Companion plants are plants that have benefits for each other. They are better together than alone. As a gardener, you might have heard about the so-called nitrogen “fixing” plants. Now, that might sound very theoretical and only something for permaculturists. Growing legumes as nitrogen-fixing companion plants is actually very simple and also beneficial.
What are nitrogen-fixing plants?
Nitrogen is the first number in any NPK fertilizer. Nitrogen is essential in plant processes such as photosynthesis. It is also a catalyst for other minerals. In other words, having more nitrogen available in the soil is very essential for plant growth.
Nitrogen-fixing plants are plants that extract nitrogen from the air and convert or “fix” it into a form required for their growth. This happens through symbiotic rhizobia bacteria within nodules in their roots that take nitrogen from the atmosphere and make it available in the soil.
The best known and most common nitrogen-fixing plants are those in the legume family. Plants in the legume family are also desired on our plates and therefore in our garden.
Knowing the important benefits of legumes to other plants we can intentionally plant them in places where nitrogen is needed.
Growing Legumes as Companion Plants in the garden
Peas, chickpeas, fava, soy, dry and green beans, along with lentils are all legumes.
Most gardeners grow long rows of peas and green beans. For productivity that’s of course an option, but legumes can do so much more for the garden.
Grown together with other plants, they enhance the growth of the whole garden and greenhouse.
The only plants that do not like to be near legumes are plants from the onion family.
Pole beans and beets also do not like each other, grow bush beans instead.
In the garden, we often grow beans and peas along the edge of beds filled with other plants.
Or if a bed needs a bust, I might plant the whole bed with peas for one season.
Use common sense. If you grow heat-loving plants in a warm microclimate or under cover, beans that also like it warm, are good companions. If you grow cool-weather plants, peas would be a better choice as a companion.
Growing Legumes as Companion Plants in the greenhouse
In a greenhouse, legumes can be grown before the main crop, or together with the main crop.
Peppers and bush tomatoes might not leave enough room to grow legumes beside them, in this case, peas can be grown before peppers are planted. Read more about growing peas in an unheated greenhouse here.
Growing legumes under indeterminate tomatoes work really well. For that, I prefer dry beans. This way I do not have to worry about any harvesting till the very end of the season.
In the greenhouse, I plant beans after the tomatoes are well established. The main reason for the beans to grow there is the nitrogen-fixing ability. Any harvest is a bonus.
Getting all the nitrogen
Remember the roots of legumes have little nods on them, that’s where the magic happens. When the plant is done growing, cut the stem off leaving the roots in the ground.
This way you get all the benefits from the plant.
Early peas can be chop-and-drop as green manure under the plants. Or just compost the plant, leaving the roots in the ground.
Save seeds and replant
Saving seeds from legumes is so simple. The beans or peas that you harvest to eat are also seeds to grow new plants from. This way we get a natural fertilizer totally for free. It only takes a bit of extra planning.
Legumes are wind-pollinated, so as long as you do not grow different varieties directly next to each other, they should be true to type.
Here are a few more nitrogen-fixing companion plant varieties to consider that are not just beneficial, but unique and fun to grow:
We have grown Tom thumb peas twice in the same season because they grow so fast. Read more about it in planting a fall garden.
Scarlet runner beans, are not just nitrogen fixers, but also edible and beautiful.
Fresh chickpeas are a real treat and are not available in the store. The plants are also quite unique and fun to grow.
Why only grow green beans, purple is so much fun. Most of them do turn green when cooked, so no one will complain.
Tiger eye dry beans are very delicious. It’s a great dry bean for companion planting.
Edamame soybeans are a great choice for a hotbed or greenhouse. They can be used fresh as edamame, or dry.
What is your favorite nitrogen-fixing legume variety to grow?
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Oh no! I planted fava with my onions. It looks like they are both growing for now. Will the favas kill the onions or stunt them? If I should cut the fava for fertilizer when would I do that? The plants are around 15 inches tall and starting to set flowers. Should I wait till the pods form? Is chop and drop better than composting the tops? Should I leave the roots intact around the onions?