32 Plants You Should Think Twice About Growing Next To Each Other

While many plants thrive together and coexist in harmony in the same garden plot, others are like oil and water. If you want a successful harvest in the vegetable patch or to grow beautiful blooms in your flower garden, it's important to know which plants you should never keep in close quarters. If you inadvertently plant certain species next to each other, you will likely end up with less than stellar results, including disease, fewer vegetables, pest issues, and more. Knowing which plants to avoid will make you a smarter, more confident gardener. So, remember to plan ahead, and don't mix sunflowers with potatoes or black walnut trees with tomatoes. 

When it comes to good and bad companion plants, look at the facts. Some plants are incompatible due to specific, easy-to-pinpoint reasons. However, some plants are considered poor companions due to anecdotal evidence. While it's always good to exercise caution, sometimes anecdotal evidence about poor companion plants may not be the reality for your gardening experiences. With that knowledge, all of the plant pairings featured here are considered incompatible based on certain characteristics, whether one of the pairs is allelopathic and produces toxins that suppress nearby plant growth or both species grow best under different conditions. Unsuitable pairings based on stories and gardening lore have been avoided for clarity.

Unfortunately for those who enjoy mixing colors and textures, hostas (Hosta spp.) are one of the plants you'll want to avoid growing with lavender in the garden. Common lavender (Lavandula angustifolia) features needle-like foliage with a light scent and spiked flowers in lilac or white. Hardy in zones 5 through 9, lavender prefers full sun. Comparatively, hostas, with their broad leaves, are hardy through zones 3 to 9 and more often than not require some shade. Many hosta cultivars actually require deep shade, which is the worst environment for lavender.

Both mustard (Brassica juncea var. crispifolia) and collard greens (Brassica oleracea var. acephala) are cool-season, leafy vegetables that like fertile soil. However, if there are not enough nutrients to go around, it will cause both to do poorly when planted together. They also both require plenty of water to sustain their leafy growth. These species also attract the same pests. It's best not to plant these closely related plants in the same bed or in an area of the garden where one has been growing in the last four years.

Be especially careful where you plant a black walnut (Juglans nigra) tree. If it's too close to your vegetable garden, you might have a big problem. An allelopathic species, black walnuts release a compound into the soil from their roots that can stunt growth in many plants. Tomatoes (Solanum lycopersicum), which are part of the solanaceous group, are especially at risk from this compound. Planting tomatoes within 50 to 80 feet of a black walnut tree is a sure way to stunt them before you ever get a harvest.

When it comes to incompatible plants, do not forget to pay attention to your flower beds. Planting certain flowers with different needs together will end badly for one of them. Butterfly weed (Asclepias tuberosa) and astilbe (Astilbe spp.) have opposite water requirements. Butterfly weed has exceptional tolerance for drought and dry conditions once it is established, thanks to a long taproot. The foliage will turn brown on astilbe plants and often go dormant if it experiences very dry soil for too long. Plus, astilbe does best in partial shade.

Although you might add cucumbers (Cucumis sativus) to a salad with tasty, aromatic herbs, you don't want to place them anywhere together in your garden. Sage (Salvia officinalis) is an especially fragrant herb with a long history of culinary use. However, alongside cucumbers, it can have a negative impact on the flavor. In addition, sage and cucumbers have incompatible water needs. The large quantity of water that cucumbers require could be too much for your sage.

Think again before you plant a border of sunflowers (Helianthus annuus) around or near your potato (Solanum tuberosum) plants. Sunflowers, while a beautiful and useful native, have an unlikely effect on many nearby vegetables. When planted next to potatoes, the plant suffers from the chemicals produced by the roots of the sunflower. Additionally, potatoes can host a certain fungus that is devastating to sunflowers.

When plotting out a landscape, consider the heights of your plants carefully. Some plants can inadvertently shade out others, like certain bush or hedge plants. The foundation yew (Taxus x media), hardy in zones 4 through 7, is an excellent example of a species that will create deep shade in your yard. A native flower like the black-eyed Susan (Rudbeckia hirta) will not tolerate very shady conditions and needs enough sunlight each day for lovely blossoms.

Pay attention to how quickly some plants grow in the garden. A fast-growing flower next to a slow-growing flower is not a good combination. For example, zinnias (Zinnia elegans) are beautiful flowers that attract pollinators and grow rapidly. Anemones (Anemone spp.), or windflowers, by comparison, are pretty wildflowers with a slow growth rate. The fast-growing flower, in this case zinnias, typically takes over well before the other plant has a chance to establish itself.

One of the plants to avoid growing next to corn at all costs is the humble tomato. Both of these delicious crops are considered heavy feeders. It is difficult to properly provide both plants with the right amount of nutrients when they are planted close together. Both veggies also share the same growing season, which means you must handle both species' nutrient needs for longer, perhaps leading to slow growth from nutrient deficiency. Next to each other in the garden, it would be hard to keep up with the fertilizer.

Planting strawberries (Fragaria x ananassa) in the same bed as your cabbage (Brassica oleracea), a member of the Brassica family, can lead to improper growth and pest infestations. These plants compete for the same nutrients, and both require consistent, deep watering for the best production. If that wasn't enough of a reason to avoid planting them together, they can attract similar pests. Cabbage loopers can easily infect both species.

Be cautious when planting Jerusalem artichokes (Helianthus tuberosus), or sunchokes, in the garden. Next to certain root vegetables, like turnips, sunchokes spread too easily and inhibit their growth. Sunchokes are not true artichokes, and the edible part grows underground. However, compared to turnips, sunchokes spread via rhizomes and can overtake a garden bed, choking out or limiting turnip growth. The tendency of sunchokes to become weedy adversely impacts the ability of turnips to get water and nutrients, too. Be sure to grow this native root vegetable in a raised bed away from turnips.

Asparagus (Asparagus officinalis) is a perennial vegetable that requires special care to grow successfully. It can take a while to see results, especially if you start them from seed, so it's best to give it the best shot possible. That means growing it far away from your onions (Allium cepa). Onions, unfortunately, can share Fusarium fungus with your asparagus. Both soil and airborne diseases can transfer, so keep them well separated.

A compound produced in the roots of the marigold (Tagetes spp.) plant might stunt the growth of other nearby plants. Although evidence is inconclusive, a Maryville College 2015 study looked at the impact of marigolds on bean plants. Instead of deterring Mexican bean beetles, the beans did not grow well. This effect might have something to do with allelopathic chemicals exuded by the roots, which are known to kill harmful nematodes. A poor harvest of beans in your garden might be in your future if you plant marigolds too close by.

Hyssop (Hyssopus officinalis), a member of the mint family, is a perennial often planted close to gardens to take advantage of its ability to attract bees and other pollinator insects. But take care if you plant radishes in your veggie patch. Hyssop tends to prevent radishes from thriving due to the chemicals it exudes into the soil.

Rue (Ruta graveolens) is the perennial herb you don't want to plant next to basil in the garden, because it will inhibit growth due to allelopathic compounds. According to a study from the Journal of Agricultural and Food Chemistry, the phytotoxins inhibit basil's growth. They also do not make sense next to each other in the garden. Rue typically wards off aphids, while basil attracts them.

Planting fragrant garlic (Allium sativum) too close to your peas (Pisum sativum) in the garden is a recipe for disaster. Garlic has allelopathic qualities, meaning it releases chemicals into the soil as it grows that inhibit growth in other plants. These chemicals also prevent natural nitrogen fixation in peas by limiting the growth of nodules. If the peas in your garden cannot fix nitrogen, then you will have stunted growth and poor yields. 

Some gardeners like to use asters (Aster spp.) in or around their vegetable gardens to attract pollinators. This flower species also attracts aphids and mites away from other plants. However, avoid planting asters near watermelon (Citrullus lanatus). Asters and watermelons are both popular foods for melon aphids. You might just end up attracting more aphids to both plants instead of trapping them. Additionally, asters are commonly affected by aster yellows, a chronic disease that could infect neighboring watermelons.

Squash, including summer squash and zucchini, are plants that need room to breathe. They do not typically take up too much space, unlike pumpkin plants with their rambling vines. However, crowding them together can lead to a tangle of vines and heavy fruit. Plus, both squash and pumpkins are susceptible to powdery mildew, so it's best to give them space for air circulation and to avoid spreading the disease.

Scented geraniums (Pelargonium spp.) can be a good companion in the vegetable garden. This bright flower can possibly deter mosquitoes and other pests. But it's important to never plant it near eggplants. Both eggplants and geraniums can be impacted by Ralstonia wilt, or southern wilt. This nasty disease can impact other veggies, too, like tomatoes and peppers.

It's best to keep your salsa ingredients apart until post-harvest time. Tomatoes and jalapeños (Capsicum annuum) go together very well, just not in the garden. The main issue is the potential transfer of bacterial leaf spot, as well as other diseases, between these two types of vegetables. Bacterial leaf spot is caused by several strains of bacteria, and many of these strains overlap, impacting both tomatoes and peppers. It can be easy for your entire vegetable garden to become infected, so put space between your jalapeños and tomatoes.

Be careful about what kind of goldenrod (Solidago spp.) you choose and where you plant it. Several species of goldenrod are aggressive spreaders and often push out other plants. For example, Canada goldenrod (Solidago canadensis) easily spreads into colonies of plants, adapting to a range of conditions. Planting these aggressive goldenrods in your flower garden can crowd out species like coneflower (Echinacea purpurea), which might not grow as tall or dense.

Pine needle rust is a fungus that spreads between two host plants, like a Scots pine (Pinus sylvestris) and aster (Aster spp.). While it doesn't cause too much harm, pine needle rust leads to discoloration in trees. For young trees, infection can slow down their growth. The easiest way to manage this fungus is to avoid planting members of the pine family with members of the aster family.

There are some incompatible plants that prevent each other's growth due to differing heights. Pole beans and beets (Beta vulgaris subsp. vulgaris) are a good example, because their height differences counteract each other. To grow large, tasty beets, you need moist soil with good spacing and plenty of sunlight. But pole beans require some type of trellis to climb and attach their vines to, which inevitably shades the beets.

Pairing shallow-rooted species together leads to too much competition for water and nutrients. An excellent example is the mismatch between rhododendron (Rhododendron spp.) with its shallow, fibrous roots and American arborvitae (Thuja occidentalis). Although rhododendron bushes grow well with some type of shade, often from a nearby tree, it's better to pair them with a tree that has far-reaching roots. Arborvitae roots tend to grow too close to the surface, negatively impacting the growth and beauty of your rhododendrons.

Dill (Anethum graveolens) is a flavorful herb you'll want to add to your garden in spring, but not next to your carrots (Daucus carota subsp. sativus). Both of these delightful garden additions are from the same family, Umbelliferae, which means that they share a lot of the same pests. While you might not automatically attract more aphids or carrot flies if you grow carrots and dill next to each other, it's more likely. Planting them together could lead to a poorer harvest.

One of the worst types of crop diseases is blight, and unfortunately, potatoes can easily become infected. Late blight impacts both potato and tomato plants, leading to a complete loss if it is not caught in time. To avoid spreading disease, do not grow potatoes near tomatoes. Blight spores can travel by wind, so it's best to give potatoes and tomatoes space. This disease infects leaves, stems, tomato fruit, and tubers, presenting as dry rot in tomatoes and shrunken, soft potato tubers.

Under no conditions should you pair lettuce (Lactuca sativa) with chrysanthemums. Lettuce enjoys cool, moist soil and shade. Mums require plenty of sun and need well-drained soil. Putting one or the other under the opposite conditions will cause harm. For example, exposing lettuce to too much full sun will result in it bolting, or flowering, which ruins its flavor. And a waterlogged mum will likely die due to root rot.

Growing wormwood (Artemisia spp.) can be a bad thing if you choose to (or unknowingly) grow an invasive variety (such as Artemisia vulgaris). Although many people have used wormwood for medicinal purposes, it can have an inhibitive effect on plant growth near it due to chemical compounds in its roots. For example, peas do not grow well next to wormwood, and it can overtake them with its vigorous growth.

While you might admire northern red oaks (Quercus rubra) and American elms (Ulmus americana) separately in your landscaping, take care to plant them apart. Although they are different types of trees and are from different genera, they both can be stricken with tubakia leaf spot. Tubakia leaf spot is a fungus that causes spots to develop on the leaves in the late summer. While oaks with pointed-lobed leaves are the main ones impacted, it can also show up in elms.

Fennel (Foeniculum vulgare) and cilantro (Coriandrum sativum) are two herbs you'll want to avoid growing too close together in the garden. For one thing, cilantro and other members of the same family can inhibit fennel seed production. However, the main reason to keep them apart is the harm that fennel can do to this herb. As an allelopathic plant, fennel prevents growth and sometimes encourages nearby plants to bolt.

When planted too close together, fruit trees like apple and peach alongside mint (Mentha spp.) are a troublesome combo. Mint, including common peppermint (Mentha x piperita) and spearmint (Mentha spicata), habitually overtakes areas with its fast, rhizomatic spread. If you choose to plant mint at the base of your fruit trees, you run the risk of creating competition for resources between the two root systems. The roots of mint plants are reaching and spreading, but fruit tree roots are shallow (typically found in the top 6 to 24 inches of soil).

While you might love the classic beauty of roses (Rosa spp.) and the whimsical nature of hydrangeas (Hydrangea spp.), they might not work well together in the same flower bed. These two beautiful shrubs have conflicting needs that make them incompatible. Hydrangeas require more shade than most rose bushes, especially in hotter areas. Plus, the roots of roses do not grow well near other shrubs. It's recommended to plant them far away from competing shrubs, including hydrangeas.