Tuesday, March 26, 2013

Why do my scarlet runner beans have no beans?



Last summer I grew an amazing bean hedge. Just six bean plants manage to densely cover a 4 by 2 meter section of fence. I was very excited thinking I was going to be drowning in beans. So it was quite disappointing when they provided nothing more than a mere handful. And it was even more disappointing this summer, when it happened again. With such great growth, foliage and covered in flowers, the plant is clearly thriving, you would think it would be highly productive. My gardening friend Debbie wonders whether the seeds I sowed were of an ornamental variety. Checking my garden diary, sadly not. Both scarlet runner beans, and from different sources.

Scouring the Internet for an answer revealed that there are allot of people on forums asking the same question. The common answer seemed to be temperature, with many people claiming that high temperature will cause the flowers to drop off or fail to set. It does surprise me considering these beans originate from the hot tropical climate of Central South America, but maybe the mountain regions are a lot cooler. Regardless it seems that gardeners in Tasmania have no problems growing them in summer, but for most of us on mainland Australia, not so good. The recommendation is to grow scarlet runners in Autumn, which is great news because it means I will be able to extend our bean producing period.


Unfortunately it is time for the chickens to enter the garden and the first bed to go is the one with the scarlet runners. I would love to see how they do over Autumn but the rest of the bed is finished and really needs the chickens to do their magic. So down they came. Last summer thinking that cutting the plant from the fence would be too difficult, I just snipped the plants at the ground and let them die and rot away on the fence. Of course this is a great waste of rich organic material. So this year I cut it down, and to my surprise it only took 30 minutes. I simply trimmed them back on one side, then they practically fell off the other.

Of course beanless beans is not a complete loss. What these bean plants would have done for the soil should be amazing. Bean and other plants in the legume family have formed an amazing symbiotic relationship with bacteria called Rhizobia. The plant feeds these bacteria within nodules in its root systems, and in turn the bacteria produce nitrogen compounds for the plant. Isn't that a lovely relationship? But what is even better, is that when the plant dies the fixed nitrogen is released into the surrounding soil, available for other plants to use. This is why I try and mix pea, bean or broad bean in every bed.

14 comments:

  1. Hmm, my farmer's market veggie people told me it was temp related too, I had the exact same thing happen.

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    1. Sounds like it is quite a common error. I hope you didn't try too many years in a row before you found this out. Thanks for sharing, it is always nice to know I am not the only one.

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  2. Definitely sounds like heat. Even though you're in Vic, through the summer months there, which can be extremely hot, maybe you could try growing some of the beans recommended for hotter climates ie Rattlesnake, Blue lake, Purple King, Epicure and grow the Scarlet Runner in spring or autumn.

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    1. I did do a number of other beans, including Purple King, and all were very successful. I have heard of someone who plants both Scarlet Runner and Rattlesnake to hedge her bets. BTW we are in SA, a touch hotter and drier than Vic.

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  3. I have the opposite problem; it's too cold where I live. Seeing as scarlet runner beans are actually perennial, I'm leaving mine in to see if they do any better the second year. Hopefully at some point, conditions will be perfect and they'll take off.

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    1. I thought about that, but the bed could really do with the nitrogen fixing and green manure that they can provide. So I didn't but I was very interested to see how they would go. I would love it if you reported back.

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    2. This year there were about two beans on the plant by the end of the cold Spring we had, then nothing during the heat of Summer. Then, in the last month or so it has set many beans. It seems to like a very specific temperature range - too temperamental for me!

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    3. Thanks for reporting back. Sorry to hear the second year also wasn't a raving success, but it was worth the experiment. And thanks to you sharing I too now know not to both with them again.

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  4. Even here in southern Tasmania we did not have a good crop this year as it was consistently warmer than usual. Peter Cundall said to pour a container of ice water onto the soil at night to cool the night time soil temp.

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    1. The ice water sounds an interesting solution. It does puzzle me though how that would work. From what I read it is the pollen that is killed by the heat.

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  5. I had the same problem and posted about it and got some advice which suggested they need humidity so I made an effort to mist the vine now and then. Whilst I was doing this I noticed that the plant was definitely setting beans but they were being nibbled off. They seem to be a favourite of the rodents in this area. Any chance the same fate could be befalling yours?- if not a lack of humidity might be the issue.

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    1. The humidity does make a lot of sense. As I said in the post, they originate in Central South America, which I believe is tropical. In my reading however there seems to be quite a lot of controversy over whether it is heat or humidity related. Rodents could be a problem, didn't notice any nibbles though.

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  6. Glad to read you cut the vines off. Did they grow back from the tubers the following season?

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    1. Well well well, I didn't realise they would regrow from tubers. As runner beans have tubers it makes sense that they would. But no mine didn't grow back probably because the chickens do an amazing job at clearing the beds.

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