Plus, two combinations that are total myths.
You’ve heard of companion planting: The concept that by growing certain plants together, they can be mutually beneficial by attracting pollinators or repelling pests. That idea is based mostly on anecdotal evidence, folklore, and tradition, but occasionally, there are scientific findings to back it up. It's totally fine to experiment with companion planting to see what works for you.
But what about the idea of “nemesis” planting, or plants that don’t grow well together? Here, there's much more evidence to support why certain greens should not be planted in the same raised garden bed. First, some plants are allelopathic, meaning they release chemicals that inhibit the growth and fruiting of other plants. This idea has been studied in large-scale commercial growing enterprises for the purposes of issues such as weed suppression and crop productivity.
Another reason why plants may not grow well together is that they have dissimilar growth habits, such as a tall plant overshadowing a shorter plant. This means the more petite plant may not get enough sunlight during the growing season, so it won’t produce well. Or plants may have different environmental needs, for example, one plant may need more water than another. Other plants can also be aggressive growers, meaning they crowd out less vigorous plants.
While some plants are veritable "nemeses," for the aforementioned reasons, there are a few oft-repeated myths about certain plant combinations that have no basis in fact—and we're breaking two of those myths ahead. Read on to learn what not to plant together and what plant combo advice you can safely ignore.
One of the most commonly known allelopathic species is black walnut (Juglans nigra), which releases a compound called juglone in its leaves, stems, fruits, and roots. This plant causes stunted growth in many ornamentals, including rhododendrons and azaleas, and vegetables such as tomatoes, peppers, and potatoes. However, some plants, such as mock orange, forsythia, and garden plants such as squash, beans, and onions, are OK to plant near these trees.
Strawberries grown near members of the brassica family, such as cabbage, may be more likely to get infested by cabbage loopers, a type of caterpillar that will devour both plants. Keep these crops away from each other to avoid providing a smorgasbord for these pests.
Many types of tomatoes are indeterminate, meaning they’re long vines that keep growing (and producing) all summer. Because they need to be staked upright, you need to be mindful of what you plant next to them. Bush beans, for example, only grow up to one or two feet tall. Since both plants need a full six hours of sun per day, you should keep them separate in your garden.
Potatoes and tomatoes can be attacked by the same quick-spreading disease, late blight (Phytophthora infestans), which develops under cool, wet conditions. If your garden is hit, you could potentially lose both crops at once.
Lavender is a stunning perennial and a favorite flower of pollinators like bees. However, it doesn’t belong near most warm-weather veggies, such as tomatoes, peppers, and eggplants. That’s because lavender prefers poor, low-nutrient soils, such as sandy or gravelly types, while vegetables such as tomatoes need tons of water, especially when fruiting, and regular fertilizer to keep producing.
Read more: How to Grow Lavender Plants
Most types of mint are fast-growing, drought-tolerant perennials that thrive in a variety of soils. The problem is that mint is an aggressive plant, which will quickly take over garden beds. Plant mint in containers to contain its growth, rather than with other herbs or veggies.
Read more: 10 Pretty Perennial Herbs for Your Garden
Planting these veggies next to each other is mostly about space considerations: Most squashes, even those that grow in more compact bush form, reach three to four feet wide. Most vine types spread six feet or more. If you grow these plants, make sure your garden is large enough. These two also share the same pests, such as squash bugs, and diseases, such as powdery mildew, so you could lose your entire crop to the same issue.
Both of these savory herbs are worth planting in your garden, but they need very different conditions. While rosemary tends to prefer poor or sandy soils that stay on the dry side, basil likes more water. Plant them in separate containers, rather than the same garden bed, so you can give them the moisture levels they require.
Read More: How to Grow Rosemary
Sage and basil are two delicious culinary herbs that should be in every garden. But just like rosemary, sage tolerates dry conditions and poor soils, while basil does best in rich soils with regular moisture. Plant them in separate containers to keep these herbs happy. You could even plant sage right in your garden bed because it is perennial in much of the country.
Read more: We figured out the BEST Way to Keep Basil Thriving
Many gardeners have heard the myth that planting onions (or any other plant in the allium family, such as chives) near beans will stunt their growth. However, there has been zero science proving this. If you have a limited space and need to plant these two veggies next to each other, just do it!
Read more: How to Grow Chives in Your Own Backyard
Although you’ll see fennel noted as allelopathic, it’s a little more complicated than that. Research that's often cited was performed with fennel extract on seed germination in a petri dish, not in the garden with other plants! That means, despite the many times you’ll hear the warning that fennel doesn’t play well with other plants, no science has yet proven it. So, go ahead and plant fennel near other veggies in your garden if you enjoy its licorice-y flavor.
How to Get Your Garden Ready for Wintertime
The Ultimate Christmas Cactus Care Guide
This Is the BEST Way to Care for a Poinsettia
How to Protect Your Plants from Frost
