Can’t Figure Out Why All those Nasty Bugs are Feasting on Your Cabbage Plants?

Pest control can be tricky in an organic garden. You know you want the best quality food for your family but choosing not to use chemical pesticides means you may see more bugs in your vegetable garden. Opting for raised garden beds can help to reduce the number of hungry pests you have to cope with. But ultimately, you will need to have a plan for insect control or insect removal to keep your organic vegetables safe from all that munching.

Many organic gardeners look to companion plants that repel insects from the vegetable patch. Many of these are strong-smelling herbs and flowers such as chervil, rue, or marigolds. You may also have read that companion plants like nasturtiums both repel harmful insects and attract beneficial pollinators such as bees, butterflies, and even hummingbirds to the garden. Based on claims like this, many gardeners grow nasturtiums in their container gardens and use them as edging plants in their vegetable gardens.

Are your nasturtiums attracting bugs that eat your cabbage plants?
Nasturtiums are edible flowers that are often used to repel insect pests and attract pollinators to a garden
(Image: zrenate/Pixabay/CC0 1.0)

What? The Bugs are Eating the Nasturtiums?

I recently wrote a Facebook post highlighting the use of nasturtiums as a companion plant. The post published on the 24 Carrot Diet page and I then shared it on my personal profile. Within minutes, I received two responses talking about bugs and nasturtiums.

The first comment came from a neighbour who is starting a home-based greenhouse business. He mentioned that last summer he found small black beetles (maybe flea beetles?) were attracted to his nasturtiums. These same bugs also had a particular affinity for plants in the brassica, or cabbage, family. He said he was glad he had put the nasturtiums into his flower beds, and not in his vegetable garden as he’d been planning on doing.

Another friend from back East mentioned that the area of her garden that was bordered by nasturtiums has been devastated by slugs, another pest that likes to eat members of the cabbage family (among other things.)

Until that moment, I had never questioned claims that nasturtiums repel garden pests. The pungent smell of the leaves and flowers is supposed to keep many insects away, just as the smell of a marigold would. And since I had never had trouble with any insects in my nasturtium plants, I always believed that to be true.

Well, it turns out that I only had half the story . . .

Yes, some insects do find the smell of nasturtiums unpleasant. But it turns out that nasturtiums do have natural predators. According to Burpee, nasturtiums fall prey to aphids, cabbage looper, leafhoppers, leafminers, and slugs. If you noticed that a lot of these yard pests also like to feast on brassicas, you are right. And that’s because nasturtiums are related to brassicas.

Now that’s something I’ll bet you didn’t know!

Nasturtiums are Related to Brassicas

I didn’t make the connection between nasturtiums and the bugs my friends were talking about until I did a little bit of digging – online, not in the garden this time. It took me a moment since nasturtium is not in the same genus as cabbage and its various cultivars: broccoli, kale, collards, cauliflower, and kohlrabi among them. It isn’t even in the same family as the cabbage, the Brassicaceae which include many other brassicas besides the cabbage cultivars: rutabagas, turnips, mustard and cress, and seed crops such as rapeseed and canola that are used to make oil.

But the nasturtium, Tropaeolum majus, is a member of a larger order of plants that includes the Brassicaceae. It’s called Brassicales and its almost twenty constituent families include other familiar plants such as capers, horseradish and papaya. They also include the family Tropaeolaceae, of which the genus Tropaeolum is the sole member.

And that would seem to make nasturtiums and cabbages something like distant cousins!

Could a Popular Companion Plant be Attracting Yard Pests to Your Cabbage Patch? | Garden pest control DIY | Organic vegetable garden | Heirloom gardening
Can companion plants like nasturtium actual attract insect pests to your vegetable garden?
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Graphic made in Canva using a public domain image by Pixabay user wilhei

Will Nasturtiums Attract Insect Pests to Your Garden?

So, does growing nasturtiums in your yard bring insect predators to your vegetable garden? That’s probably a question for a master gardener. As I said, I’ve never had problems with insects attacking my nasturtiums. So I have no personal experience to draw on in answering that specific question. What I can say is that it’s best to experiment a bit and see what happens in your own garden.

But we did have a related experience this summer, with our tomato plants and some cosmos that my daughter decided to plant in the raised bed with them. It was a really hot, dry summer in British Columbia this year. Our tomato plants were getting a bit dry and, apparently, this attracted some whitefly and aphids to the garden. We found a few of these sap sucking insects on the tomato plants. But most of them went to the cosmos. In fact, we found ants farming the aphids all up the stem of several cosmos.

Cosmos used as a trap plant for aphids
Ants farming aphids on a cosmos stem


If anything, the cosmos lured the aphids away from our tomatoes and other vegetables. There were very few aphids on the tomatoes, as you can see from the photo below. When we realized this was happening, we chose to sacrifice the cosmos blooms in order to get rid of the large number of insects in the garden. We cut the cosmos off below the point where the insects were gathering, and we immediately removed it from the garden. So, the cosmos had become an accidental trap plant that protected our tomato crop this summer. Next year, we plant to try interplanting more cosmos with our tomatoes for this very reason.

Our tomato plants were protectetd by the cosmos which lured aphids away
Very few aphids could be found on the tomatoes as most were on the cosmos

Using Nasturtiums as a Trap Crop

One thing you may want to try if you’re overrun with pests that attack your brassica plants is to use nasturtiums as a trap crop. Try to time the planting so your nasturtium will be blooming right around the time that you normally see the yard pest that you want to target. For example, if aphids are an issue in your organic vegetable garden during May and June, this is when you need your nasturtiums to be their most attractive.

Plant them close to your brassicas so the aphids will go to them instead of your developing broccoli and Brussels sprouts. Then watch the nasturtium plants for signs of an aphid infestation. You want to cut back the affected growth and take it well away from your garden, removing the aphids with it. This will help remove some of the pests from your garden. And not to worry, nasturtiums do grow back after being pruned!

Gardening is not an exact science so you’ll have to play around a little with the timing, placement, and number of nasturtiums you plant. Depending on how many insects invade your garden, you may want to plant nasturtiums right next to your brassicas and other vulnerable crops. This is called interplanting. (And of course, if you were wanting to harvest the nasturtium leaves or the plant’s edible flowers, you’ll want to have another planting elsewhere in your yard, where it’s less likely to be eaten by the bugs!)

As I said in my introduction, do it yourself pest control can take a little working out. Then again, starting a home vegetable garden or maintaining an existing garden has to be viewed as an investment in your family’s health. Growing your own vegetables organically is one of the best ways you can be sure you’re putting healthy food on the table every day. So don’t be discouraged if it takes time to learn which pests you’re dealing with and to become familiar with their habits. Eventually, you’ll have all kinds of strategies for yard pest control – and for enjoying those lovely nasturtiums alongside their brassica cousins!



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Original content © 2017 Kyla Matton Osborne, aka #RubyWriter
Last updated 08/09/2017

This article was published on my food blog, 24 Carrot Diet. If you are reading this content anywhere else, it has probably been stolen. Please report it to me so I can address any copyright infringements. Thank you!