Discover which vegetable, herb and flower combinations not to plant for a beautiful and productive garden. Several years ago, as I planted my tomatoes and other crops for the summer season, I saw little sunflowers popping up amid and around the young transplants. I thought it was such a nice mix so inter-planted them.

However, as those sunflowers bloomed in early summer, they edged out the tomatoes that also required sunlight. Additionally, the birds left behind seed hulls that impacted the local soil. And I have learned that some plants are better off separated. My expertise comes mostly from hands-on experience in the garden and testing out new things that I can pass along to others.

What Makes Plants Incompatible?

In the case of warrior tomato.plants and frail sunflowers I did not anticipate the speed with which Sunflower seedlings would zoom ahead, reach for the sky and eventually create a shade ceiling above them, nor did I expect warrior tomatoes to surrender after growing half a foot in the intervening week. I had no idea the hulls of the seeds that I sprayed would contain chemicals that would kill other plants (allelopathy). Those are two separate reasons why plants grow poorly near each other. Factors to also take into account include similar water and nutrient preferences of the two plants, and those such as another type of garden pest that may affect both.

Vegetables Not to Plant Together

Although we view our veg patch as like one big happy family, there are some that simply prefer to be spaced out a bit from their nearest and dearest. Your garden will be a much happier place once we learn how to best develop plant relationships.

1. Cucumber and Squash

Since cucumbers and squash are families, they also require fertile mineral soil to live. You can even grow multiple species side-by-side, as long as they do not have the same nutrients demands – planting cucumbers and squash together will make them compete for the basic resources and deplete their soil.

2. Lettuce and Celery

Celery will bring pests, like aphids and whiteflies which can lead to an infestation of lettuce as well, it is a no go.

3. Fennel and Tomatoes

Most garden vegetables just do not pair well with fennel, and tomatoes are particularly affected. Avoid planting fennel near most other vegetables. So grow it in a pot, away from the other plants!!

4. Corn and Tomatoes

Corn and tomatoes should not be planted together as corn is a tall gangly plant, tomatoes are short sprawly plants. These two plants are heavy feeders so make sure to provide them with nutrient rich soil. Planting together also creates competition for major nutrients, and will retard growth of both types. In addition, tomatoes grow best in full sun and a forest of tall corn stalks can shade small tomato plants.

5. Kale and cabbage

Kale and cabbage shouldn’t be planted together as it will leach, unable to replenish or provide additional nutrients. It is not good to plant the same families of vegetables in the same garden spot year after year, she explains. This practice, however, draws nutrients from the soil.

6. Potatoes and eggplant

Make a list of what pests prefer to prey on what plants. For example, do not plant potatoes and eggplants immediately next to each other because that potato beetle also likes to feast on the flowers of eggplants.

7. Carrots and bush beans

Carrots have tiny ferny tops and bush bean’s wide leaves will provide shade to them, consequently you would not see carrots thriving. Don’t crowd, or they won’t develop properly.

8. Broccoli and cole crops

Broccoli is good for humans but it does secrete root exudates that are meant to deter pests, and the chemicals can impact the growth of other cole crops (a general term for broccoli family members). Keep broccoli away from cabbage, kale, cauliflower and Brussels sprouts.

9. Tomatoes and potatoes

The sound of blight falling on the ears of a gardener is like nails on a chalkboard as gardens that bristled with promise wither under a fungal attack. Since tomatoes and potatoes belong to the same botanical family, they may suffer many common infections. So space it out between them.

10. Onions and beans 

It was claimed that onions inhibit bush bean growth. What I should say instead is, they have incompatible watering requirements. Although both do best with plenty of water early on, after the onion tops have matured and fallen over, most gardeners will stop further watering to let them cure. Beans, on the other hand, like to be watered regularly for most of the year.

Herbs Not to Plant Together

Many herbs grow well together so you can plant several different varieties in the same pot, but some are better suited to separate pots or not right next to each other. Some herbs, such as mint, are considered bullies by most gardeners. Others give out chemicals to inhibit the growth of other plants near them.

1. Mint and Any Other Herb

First of all, mint is probably the best herb to have even been planted in your garden. It smells super delicious and tastes amazing as a garnish in a cocktail. And it may sadly improve a dull glass of water too! Therefore you might really want to plant it. But, this herb is really very important to plant alone.

But mint is quite the aggressive grower, warns Lindsay Etemadipour, holistic herbalist and founder of Symbi, a women-owned and operated small-batch tea shop. Therefore, yes you get too much of a good thing. To rein in its tendency to wander, she suggests growing mint in a pot all on its own.

Tips

You should never even grow mint close to mint. If you plant sweet and peppermint in close proximity, for example, they will cross-pollinate and over time neither species will have the characteristic scent of flavor it should.

2. Dill and Lavender, Marjoram, Sage, or Parsley

A little bit of dill in your soup or even just over top of a bagel with some cream cheese? Yummm! You still want to isolate it, but you do not have a plant in complete isolation. Dill should be planted at a distance from a variety of herbs, including lavender, marjoram, sage and parsley. Unfortunately, dill beckons horrible scum of the earth bugs that literally eat and kill all your herbs. Dill also prefers moist soil, and the herbs I’ve mentioned above prefer dry conditions.

3. Sage and Chives

In chicken or fish, sage might add a more subtle, flavorful profile. On the other hand, it is better to keep it away from chives as sage favors a drier soil than the wetter chive. It is best to cultivate this herb close to thyme. TWO of our expert gardeners pick two great perennials, sage and thyme which grow well in dry, well-drained soil in full sun. I plant these together because the strong scent of sage also keeps pests off oregano.

4. Basil and Sage

Basil is an all-around recipe enhancer so what other herb should you plant? But, plant them away from sage, experts advise. But Etemadipour suggests planting basil with oregano or parsley instead. I like to plant basil, parsley, and oregano together as basil is a fantastic repellent for some of the insects that will target your oregano and parsley. The two herbs grow under similar conditions of a lot of sun, and well-drained soil, so they are also one at the end of things.

5. Fennel and Any Other Herb

Fennel does not get enough credit as an herb. Fantastic in salads and stews, it is a homegrown favorite. Much like mint. I recommend isolating by planting. This should be noted because, unlike mint, it does not spread like an invasive plant… but instead releases the same chemical that can make things like other herbs or the vegetables you planted slow to grow. Plant foraging fennel elsewhere

“Fennel is persnickety and appears to inhibit growth in many neighboring plants and also seems to want to take over the garden.

6. Mint and basil

You do not want to put something that spreads quickly next to one that grows very slowly. A year later, I pushed a couple of basil shrubs into what appeared to be empty space. Later in the summer, chocolate mint tried to take over and just about smothered my basil.

7. Fennel and cilantro

Fennel falls somewhere between a vegetable and herb in essence, and we are claiming it as an herb for our purposes here. Fennel exudes chemicals that will prevent the germination of seeds so keep it separated from cilantro and other seed-started plants.

8. Sage and lemon balm

These two herbs are aromatic in their own right, with great applications in the kitchen. This means as you are providing for the water needs of the lemon balm, you are also watering it too much. Store your sage together with other herbs and flowers which prefer the dry, just like, violet, lavender.

Flowers Not to Plant Together

1. Geraniums and Impatiens

Oftentimes we focus on colors, flower shapes or even height when selecting flower combinations and neglect the growing needs of each plant. I often see this combo using white impatiens and red geraniums for the color combination. It is too short a life of design! Impatiens love shade, but geraniums need sun. Sun for the impatiens and shade for the geraniums. Which one grows better in the garden and which fails depends on how much sun they get.

2. Japanese Spiraea and Roses

Using shrubs and roses to provide height and dimension in the garden beds is great, but be practical when you plant your roses with other woody plants. A shrub, such as the Japanese spiraea, bears small lovely flowers in clusters in addition to the quite aggressive root system which could probably harm your roses. Aggressive root systems that will compete with other plants for water and nutrients are typical of fast-growing shrubs. They also get so large that without them being hard pruned routinely, they begin to shade out my roses that love a ton of sun.

3. Petunias and Rex Begonias

The trumpet shaped blooms of petunias come in so many different colors and can be a delightful addition to any flower bed, border, or container. Rex begonias; they have neat foliage–sometimes magenta or purple leaves and sometimes green and purplesplatters. Of course, petunias want the sun and rex begonias like shade, so attractive as they are together (you could carry in your container), those two should not receive adjacent planting. Note that if you planted it in the right sunlight spots, they will grow properly. Don’t forget to read the plant tag and make sure that each plant you love has room!

4. BALDOMIR/GETTY IMAGES

Limiting: We typically integrate sun-loving flowers together and shade-loving flowers together. Some have other issues: aggressiveness, pests that prefer them as hosts, etc.

5. Black-eyed Susan vine and bachelor buttons

Each of these flowers is a garden favorite in its own right. The black-eyed Susan vine, planted too close to comfort with the almighty bachelor button, twines itself through and around stems until it covers the bachelors.

6. Sunflowers and Potatoes

For example, you may want to plant those mustard yellow or reddish-orange blooming sunflowers intended to attract more pollinators when it comes to your vegetable garden, but not all vegetables are okay with others living there – like potatoes and sunflowers.

A second point is that sunflowers have very big root systems, and since they grow very tall (depending on the variety) they may also cast too much shade for the potato plant. Sunflowers are also allelopathic, meaning they have certain toxins that can be fatal to other plants. Sunflowers growth inhibition of surrounding plants, including potatoes.

7. Asters and zinnias

I’m having problems with blister beetles on my aster plants! With that in mind, it is a good idea to separate asters or zinnias from the species preferred by blister beetles. However, lumping your pest-conscious selections together there, you are essentially building a buffet for it. This way the ravenous blister beetles can wipe out two species of flowers rather than just one.

8. Daylilies and gladiolus

Simulations for daylilies and gladiolus are available in Fig 4.Fig 5. Both daylilies and gladiolus make a stunning bouquet, but both are also quite prone to thrips (a tiny sucking insect ). Small pests can run amok and destroy these beautiful blooms when grown together in the garden. Provide some space so if you see thrip damage on one of the flowers, it may not affect the other.

Other Plants Not to Plant Together¹

Roses and hops

Hop is the best perennial to grow against a fence because it turns into, well, a climber again every season. In the fall or spring, these are also quick to clean up to prepare for new growth. Just don;t put roses anywhere it crosses with hops blossom, really-it may also grow through new in a single day into a date rosebush.

Black walnut trees and anything

Black walnut trees are infamous for causing many of your desired garden plants to fail to thrive simply because they have grown in their immediate vicinity. Garden new beds at least 50 feet away from the tree if you have a black walnut in your landscape.

Nasturtiums and eggplants

Flea beetles are common pests in most vegetable gardens. Over two growing seasons, Bundi had a problem she blamed on flea beetles with her nasturtiums. Flea beetles hop from plant to plant, so be sure to separate nasturtiums and eggplant-another beloved meal for flea beetles.

FAQs

What is companion planting?

The history of companion planting is laced with lore and established as an unscientific practice that combines the chemical properties of a given plant, coupled with how its neighbors might affect its growth or vulnerability to pests. The companion planting methods of pairing up “friendly” plants that flourish grown together, or at the practices may be more anecdotal than anything, but some gardeners swear by them.

Companion planting is not an exact science but knowing the reasons why some plants should not be planted together can help us decide what is best for each area of your garden.

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