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I am a keen grower of runner beans and have grown them every year for the last 10 years. At the end of each growing season I have always just cut them down, let the root ball rot and then started again from scratch the following year by growing again from seed.
Recently, I have been questioning whether I have been doing the right thing in this, and have been asking myself whether runner beans can actually survive the UK winter and re grow year after year?
Well, here is what I’ve found out on the subject.
Under very specific conditions, it is possible for runner bean plants to survive the UK winter and regrow the following year. In very mild winters, plants in a protected position may survive by being cut back above the root, left in the ground and mulched. In harsher winters they may survive if the root ball is dug up and stored to protect it from the cold before being replanted in the spring.
It is important to bear in mind that if you do decide to try and overwinter your runner beans, their survival is by no means guaranteed.
Runner Beans are Perennials
In their native South America, where the climate is much warmer than the UK, runner beans are grown as perennials and are known by the name “seven year beans”, alluding to the fact that they will grow back year after year. Runner beans are grown as annuals in the UK as they are not frost hardy so are unlikely to survive the winter without some specific, targeted help.
What is the Average UK Winter Temperature?
UK winters have average temperatures of around 2C – 7C, but it is not unusual for temperatures to fall below freezing and frosts are common. The coldest temperature ever recorded in the UK was -27.2C during the winter of 1982 in Braemar, East Scotland.
What is Usually Done with Runner Beans in the UK After the Growing Season Ends?
Over the growing season, nodules on the roots of runner beans become filled with nitrogen. At the end of the season, once the runner beans have finished, it is common practice in the UK to cut them down to root level and leave the root in place to slowly rot down over the winter months. This nitrogen stored in the root nodules is slowly released into to the soil and come next spring you have beneficial nitrogen rich soil for subsequent crops. This is what I have always done.
How can I Overwinter Runner Beans in the UK?
So let’s take a look at the two primary ways that you can try to overwinter your runner bean plants in the UK:
1. Cutting Back and Mulching
The first option is to cut back the plant as you would normally do, leaving a small stem above the root in the ground.
If you live in a warmer part of the UK, if the roots are in a sheltered position, and if the winter is mild, you may find that this alone will be adequate for the plant will re grow next year.
Likewise, if you had been growing your beans inside a polytunnel or greenhouse, this would afford the roots some extra protection over winter.
But if not, you will need to give the roots some additional protection from the winter frosts if they are to stand a chance of survival. Applying a deep mulch around the roots is a good way to do this.
Then it is a case of waiting until spring and checking for any signs of growth!
2. Digging up and Storing
The second option is to dig up the roots and store them over winter. If you have any large plant pots to put the roots in they would be ideal – then try covering them in leafmould and house them in a location where they will be protected from frost.
Once spring arrives and the frost risk has passed it will be time to replant. When the soil starts to warm up around the replanted roots, new growth should (hopefully) begin to sprout.
4 Risks Associated With Overwintering Runner Beans in the UK
Overwintering runner beans in the UK does not come without its risks. Here we will take a look at the top 4 risks to be aware of:
1. There is no Guarantee it Will Work
You may go to the trouble of trying to overwinter your beans only to achieve a low (or no) success rate. Nothing is guaranteed.
2. The Strength of Crop may Vary
There are no guarantees when it comes to the strength of crops from older, overwintered plants either. There have been reports of strong cropping overwintered plants as well and weak – it is a risk you have to take.
3. There is a Risk of Disease
The older a plant gets, the more likely that it will become diseased. Growing from seed every year does not carry such a risk.
4. There is a Frost Risk as Plants are Likely to Shoot Early
If you successfully overwinter by leaving the root in the ground and mulching, shoots will usually to begin to appear as soon as the soil is warm enough in spring. This will normally happen once the temperature of the soil reaches or exceeds 10c / 50f.
We would normally only plant out runner beans grown from seed once the risk of frost has passed in late May or early June. To ensure that the new growth on overwintered plants is not damaged or killed off, a cloche or similar would be needed to provide protection from frost.
If you have overwintered the plant by digging it up, it is best to plant out gain once the risk of frosts is over.
By following the methods that we have looked at, it is entirely possible to overwinter runner beans in the UK although success is not guaranteed.
Whether this is desirable is another question. After all, new runner bean plants grow very quickly from seed, normally germinating within a week of being sown, and the strength of cropping from new plants grown is much more of a known quantity.
Personally, I will still try overwintering my runner beans this year. I will try using both methods to find out for myself whether it is it is a viable option to grow runner beans as perennials in the UK!