Are you wondering can onions and beans be planted together? Beans and onions should never be planted together according to conventional wisdom; this rule has long been accepted within gardening textbooks and taught at various horticultural schools around the globe, yet why can’t onions and beans co-exist in one space?
As I had learned first-hand, beans and onions make an ideal combination. So it came as quite a shock when I discovered there is an unexpected chemical reason why beans and onions should not be planted together in one garden space. Herein, I will outline this science as well as provide solutions that might work in yours!
Reasons Why Shouldn’t Beans And Onions Be Planted Together?
can onions and beans be planted together? No, there are three key reasons as to why planting beans with onions would not work:
- Beans store nitrogen, so onions bolt (FALSE).
- Onions produce chemicals that stunt beans’ growth (TRUE).
- Finally, both beans and onions compete for moisture (TRUE).
So let’s address those theories one at a time:
- The initial impression, that beans act as nitrogen fixers and therefore supply too much nitrogen to onions is mistaken. Beans do fix nitrogen; they just don’t share it around like other sources would; in reality onions benefit from such relationships!
- Onions indeed produce chemicals that inhibit bean growth; hence the advice is to grow these vegetables separately.
- The third part, that beans and onions compete for moisture, is true but misleading. While both plants require ample moisture at different points during growth, neither is entirely reliant upon it for early success. As long as soil conditions don’t dry completely out before planting time arrives, both will thrive just fine! So this only represents a half-truth.
Do onions produce allicin and why does it harm beans?
Alliums produce allicin, an antimicrobial gas produced by all members of the onion family which makes us cry when cutting onions, as well as being responsible for garlic’s ability to cause sore hands when used directly on cuts or wounds. Allicin’s presence causes tears while cutting onions or cutting garlic bulbs. Though allicin doesn’t harm beans directly!
How does Allicin work to Inhibit Bean Growth?
Beans are nitrogen fixers. Regular allotment gardeners might know this phenomenon exists but may be confused as to its workings; nitrogen fixation in beans entails creating stores of nitrogen within roots, stems, and leaves to sustain sustained growth throughout their growing seasons.
Nitrogen fertilizers with high nitrogen concentrations tend to focus more heavily on root and leaf development, so leafy greens or climbing plants typically receive this kind of treatment more often than fruiting vegetables or flowering flowers.
By gobbling up nitrogen early in the season, they prevent other plants from using it when needed most. Something particularly significant when growing annual climbers like beans and peas which require substantial energy resources for their development.
Plants designed to fix nitrogen include:
- Peas,
- beans (including soy, cowpeas, and all legumes ),
- Lupins,
- Alfalfa,
- Peanuts,
- Clovers,
- Rooibos.
All utilize an enzyme known as Urease to process and store nitrogen for storage purposes; allicin is antibacterial while Urease remains bacteria-associated. If you follow science closely enough you’ll understand that allicin is the correct choice here!
Onions can restrict young beans and seedlings by emitting allicin, an antibacterial gas that kills beneficial urease bacteria required by beans and peas for fixing nitrogen, effectively impeding early development and creating weaker crops with shorter harvest cycles.
What nutrients do beans take up from their soil environment?
There’s a popular misconception that onions will gain too much top growth near beans because these organisms serve as nitrogen fixers; this misconception should not be taken literally and further investigation must take place on what exactly nitrogen fixation means in practice.
Nitrogen-fixing can be seen as part of rotation planting; specific “nitrogen fixers” should be planted before “nitrogen-hungry” crops to add nitrogen back into the soil after its removal from their root systems at season’s end. But these plants won’t leave behind much nitrogen for subsequent seasons until you dig through and turn up their roots at year’s end!
Beans store nitrogen throughout their stem and leaves, but their roots contain the highest concentration. No-dig gardeners can release nitrogen by cutting off bean tops in winter for composting purposes and placing them directly onto the ground with compost in spring; their roots also serve as slow-release nitrogen fertilizers that release slowly over time.
What will the consequences be of planting beans and onions together?
By and large, planting these two crops together won’t result in noticeable differences for either crop; however if your onions come under attack by maggots or suffer white rot, higher allicin levels could produce results that hinder early bean development.
As we do often with shallots and beans in panting shallots with beans, we found last year that our runner beans had significantly shorter stems compared to previous years.
Previous years’ French bean planting with shallots did not show any significant differences between plants with shallots at their roots and those with marigolds at their bases both sets grew equally well regardless of pairings.
How to Plant Onions and Beans Together?
Can onions and beans be planted together? Only recently have I discovered any issues between beans and onions after years of growing French beans and shallots together without incident, yet how could one possibly plant both at the same time if their interactions could prove toxic?
To successfully combine beans and onions, just follow their respective best practices for their growing. Onions should always be planted early (the earlier you can start sowing seeds near where you live, the greater will be their crop yields) in fall; similarly beans need to be started early as well in early summer or fall planting (see our separate pages on how best to grow beans and onions together).
Beans should be planted over several planting cycles for extended harvest time; just don’t sow directly in the ground! Onions do inhibit germination but this shouldn’t pose too many problems if started indoors (we use toilet roll tubes as root runs) before transplanting out onto outdoor beds or containers.
In early spring (assuming your beans/peas have their climbing frame), dig a trench behind them and fill it with fresh kitchen waste, straw, and torn newspaper; plant young beans into this hole before filling up any spaces left with garden compost.
Beans will feed off of decomposing food and paper waste deposited directly beneath their roots in a trench, while also storing nitrogen to benefit from the high nutrients available there. Although the antibacterial action from onions might harm them initially, ultimately their growth is ensured with ample nutrition available at their roots.
Plant new beans every two weeks from spring until early autumn for harvests that should continue into summer and early fall.
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Conclusion
Can onions and beans be planted together? My advice to any garden with limited space would be to simply experiment. Beans and onions do co-exist quite successfully even though science might dictate otherwise thousands of allotment gardeners and avid vegetable growers cannot all be wrong, including myself who’ve successfully grown onions alongside beans here!
While growing onions and beans together can present certain difficulties, you can do it successfully if space allows. On no-dig plots especially, beans and onions can help each other out by sharing nutrients. Just ensure any beans germinated indoors before planting out together!