Do Sunflowers Kill Other Plants? We Asked a Plant Expert

Sunflowers may seem unassuming, and if anything, they seem like a very vibrant and cheerful addition to your garden. But recently, there has been a widespread idea that these flowers are essentially garden vampires.

According to this theory, sunflowers are suspected of killing other plants or at least taking away nutrients from other plants.

Before you confront the culprit or rush to dig them all up, know that this is a myth. According to two experts we spoke to, sunflowers are just great at taking nutrients from their surroundings, but they are not the plant killers that they are currently being made out to be.

Here’s why they’ve earned this reputation and how you can create a healthy garden that accommodates these tall, lush plants as well as other members of your garden.

Do sunflowers kill other plants?

The short answer is no – sunflowers do not kill other plants near them and this is just a myth.

“Sunflowers only become a threat when they are planted with non-companion plants, such as rhubarb,” says Sarah Warner, greenhouse manager at the Case Western Reserve University Farm.

This is because when planted together, rhubarb is at a higher risk of attracting snout beetles, which can be harmful to both plants.

However, it’s not just limited to sunflower intercropping. When you plant any plants that don’t go well together, chaos can ensue.

Warner says that planting non-companion plants together can increase the likelihood of pests and diseases. It’s best to do your research when choosing plants and planning your garden layout—whether or not you’re growing sunflowers.

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Do sunflowers steal nutrients?

Another no. Sunflowers are great at taking up nutrients and growing quickly, which is one of the reasons they appeal to gardeners, says Andy Ferguson, co-owner of Ferguson’s Orchards.

“Sunflowers have extensive root systems that can absorb nutrients and water far beyond their above-ground range,” he said, adding that they are also disease resistant.

So sunflowers don’t necessarily “steal” from other plants, but their needs are much greater than the few inches around the stem can provide.

Fortunately, this doesn’t necessarily mean it will harm surrounding plants, but it’s still something to be aware of.

Intercropping with sunflowers

There are many plants that can successfully share a space with your bright yellow flowers. Some of the best companion plants for sunflowers include marigolds, chives, watercress, and zinnias. Many of these help repel certain pests or prevent disease.

If you’re looking for fruits and vegetables, try tomatoes, lima beans, beets, lettuce, or blueberries. Warner has also had success with a variety of flowers, blackberries, and raspberries in his garden.

Tips for Keeping Sunflowers and Other Plants Happy

If you’re looking to maintain and enhance the health of sunflowers and other plants in your garden, Ferguson and Warner offer some tips worth following:

• Nutritional supplements: While your soil has a limited supply of nutrients, you can test and add your own. Ferguson also notes that compost and wood chips are beneficial for improving soil.
• Restrict root growth: Ferguson says this can be done by limiting the amount of sunflower roots that grow by blocking the roots or potting them.
• Add companion plants: As Warner mentioned, interplanting can create a mutually beneficial relationship between sunflowers and other fruits, vegetables, or flowers you plant near them.
• Rotate the position of the flower: Like other crops on the farm, you should rotate sunflowers each year to keep the nutrient levels in your garden more even, says Ferguson.
• Choose a smart area to plant trees: Think about where you place your sunflowers. Ferguson suggests the back edge of the garden—it helps set the sunflowers apart from other plants, but also gives you a visually appealing, taller backdrop to frame the garden.