You can control weeds without herbicides by using companion planting. A study from Fields Crop Research found that certain legume plants create a “living mulch” that fills the space and blocks sunlight, making it difficult for weeds to grow.
These legumes also produce natural chemicals called allelopathic compounds, which interact with weeds and prevent them from sprouting.1
In addition, the publication “Better Together: The New Science of Companion Planting” includes plants that pair well with these legumes for better weed suppression.2
1. Crimson Clover + Cole Crops (Broccoli, Cauliflower, Brussels Sprouts & Kale)
Crimson clover (Trifolium incarnatum) is a type of legume that grows quickly and has bright red flowers. It helps improve soil health by adding nitrogen back into the ground, benefitting the plants that grow next to it. (ref)
It can also create a dense cover that prevents weeds from growing.
Cole crops like broccoli, cauliflower, Brussels sprouts, and kale thrive in cooler weather and are rich in nutrients. They need plenty of sunlight and space to grow but can benefit from the protection and nutrients provided by companion plants like crimson clover.
How They Work Together
- Weed Suppression: When you plant crimson clover alongside your cole crops, the clover grows quickly and forms a thick mat. This mat helps block sunlight from reaching weed seeds, making it harder for them to sprout.
- Soil Improvement: Crimson clover adds nitrogen to the soil, which helps cole crops grow better. Stronger plants can outcompete weeds even more effectively.
Growing Tips
- Planting Time: Sow crimson clover seeds in the fall or early spring. You can plant them a few weeks before your cole crops to give them a head start.
- Spacing: When planting cole crops, make sure to give them enough space (about 18-24 inches apart) so they can grow big and strong.
- Mowing: If the clover gets too tall, you can mow it down. This keeps it from overshadowing your cole crops and still allows it to work as a living mulch.
When it’s time to harvest your cole crops, you can cut down the clover. It can decompose and enrich the soil for future crops.
2. Medium Red Clover & Winter Squash
Medium red clover (Trifolium pratense) is a type of legume that grows well in many soils. It has small pink flowers and can reach about 1-3 feet tall. Similar to crimson clover, it adds nitrogen to the soil, which helps other plants grow.
It also creates a thick cover that can keep weeds from taking over.
Winter squash includes popular butternut, acorn, and pumpkin varieties that thrive in warm weather and need a lot of space to spread out. They grow on vines in the summer and produce large fruits that can be harvested in the fall.
Winter squash can benefit from the protection and nutrients provided by red clover.
How They Work Together
- Weed Control: When you plant medium red clover alongside winter squash, the clover grows thick and creates a ground cover. This cover blocks sunlight, making it difficult for weeds to sprout and grow.
- Soil Fertility: Medium red clover adds nitrogen to the soil, which is essential for healthy plant growth. This extra nitrogen helps the winter squash produce larger and more flavorful fruits.
Growing Tips
- Planting: Sow medium red clover seeds in early spring or late summer. You can plant them a couple of weeks before your winter squash to give the clover time to establish.
- Spacing: Plant winter squash 3-4 feet apart. This space allows the squash to spread out and grow while the clover fills in the gaps.
- Mowing: If the clover gets too tall, you can mow it back. This keeps the clover from shading the squash too much while still providing weed suppression.
If you’re harvesting your winter squash, you can let the clover stay. After the squash is done, you can cut down the clover and let it decompose in the soil to add nutrients for future crops.
3. White Clover & Strawberries or Blueberries
White clover (Trifolium repens) is a low-growing plant with small white flowers. It has a spreading habit, which means it fills in spaces well. Like crimson clover and medium red clover, it fixes nitrogen in the soil, which benefits other plants.
White clover also helps keep weeds down by creating a thick ground cover that blocks sunlight.
Strawberries are popular fruits that grow close to the ground. They like sunny spots and can spread out with runners. Strawberries need nutrients to produce sweet, juicy fruit, and they benefit from the nitrogen-rich soil that white clover provides.
Blueberries are delicious and nutritious fruits that thrive in well-draining, acidic soil and plenty of sunlight. Pairing them with white clover can help keep the area around them weed-free while adding organic matter to the soil as the clover decomposes.
How They Work Together
- Weed Suppression: When you plant white clover with strawberries or blueberries, the clover grows low and forms a dense mat. This mat blocks sunlight from reaching weed seeds, making it harder for them to grow.
- Soil Improvement: White clover adds nitrogen to the soil, which helps strawberries and blueberries grow stronger and produce more fruit. Healthy plants are better at competing with weeds.
Growing Tips
- Planting: Sow white clover seeds in the spring or fall. You can plant them alongside your strawberries or blueberries to give the clover a chance to establish.
- Spacing: When planting strawberries or blueberries, make sure to space them well (about 12-18 inches apart). This spacing allows both plants to thrive without crowding each other.
- Mowing: If the clover grows too tall, you can mow it down. This keeps it from overshadowing your fruit plants while still providing weed protection.
Come harvest time, you can leave the clover in place. After the harvest, the clover will help improve the soil for future crops.
4. White Clover & Tomatoes, Peppers & Eggplants
Planting white clover alongside tomatoes, peppers, and eggplants helps improve the soil and keeps weeds away, allowing these plants to thrive. They also benefit from the nutrients that white clover provides.
By planting them together, you ensure that your pepper plants have the support they need to grow strong and healthy.
How They Work Together
- Weed Suppression: When you plant white clover with tomatoes, peppers, or eggplants, the clover grows close to the ground and forms a thick mat. This mat blocks sunlight from reaching weed seeds, which helps prevent weeds from growing.
- Soil Fertility: White clover enriches the soil with nitrogen, which is essential for the growth of tomatoes, peppers, and eggplants. Stronger plants can outcompete weeds more effectively.
Growing Tips
- Planting: Sow white clover seeds in early spring or late summer. You can plant them a few weeks before or at the same time as your tomatoes, peppers, or eggplants to give the clover time to establish itself.
- Spacing: When planting tomatoes, peppers, or eggplants, space them about 18-24 inches apart. This gives each plant enough room to grow without competing with one another.
- Mowing: If the clover grows too tall, you can mow it down. This keeps the clover manageable and prevents it from shading your vegetables too much while still providing weed control.
After harvesting your tomatoes, peppers, or eggplants, you can leave the clover in place. It will continue to improve the soil for your next crops.
5. Cowpeas & Peppers
Cowpeas (Vigna unguiculata) grow quickly and form a dense canopy that shades the soil, preventing sunlight from reaching weed seeds. This suppresses weed germination and growth. Cowpeas, being legumes, also fix nitrogen into the soil. This benefits peppers by enriching the soil and providing essential nutrients for growth, without the need for synthetic fertilizers.
How They Work Together
- Cowpeas outcompete weeds for soil moisture and nutrients, making it difficult for weeds to establish.
- Peppers and cowpeas have different root depths and nutrient requirements, reducing direct competition between them while the cowpeas handle most of the weed pressure.
Growing Tips
- Planting Time: Sow cowpeas around the same time as peppers, but slightly farther apart to avoid too much competition for light early on.
- Spacing: Use wider spacing between pepper rows to allow cowpeas to grow as living mulch without overshadowing the peppers.
- Soil: Ensure the soil is well-drained and fertile. Keep the soil moist during critical periods of flowering and fruit setting for peppers.
Before cowpeas establish, hand weed around peppers to give both plants a head start against unwanted weeds.
Weed control doesn’t have to be a struggle. By using the right plant pairings, like those we’ve covered, you can naturally keep weeds under control while boosting your garden’s health.
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Davin is a jack-of-all-trades but has professional training and experience in various home and garden subjects. He leans on other experts when needed and edits and fact-checks all articles.