9 Bad Companions for Eggplants (Compatibility Alert)

Imagine stepping into your garden, only to find your eggplants struggling while their neighboring plants flourish. This is a consequence of mismatched companion planting.

Eggplants struggle when planted together with nightshades (e.g. tomatoes, potatoes), brassicas (e.g. broccoli, cabbage), squash, cucumbers, asparagus, fennel, and corn due to incompatible soil requirements, nutrient competition, shared pests, and chemical inhibition.

In this article, we’ll find out the reasons why eggplants would rather not share a bed with these plants.

Let’s get started!

What makes a bad companion plant for eggplants

Soil compatibility

The first factor to consider is soil compatibility. Different plants have different soil requirements, including pH levels, nutrient composition, and moisture levels.

Eggplants prefer a slightly acidic pH (between 5.5 and 7.0) and well-draining soil rich in organic matter.  Plants that thrive in alkaline soils and different soil conditions might not make a good pair with eggplants.

Nutrient requirement

Understanding the nutrient requirements of plants is important in companion planting.

Grouping plants with high nutrient requirements together can create competition among the plants, and the stronger, more aggressive plants may outcompete their companions, leading to the deprivation of essential resources. This can result in stunted growth, reduced vigor, and overall weakened health for the plants that are unable to access sufficient nutrients.

Eggplants are heavy feeders and need a good supply of nitrogen, phosphorus, and potassium.  Plants that also heavily feed on these nutrients could starve eggplants and hinder their growth and fruit production.

Root depth

The root depth of plants is also a factor to consider in preventing nutrient competition in companion planting.

The root depth of plants determines the extent to which they can access nutrients in the soil. Plants with shallow root systems primarily rely on surface nutrients, while those with deep root systems can access nutrients from deeper soil layers.

Eggplants have a rather deep root system that can reach a depth of 18-24 inches (45-61 cm) under optimal conditions. 

When plants with deep roots are planted close to eggplants, they may compete for limited nutrients because they have overlapping root zones in the soil. This competition can potentially lead to nutrient deficiencies in both plants if the available resources are not sufficient to meet their needs.

Pest and disease susceptibility

Plants from the same nightshade (Solanaceae) family as eggplants often attract similar pests and are susceptible to similar diseases.

Therefore, planting these together could potentially lead to a higher concentration of pests and disease spread, negatively affecting yield.

Chemical inhibition

Some plants release chemicals that can inhibit the growth of other plants, a phenomenon known as allelopathy.  

These chemicals are called allelochemicals and can be released through various parts of the plant, such as the roots, leaves, stems, or even the decomposing plant material.  Such plants would make a bad choice In companion planting.

Now, let’s take a look at the plants that are not ideal companions for eggplants.  Some of these plants have more than one of the factors mentioned above.

Bad companion plants for eggplants

1. Tomato

Eggplants and tomatoes are both members of the nightshade (Solanaceae) family. This means they have similar growth habits, nutrient needs, and root structures.

Many tomato plants also have deep roots that extend about 24-36 inches (60-90 cm) deep into the soil, which is also where the taproots of eggplants extend to.

Since they share similar root zones, if they are planted too close together, their roots can come into contact with each other in the soil. When this happens, they can compete for the same water and nutrient resources. This competition can potentially lead to slower growth and lower yields for both plants, as they might not get the amount of water and nutrients they need to thrive.

Also, being part of the nightshade family also means that the plants can attract the same pests and diseases when planted side by side.

The tomato yellow leaf curl virus which is primarily associated with tomatoes can also spread to eggplants.

2. Potato

Despite being in the same nightshade family as eggplants, potatoes, and tomatoes are not considered good companions.

These plants are susceptible to many of the same diseases and pests, such as the Colorado potato beetle and verticillium wilt.

The pest is difficult to control, as it’s resistant to most pesticides and the combination of potato and another nightshade like eggplants drastically increases the chances of an infestation and will also increase the size of the infestation since both crops are a potential food source.

Planting potatoes and eggplants together can also increase the risk of these problems spreading rapidly among the crops, negatively impacting yield and plant health.

3. Cucumber

Cucumbers and eggplants are not ideal companions because of several reasons.

First, both cucumbers and eggplants require a significant amount of nutrients, they could compete for resources if planted closely together.

Second, cucumbers are typically vining plants, while eggplants are bushy. The vigorous growth habit of cucumbers could potentially overshadow eggplants, depriving them of sunlight.

Also, both crops can be affected by similar pests, like cucumber beetles, which can spread bacterial wilt. Having these two plants in close proximity might increase the risk of pest infestations.

Finally, cucumbers prefer a bit more moisture than eggplants. Overwatering eggplants to satisfy cucumber’s water needs might lead to problems for eggplants such as root rot.

4. Broccoli

Broccoli and eggplants are both heavy feeders, which means they draw a lot of nutrients from the soil. If they are planted too closely together, they could potentially compete for these nutrients, which could stifle their growth.

Also, as a plant in the Brassicas family, broccoli prefers slightly alkaline soil with a pH between 7 and 7.5.

On the other hand, eggplants, which belong to the nightshade family alongside tomatoes, potatoes, and peppers, prefer slightly acidic soils with a pH between 5.5-7. 

In fact, the same incompatibility in pH applies to other plants in the Brassicas family, such as kale, cauliflower, brussels sprouts.  

The brassicas and nightshades are unlikely to flourish together because the soil conditions that help one thrive can hinder the other’s growth.

5. Cabbage

Cabbage is not an ideal companion plant for eggplants because of several factors.

First, cabbage is known to attract certain pests that can also affect eggplants, like aphids and flea beetles. If you plant them together, you could potentially increase the risk of these pests.

Second, cabbages are heavy feeders like eggplants, meaning they require a lot of nutrients from the soil. Planting them together could lead to competition for those nutrients, especially if not managed correctly.

Also, eggplants prefer warmer conditions, while cabbage is a cool-season crop. If you have limited space, you might not want to plant these together simply because they have different ideal growing conditions.

6. Asparagus

It is not ideal to grow asparagus and eggplants together since they have different growing requirements and growth habits.

Firstly, asparagus is a perennial plant that will continue to grow in the same spot for many years, while eggplants are annuals that are planted anew each season. This means that if you were to plant them together, the asparagus could interfere with the eggplant planting and harvesting process.

Also, asparagus prefers a slightly more alkaline soil (pH between 6.0 and 8.0), while eggplants prefer slightly acidic soil (pH between 5.5 and 7.0). These different pH preferences could make it more challenging to create optimal soil conditions for both plants in the same bed.

Moreover, asparagus has a deep and extensive root system that can spread up to several feet deep and wide, potentially competing with eggplants for nutrients and water.

7. Fennel

Fennels make a bad companion for eggplants, as the plants produce chemical compounds that can inhibit the germination and growth of eggplants.

Fennel is a flowering perennial herb closely related to carrots. All species of fennel are allelopathic, the seeds release chemicals that inhibit the germination of other plants nearby.

One study found that just 10% of fennel extract in water was able to completely stop the germination of seeds (Nourimand et al, 2011).

The allelopathy is not limited to the seeds alone, the roots of mature plants also release the chemicals. This makes fennel a bad good companion for eggplants or any plant for that matter.

Even without its allelopathy, fennel is still a bad companion for eggplants, because it has a large, branched, white taproot that can extend up to 16 inches into the soil. When paired with eggplants that have similarly deep and widespread roots, the two plants will end up competing for nutrients and moisture from the same zone. This will lead to both plants suffering from insufficient water and nutrients.

8. Corn

Corn is not a good companion for eggplants as it will compete for nutrients and also prevent sunlight from reaching the eggplants.

Corn is a heavy feeder that requires and consumes a lot of nitrogen to grow well.  Eggplants require equally large amounts of nutrients to produce their fruits. As such, having both plants together creates competition, and will deprive both plants of enough nutrients for optimal growth.

Another reason not to plant corn next to eggplants is that corn is tall and has multiple broad leaves that can create a canopy that prevents sunlight from reaching the shorter eggplants. Eggplants are sun-loving plants and require a minimum of 6 hours of sunlight.  The shade or partial shade created by the corn reduces photosynthesis and will result in reduced fruit yield.

9. Squash

Squash are also heavy feeders and can compete with eggplants for nutrients.

Apart from that, squash plants, especially vining varieties, can grow quite large and may overshadow smaller eggplants. Squash’s large leaves can shade out the eggplant, preventing it from getting the sunlight it needs.

Finally, squash usually requires more water than eggplants. Overwatering to meet the needs of the squash may result in waterlogged soil which is not ideal for eggplants and can lead to root rot.

Conclusion

In companion planting, the key is to pair plants that benefit each other in some way through pest control, improving soil health, or by being compatible in terms of growth habits and cultural requirements.

However, just because two plants aren’t “ideal” companions doesn’t necessarily mean they can’t be grown together; it simply requires more careful management of their individual needs.

For instance, ensuring that the plants are spaced sufficiently apart, rotating crops every year to prevent the buildup of diseases, and applying adequate amounts of water and fertilizer can help ensure that all plants get the resources they need.

Happy gardening!

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