Hello! I keep reading that the planting of alliums alongside roses can reduce blackspot. Is this just a rumour that’s got out of hand or do any of you know of any conclusive evidence?
Hello James_D!
I haven’t tried this recipe myself in this case, but the attached scientific paper proves your thesis because this study shows, that Allium is at least on the second place in the ranking after Neem oil, which could probably show phytotoxic effects.Therefore Allium is best recommended for organic farming. I’m sure it’s worth a try.
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This is in applying a solution which has allium in it? I’m reading people just planting it around roses to help with black spot. Which would be nice, get a flower and reduce blackspot at the same time
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I’d imagine you would have to apply a solution containing the allium to reduce the black spot. Simply planting them with the roses would have so little effect on the actual rose tissue or the air surrounding both plants, I can’t see how they could have any effect. It’s probably as effective as the wives tale stating planting marigolds around your roses prevent spider mites and Society Garlic prevents snails. The marigolds were SMOTHERED in spider mites and their webs which quickly moved over to everything else and were only eradicated when the marigolds went into the trash and I bought a water wand and began using it. The Society Garlic was THE favored hide out of all the brown snails. Kind of perverse if you think about it. Garlic with snail… If I wanted to thin the herd, all I had to do was comb through the garlic and smash them on the street.
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My thoughts also! Many old wives tales in Britain when it comes to gardening. This one baffles me as it’s on the royal horticulture society and gardeners world websites! It makes more sense that an application would prevent black spot. It’s an odd one as other than that article above, I have seen no evidence and so many places pushing this nonsense… I guess I wish magic was real!
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Don’t we all? LOL! It would make many things SO much easier and probably more fun!
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I plant Allium (sativa → garlic) next to my roses to keep away ants that put aphids on my roses. I’ve noticed in the meantime that it doesn’t keep the ants away, but I imagine there would be a lot more ants with aphids if I didn’t plant them 
The garlic benefits from the fertilizer I give my roses and in summer and autumn I occasionally pick some fresh garlic. It’s more of a convenience than a solution.
I cannot believe planting garlic would reduce blackspot. What is true about garlic and Allium in general is that those plants contain more sulphur than other plants. So maybe in fall, when the infected leaves fall to the ground and mingle with the leaves of the Allium, the sulphur released when the Allium foliage decomposes affects the spores or the black spot fungus. Sulphur is used to reduce fungus on many types of plants. But that is just an idea that just popped up. So no scientific data on it what so ever. I’m really sceptic about the benefits of Allium planted alongside roses to keep blackspot away. You can’t fight it.
Plant and breed healthy roses. Put them in a spot they like. Feed them, water them. Don’t keep the diseased ones.
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I’m of the feeling that you breed healthy roses put them in the right place, water, feed and then try all magic possible that’s not chemicals to make them shine
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The latest I hear is that Cracked corn being spread around your roses in spring before getting fed will help reduce blackspot due to drainage and the introduction of a beneficial fungie. Anyone given it a go before?
Sorry, latecomer to the allium topic…
I’m sure you have heard of companion planting, I read or heard just lately that alliums are the opposite of a companion plant - most plants don’t like them. Certainly with chives, considering root systems alone, they are vigourous and dense which I would view as competing for garden goodies. (My chives and russian garlics have been relocated away from the trial with BS & roses.)
I remember scattering cornmeal (made from maize, I should add) around my roses years ago for the same supposed reason, plus weed reduction, if I remember right–it didn’t make any noticeable difference in blackspot incidence as far as I could tell. You might be helping to feed certain beneficial soil fungi and perhaps other microbes by doing that, even if it doesn’t change the blackspot situation much. Still, even if you take the soil out of the equation entirely, blackspot spores will overwinter on roses’ canes and leaves unless they are either removed (leaves) or directly treated (canes). On top of that, if you use coarsely cracked corn (maize), you might also attract unwanted attention from other unwanted mammals until it has rotted to the point that it has lost its food value.
Having seen various Allium species being directly attacked by aphids, I doubt that even a fresh garlic necklace could protect roses from those little vampires. Most of the time, a strong spray of water or squashing them by hand (unless you are spiritually disinclined) is the best way to deal with them on a temporary basis when their numbers get out of hand.
Breeding and selecting roses for blackspot resistance is the only sustainable answer to that problem. As far as I’m concerned, the only realistic solution for aphids is attracting and retaining beneficial predators to the garden or landscape by fostering curated biological diversity. It’s perfectly normal to see a surge of aphids on roses’ new growth in the spring, but after that, they usually diminish to the point of near invisibility in a functioning garden ecosystem.
Stefan
I used to breed escargots as a hobby for a few years. They, and many other snails and slugs, love cornmeal. It is powerfeed for snails. I would not recommend to disperse it around young roses.
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