5 Plants You Should Never Grow Around Peppers

Peppers are a great beginner vegetable to grow because they’re hardy, drought-resistant, and prolific, making for a hands-off, rewarding crop. If you’re looking to maximize your harvest, companion planting is a great way to capitalize on natural symbiosis, but you’ll need to pick the right plants first.

Companion planting is about either covering up a weakness or cultivating a stronger environment for your crop to thrive in. Peppers have a ton of options, from marigolds and basil that ward off pests, to nearby millet that can attract pests that would otherwise eat away at your more valued plants. They even provide their own value, depending on the type you grow, like how cayenne keeps unwanted guests out of your garden, securing a good environment for your other veggies. But some plants go beyond useless for peppers and may actually end up harming them in the long run.

For all the ways a companion plant can help your peppers, the wrong choices have an effectively infinite number of ways to harm them. From disease, nutrition theft, crowding, and attracting the wrong pests, they can sabotage your carefully cultivated environment in some brutal ways.

You may have heard the phrase “fennel has no friends” for good reason. In the evolutionary arms race of plants trying to one-up each other, fennel found a particularly nasty chemical weapon that’s profoundly effective against peppers.

Fennel produces allelopathic chemicals, a fancy term for a compound that suppresses the germination, development, and growth of pretty much anything that isn’t the same species. It’s not the only species that does this — black walnut trees are notoriously difficult to plant around. However, they’re still part of a thriving environment because native plants have had centuries to develop immunity to their particular chemicals. While this isn’t a toxin that affects humans, it’s a fairly potent herbicide for most of your vegetable garden.

Peppers are a solanaceous plant, which are all a bit sensitive to chemical changes like soil pH imbalances. This makes them particularly prone to “fennel poisoning,” and they end up with yellowing leaves, stunted stems, and smaller fruits. Even if you introduce a fairly mature plant to a fennel-rich environment, it likely won’t live for long or produce much of a crop.

Planting too close together is one of the most common beginner gardener mistakes, but it’s not limited to just your annuals and crops. Some plants spread so aggressively that they should never be planted in-ground, and there are few more aggressive than anything in the mint family.

The same things that make mint perfect for beginner gardeners make it dangerous for peppers. It spreads both above ground through seeds and below ground through rhizomes, a type of bulb that grows off of roots to produce a new plant. Additionally, it’s extremely hardy, capable of surviving in all sorts of soil, sun, and water conditions. Most gardeners avoid planting it in-ground at all; once it’s there, it’s impossible to get rid of.

While your okra, tomatoes, and pumpkins may not care much because they have such deep roots, your peppers certainly will. As another shallow-rooted plant, your peppers will end up competing with mint for nutrients and water. Plus, aggressively spreading mint makes it harder for your peppers to develop their root system, introducing an unnecessary obstacle to their growth. While a large, mature pepper plant might be able to stand up to the incursion, a small seedling will quickly become swamped and likely die off quickly.

Given that plants in the same family have many of the same nutrients, sun, and water requirements, it would make sense to have a little family reunion in your garden. However, not only is it a bad idea to plant similar plants too close together, but it’s especially bad for nightshades, like tomatoes, potatoes, eggplants, and peppers.

Nightshades are particularly prone to diseases and pests. This is partially why companion plants for your tomatoes are so important, as they need every advantage they can get to grow the best fruit. While planting nightshades together doesn’t necessarily increase the risk of disease in your garden, it means that if one plant gets it, the ones nearby most definitely will.

Some problems are more manageable than others. The same family of plants might compete for nutrients, but this is easily rectified with regular fertilizing. Some pests, like tomato hornworms, are fairly easy to spot, especially with a UV light, and can simply be plucked off and squished. For something like tobacco mosaic virus, however, it can wipe out your whole crop of nightshades since there’s no cure. No matter how diligently you till, fertilize, and water, failing to control disease and pest vectors can swiftly destroy all your peppers.

Outside of the confines of your garden, root vegetables are great trap crops, low-effort plants that attract the pests that may destroy your more valued garden residents. However, planting them anywhere near your peppers is a recipe for disaster, as harvesting them can be quite disruptive.

As previously mentioned, peppers have shallow roots, typically only a foot or two deep. However, they also spread relatively wide, requiring at least 18 inches of space between them. Roots of the same plant variety can intertwine and coexist well together without harming each other, but this isn’t true of other species. Root vegetables don’t have a very flexible structure, and this can quickly crowd your shallow-rooted plants.

But the biggest danger comes from harvesting things like potatoes, carrots, and turnips. They require some amount of digging and pulling, which agitates the soil. All this movement can disrupt the earth around pepper plants, potentially damaging their roots. While a large, mature plant can stand up to a bit of this, younger, more sensitive plants may end up dying since they can’t absorb water and nutrients correctly.

Brassica plants are nutritious, delicious, and easy to grow, making them a staple in many gardens. However, you might want to consider keeping them away from peppers since they have their own prime growing conditions and even a potent chemical defense mechanism that peppers hate.

Most brassicas, such as cauliflower, kale, lettuce, and broccoli, are cool-weather plants that thrive when temperatures don’t exceed 70 degrees Fahrenheit. This is the opposite of peppers, whose minimum is 70 degrees Fahrenheit, but they can thrive in even higher temperatures. Plus, brassicas like a more neutral soil pH than the acidic soil pH that peppers love, so you’ll find it challenging to prepare a garden suitable for both. Plus, without heavy fertilization, you’ll find your brassicas like to steal nutrients away from your peppers, leaving neither plant happy.

But the biggest reason to never mix the two is that brassicas attract a ton of pests that peppers hate, such as flea beetles and cabbage worms, which eat holes in leaves. Brassicas tend to hold up to this damage a bit better than most plants, but peppers aren’t able to regenerate their leaves in the same way. Plus, brassicas produce glucosinolates, a potent chemical defense system against herbivorous pests. While it can harm pepper plants, the biggest issue is attracting pests, only for them to realize there are easier pickings nearby.