Plants You Should Never Plant Together

Most gardeners have heard of companion planting, or planting certain crops together because they’re mutually beneficial. Much of companion planting is based on observation and folklore, though preliminary research shows there may be some truth behind this long-held practice. A few studies have shown limited effects, such as planting African marigolds near your tomatoes to use as a trap crop for pests such as aphids or basil to help tomatoes grow more vigorously.

Another aspect of companion planting says some plants shouldn’t be planted together. While there have been few studies proving certain plants don’t “like” each other, plants sometimes do fare better if not planted together. That’s especially true if these plants will need to battle it out for water and nutrients, or if they both attract similar pests or diseases that could wipe out both crops, for example.

While nothing is foolproof, it certainly won’t hurt to experiment with companion planting principles in your own back yard. Because every garden is different with its own microclimate, nutrient needs, and weather conditions, you’ll need to pay attention to your individual results to determine what works best.

Ahead, here are a few suggestions for plants that should not be planted together:

Tomatoes and Corn

Tomatoes and corn attract the same pests, such as tomato fruitworm, so both crops could be wiped out by these insects if you have an invasion.

Cucumbers and Potatoes

These plants compete for the same types of nutrients, so it’s better to give each of them their own spaces. They also can both be infected by cucumber mosaic virus, which has no chemical controls.

Black Walnut Trees and Most Other Plants

Black walnut trees (Juglans nigra) contain the chemical juglone, which kills plant roots to reduce competition. Once it’s released into the soil, this chemical can damage annuals, garden vegetables, fruit trees and some perennials. If you have a black walnut on your property, don’t expect to grow a garden nearby because vegetables such as tomatoes and peppers are especially vulnerable. Grasses, however, seem to do fine.

Tomatoes and Eggplants

Tomatoes and eggplants both attract hornworms. Planting them too close together offers a buffet to these pests, resulting in the potential loss of both crops.

Garlic and Onions

Garlic is susceptible to most onion diseases, such as powdery mildew. Give them both a fighting chance, and don’t plant them too close to each other or in the same spot year after year.

Cabbage and Other Cruciferous Vegetables

Cabbage and other cruciferous vegetables such as broccoli, collards, kale and mustard greens are subject to injury by cabbage loopers. Some gardeners report that planting a large number of cruciferous vegetables together seems to attract more of these pests. A more diverse planting may reduce the risk that you’ll lose everything if these unwelcome insects come calling.