

    Has anyone ever tested these aphid deterrents for effectiveness? Does anyone want to help test them?

    What I suggest is we do some research!

    (how did you know I was going to say that? ;->)

    If you know of any other supposed aphid repellents then please post them to this thread. For instance our aphid factsheet also mentions banana peel as at deterrent.

    Want to be a tester? The trick to research is to focus on the thing you are testing by eliminating as many variables as possible. So we need everything else to be the same, the only difference will be in the deterrents.

    So get 2 or more large pots or planter bags. I reckon PB8 would be a good size. That is 8 pints or 4.8L. But whatever you use make sure they are all identical. Buy a bag of potting mix and put the same amount of potting mix in each bag. This will make sure any differences are not due to the soil chemistry.

    Plant a couple of seeds in each container. Use the same sort of seeds for the whole set, eg all G.physocarpus, or all A.currassivca etc.

    Leave one pot with just the host plant. That will be your control. Then plant your chosen deterrents in the other ones. Label the pot carefully. A good way is to label the pots A,B,C and somewhere else record A= Tagetes patula, B=control, C=banana peel or whatever you use.

    Put them somewhere where they can be close to each other, but not too close. We don’t want the Tagetes patula or whatever in pot X to protect all the other pots as well. They should also be in similar conditions. We don’t want one in the shade and another in full sun for example. Finally whatever else you do to them, do it the same to all of them, eg the same amount of water etc.

    Then wait for the aphids to come calling. When they do resist the temptation to squash them or wash them off, just wait and see what happens. Finally you could ask a friend or neighbour who doesn’t know what you are testing to rate the plants in terms of aphid attack. Photos of each would be great too.

    Then post your results here. If we have a lot of testers we should be able to build up a pretty good picture of tried and true Aphis nerii deterrents.

Viewing 18 replies - 26 through 43 (of 43 total)
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  • #30864


    Yellow shouldered and Variable ladybird beetles eat Aphis nerii. I have pictures here:

    Milkweed Aphid, Aphis nerii

    However the reaction of ladybirds was described by one author as “too little, too late”. The ladybirds tend to turn up after the aphids have established a colony and then try and play catch up. Ideally what would be better is a hungry ladybird waiting for the first aphid to turn up. Which is exactly why I chose to test Coriander due to claims it attracts ladybirds because they feed on its pollen.



    Seaval years ago I used plant rua to keep aprids off my tamarillos, but rua turned to been useless as I noticed aprids on leaves of my tamarillos.

    Aprids reproduce very fast, so you need are ladybirds…red & white & black beetles…they and their larvaes eats aprids.



    Addendum: Spearmint is not a deterrent to Aphis nerii.

    In the bagged test Spearmint (Mentha spicata) did not germinate. However the seeds did germinate once the G.physocarpus had been transferred into the ground and a large colony of Spearmint plants developed around #5. However despite that it has now developed an aphid infestation.



    My friend Don is of the same opinion.



    Mary suggests that this may be how they work – by attracting the aphids they are serving as decoys?



    In my butterfly house are 10 potted marigolds as nectar sources for the butterflies, and also in the hope that they may discourage aphids. Imagine my horror today when I noticed tiny green insects on the leaves of the marigolds which turned out to be the green aphid feasting on the plants. The aphids were not only on the leaves but on the flowers as well, and to add insult to injury whitefly were present on the underside of the flower petals. So while the flowers are excellent nectar sources I will now not rely on them for aphid control.



    Brilliant stuff, Darren. I’m delighted to see this and hope it will encourage others to undertake experiments. Yours is a great example to show the schools that will be looking for ideas for projects.

    I must say that two of my plantings of milkweed support your theory:

    Spacing out G.physocarpus plants may prove to be an effective technique in aphid control. Perhaps widely spaced single plants are a less obvious target then a dense bunch of plants?

    I have no aphids (yet) on the swan plants which are almost hidden in among the Buddleias, but the plot of A. curassavica on its own is heavily infested with aphids. It will be interesting to see what happens when I return in a month.




    Seeds from a single Gomphocarpus physocarpus seedpod were germinated in Jiffy-7 peat pots. A bag of budget-type potting mix was dried and mixed for one month and then divided evenly into 8 PB8 planting bags, resulting in 2.1 Kg per bag.

    On the 28/11/2011 the peat pots were added to the PB8 bags and the bags were numbered 1-8. The bags were also surrounded by seeds of a companion plant, with the exception of 6 which was surrounded by the a banana peel and 1 which was left as a control with no companion.

    1 control (no companion)
    2 French Marigold, (Tagetes patula)
    3 Mexican marigold, (Tagetes erecta)
    4 Coriander, (Coriandrum sativum)
    5 Spearmint, (Mentha spicata)
    6 banana peel
    7 Chives (Allium schoenoprasum)
    8 Anise (Pimpinella anisum)

    The plants were then spaced out 2m apart in a straight line and left to their own devices for two months, with periodic observations. After two months most of the Gomphocarpus physocarpus plants had reached 0.6m high and their roots were observed protruding from the drainage holes of the bags, so the plants were replanted into the ground.


    At the conclusion of the experiment aphids (Aphis nerii) were observed only on plant 7, with chives as its companion plants.

    The Spearmint seeds did not germinate, so #5 became a second control plant.

    Seeds of both varieties of marigold germinated and were doing well, but then were totally destroyed and their companion Gomphocarpus physocarpus were badly damaged, losing all their leaves and about 80% of their stem. Mucus trails from snails or slugs were observed on the bags and soil.

    Plant #6 with banana peel was initially doing as well as the others, but then the top third of the stem and leaves turned brown and withered. No cause could be found.

    At this point Chives (Allium schoenoprasum) do not appear to act as an aphid deterrent.

    Marigolds seem to be particularly attractive to snails and slugs. This could be useful by planting marigolds as a “decoy” to lure snails away from G.physocarpus, but snail bait should be used when planting them in close proximity to G.physocarpus.

    Interestingly the level of aphid infestation among the spaced-out test plants was much lower than in my crowded butterfly garden about 10m away from the test site, in which nearly every plant was infested. Spacing out G.physocarpus plants may prove to be an effective technique in aphid control. Perhaps widely spaced single plants are a less obvious target then a dense bunch of plants?

    The plants have been planted along a fenceline at 1.6m intervals. The companion environment listed above will be recreated for each plant, and the experiment will continue as an in-ground test.

    Thanks to my neighbour Paul for providing the G.physocarpus seedpod, and to the trustees of the MBNZT for funding the purchase of the potting mix, Planter Bags, and companion seeds.



    I chose to test Coriander due to claims it attracts ladybirds because they feed on its pollen. However Coriander might be useful for other reasons as well.

    While Coriander (Cilantro in Spanish) is a widely used herb, a small minority of people find it extremely objectionable, (http://ihatecilantro.com) with claims that it reminds them of bugs, detergent, and other unpleasant things.

    The taste of the fresh herb is due to an essential oil (0.1%) that is almost entirely made up of aliphatic aldehydes with 10 to 16 carbon atoms. One finds both saturated (decanal) and ?,? unsaturated (trans-2-tridecenal) aldehydes (Gernot Katzer?s Spice Pages, http://www.uni-graz.at/~katzer/engl/Cori_sat.html )

    It turns out some people are sensitive to decanal, but most are not. Decanal is used in detergents and soaps, and is also used by many insects, particularly beetles, as part of their communication system (http://www.pherobase.com/database/compound/compounds-detail-10Ald.php ).

    So a decanol sensitive person comes to associate decanol with soaps, detergents, and insects. When they taste it in Coriander their brain assumes they have a mouthful of soap or bugs and triggers a strong urge to spit it out as a self-protective reaction.( http://www.nytimes.com/2010/04/14/dining/14curious.html )

    Interestingly, Decanol has also been found in grape juice contaminated with multicoloured Asian lady beetles (Ross, C. F., Rosales, M. U. and Fernandez-Plotka, V. C. (2010), Aroma profile of Niagara taint using gas chromatography/mass spectrometry/olfactometry. International Journal of Food Science & Technology, 45: 789?793. doi: 10.1111/j.1365-2621.2010.02197.x)

    Decanol is also used by some plants as a Herbivore-induced plant volatile (HIPV). When the plant is attacked by herbivores it releases HIPVs, and these HIPVs then attract predators (Poelman, E. H., Oduor, A. M. O., Broekgaarden, C., Hordijk, C. A., Jansen, J. J., Van Loon, J. J. A., Van Dam, N. M., Vet, L. E. M. and Dicke, M. (2009), Field parasitism rates of caterpillars on Brassica oleracea plants are reliably predicted by differential attraction of Cotesia parasitoids. Functional Ecology, 23: 951?962. doi: 10.1111/j.1365-2435.2009.01570.x)

    Is it possible then that Aphids might associate decanol with the presence of ladybird beetles and other predators, causing them to avoid that area?



    Yes thats a good point about measuring the plants at each assessment, and the control being a good indicator for growth rate.

    In PB’s the plants will be more likely to uptake any chemical compounds given off by their companions too. Actually it is a better control than in ground isn’t it.

    There is a lot of myth about companion planting around. Two books I have found useful are ‘Roses Love Garlic’: Companion Planting and Other Secrets of Flowers and ‘Carrots love Tomatoes’, not so much from the perspective of ‘what to plant with’ BUT what NOT to plant with, and I have found that some plants dislike being near, with, or a following crop to others.

    Tagetes has been proven in trials to repel nematodes from the soil, but is useful for many reasons:- soil building, repelling undesirable insects (yet attracting butterflies), cover cropping and weed suppression in summer on bare ground or between crops…….fantastic plant, if it reduces aphid numbers too, even a little, I’ll be thrilled.

    I’d love to know how you get on with the Banana skins. I’ve put them under roses and other flowering perennials for years knowing that their high potassium levels are likely to help with flower initiation, but hadn’t heard of them repelling aphids before. I’ll now save my banana skins for the swanplants and see how I get on with that too.



    Thank you Jennifer and Jane for the excellent feedback.

    Jennifer, rotating the bags around the locations seems a good idea, I’ll do that.

    Jane, you raise a valid point, and one that I had given some thought to. My thoughts were that I often notice aphid attack on my small seedlings before my full-grown plants. I hoped therefore that the effectiveness or not of the companion would become apparent before the bag became crowded and or nutrient depleted. I hoped the PB8 size would compensate for that, normally I grow my swanplant seedlings in PB3/4.

    Open ground trials would certainly allow more room for root development, but introduce further variables of soil chemistry and water availability which I hoped to eliminate by using bags and potting mix.

    Another option would be to grow the companion plants in adjacent bags of their own. However if the benefits of companion planting are not accepted then the mechanisms by which these claimed benefits are produced is even less certain. If the companion plant achieves a benefit by altering the soil chemistry (as Tagetes is sometimes claimed to do) then they need to be in the same bag for that effect to become apparent.

    I had a rethink having read your post, and I still think I prefer the bag option, at least for this stage. However I think I can control for crowding by measuring the height of the plants at each assessment. Since the control has no companion if the heights of the other plants remain similar to the height of the control then I think it is a reasonable assumption that the plants have not been affected by crowding. The point at which the growth of the trial plants deviate significantly from that of the control would then mark the end of the trial.

    I had also considered having clover as a companion, not for repelling aphids in itself, but I thought its nitrogen fixing may make for a healthier plant, leading to reduced appeal to pests. However I suspected that the nutrients available in the potting mix would be ample in the short term, making the clover’s contribution insignificant. But in a longer term trial in open ground the potential benefits of clover might become apparent. I’ll ponder that one for next year!

    An Integrated Pest Management strategy for Aphis nerii may well contain repellents such as Tagetes and Mentha, a predator attractor such as coriander, and a beneficial growth companion such as clover.

    But as Jackie French’s Guide to Companion Planting in Australia and New Zealand points out, “There are a lot of companion planting myths around” (http://www.jackiefrench.com/companion.html). I am just trying to introduce a bit of objectivity to my efforts to protect my plants from Aphis nerii.



    Hi Darren,

    I think you will get results that reflect the size and range of the companion plant root structure more than anything else. Tagetes patula will have smaller roots than Tagetes erecta. Mentha roots will take up a lot of room in the PB too. In the cases where the roots take up more room, they are also likely to use up more of the available plant food in the PB.
    Your G.physocarpus growth may be affected by this variable giving you results that are misleading. For example: you may find that a larger swanplant may get more aphids because it perhaps has a larger leaf surface area to infect, whereas a stunted plant due to less available nutrient)may have less aphid due to less surface area and perhaps a tougher leaf cuticle due to stunting.

    Sorry to be a critic. I think the idea is good, but the variables are great and therefore the results maybe equally inconclusive due to those variables. Open ground trials would be better because you are not confined to the small area with a PB, but would be a pain to setup and run. To gain indicative results though, I think that may be the way to go.



    May I suggest you rotate the bags from time to time to ensure each condition experiences the same environment?



    Thanks pst, I will definitely give that a go.

    I was wondering about setting up a double-blind controlled experiment by posting out coded seeds to volunteers. But banana peel just wouldn’t fit that experiment design!

    So what I’m going to do is test G.physocarpus plus the following:

    A) control (no companion)
    B) French Marigold, (Tagetes patula)
    C) Mexican marigold, (Tagetes erecta)
    D) Coriander, (Coriandrum sativum)
    E) Spearmint, (Mentha spicata)
    F) banana peel

    I will set up 6 PB8 bags, with 2m gap between them. That is about all I have space for on my front lawn. I will take weekly photographs and ask my wife to estimate aphid infestation.

    (I chose not to test basil because I already have that growing by my tomatoes. I thought Pyrethrum might repel butterflies as well as aphids. I have some coriander seeds so that will be an easy one, and I recently bought some Tagetes patula and Tagetes erecta because my wife says she likes marigolds. And spearmint will be great if it also repels ants. Plus I love spearmint but its too invasive in the garden so I’d love an excuse to grow some in a pot)



    Banana skins WORKED for all my swan plants. I had very orange stems because of the aphids and I just threw the skins under the plants and left them to do their magic. The aphids looked sick after a few days then died. I now throw banana skins under all my swan plants whenever we have some and have not had a re infection.
    Much easier than squishing them and safer than sprays.



    Hi Darren
    I use French marigolds as a nectar source and find the yellow ones are best for feeding butterflies.I am convinced that they act as a repellent for whitefly(sorry I don’t know the Latin name for our whitefly but I imagine it’s the same as your’s



    Good Idea Darren. I wish I had more room here. However I have never found companion planting works and your posting has now explained why. You are a treasure.



    http://www.gardentoad.com/companionplants.html lists the following as aphid deterrents:

    Allium–flowering onions, chives, garlic, leek, onion and shallot



    Nasturtiums (claims it both repels and acts as a trap crop for aphids. How can it do both?)


    Spearmint (repels ants and aphids)

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