Welcome to the top of the crops! Today you will learn about growing runner beans in a polytunnel.
Runner beans are a great choice for home-growing, and can do well in a polytunnel. These legumes grow well and can produce truly prodigious yields.
We usually grow runner beans for their pods, which are eaten while they are flat and green, before seeds grow to maturity inside. But we can also grow runner beans to produce dried beans, to use as a pulse. These can also be highly attractive flowering plants – adding height and visual appeal to your vegetable garden as well as drawing in those all-important pollinators to your space.
The key things to remember if you want to grow runner beans at home is that these are sun-loving plants but they do best in a relatively cool and wet summer.
Phaseolus coccineus is a plant native to mountains of Central America, and it is perennial in its native range, though it is commonly grown as an annual in our climate. It is not a plant that will thrive in cold conditions and it cannot cope with frost.
Most runner bean varieties are vigorous climbing plants that will need a support structure up which to grow. However, there are now also some dwarf types, which are suitable for small spaces and even container cultivation.
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To grow well, runner beans need:
A sheltered position in full sun.
A tall and sturdy support structure (for most varieties).
Fertile, moist yet free-draining soil rich in organic matter.
They can be grown in the ground or you can also grow them in containers of sufficient size that are filled with a peat-free multi-purpose potting mix.
To grow runner beans you will usually need:
Runner bean seeds or young plants if you prefer not to grow from seed.
A suitable growing location.
A sturdy support structure of some kind.
Facility to water your crop consistently throughout the summer months.
Organic mulch materials.
Runner beans are not particularly challenging to grow yourself at home, and you can achieve remarkably high yields from a surprisingly small amount of space with vertical growing.
The area where you wish to grow your runner beans, whether that is inside your polytunnel or elsewhere in your garden, should be prepared well. This means ensuring that the soil is rich and healthy, adding plenty of organic matter where necessary to provide the right growing conditions. Ideally, the soil should be mildly acidic, with a pH of around 6.5.
Growing your own runner beans from seed at home is the most sustainable and eco-friendly choice that you can make. This is a good crop to make the most of whatever growing space you have available since the crop takes up little horizontal space but climbs high to give abundant yields.
If you would like to grow runner beans from seed then of course you will first need to choose a variety suited to your needs and wishes. (More on varieties below.)You will also need to decide whether to start seeds indoors, or direct sow runner bean seeds where the plants are to grow.
In most of the UK, especially colder regions, runner bean seeds are best sown indoors towards the end of spring. However, in warmer regions, you can also consider sowing directly where they are to grow, though even in the ideal areas, germination rates may sometimes be patchy.
Before you sow, in either case, it is best to make sure that you have prepared the site well, and that it is free from weeds and rich in organic matter. You should also make sure that you have your support structure in place.
Runner bean supports can take a number of different forms. Among the most common options are:
A-frame structures of bamboo canes or natural branches.
X-frame structures of bamboo canes or natural branches.
A wigwam of canes of branches, suitable for smaller spaces.
Even dwarf types usually need a little support, which can be provided in the form of branching twigs inserted around the plants to keep them off the ground.
If you have decided to sow indoors then you will need small pots, deep modules or soil blocks into which you can sow the seeds around 5cm deep. Water the seeds in well and place them on a warm, sunny windowsill, ideally in a propagator, to germinate.
Once the seeds germinate, grow them on in a warm and bright location where the temperatures remain above 12 degrees C. and water them regularly, never letting the soil/ potting mix dry out entirely. They can be hardened off and planted out once all risk of frost has passed.
In order for seeds to germinate outdoors the soil temperature must have reached 12 degrees C. This is usually from around Mid-May in southern areas and in early June further north. Make sure you do not sow or plant out too early.
You can use cloches to warm the soil if you wish, to prepare the area for sowing.
Sow the seeds around 5cm deep, two at the base of each of your canes or branches, which should be around 15cm apart. Once these germinate, remove the weaker seedling where there are two to leave just one plant per cane or branch.
If you are growing runner beans in a container, make sure the container is at least 35-45cm wide and deep for dwarf types, and at least 45cm deep and 75cm wide for climbing runner beans. Choose a heavy pot so that the plants don't topple over as they grow and fill it with a peat free multipurpose or loam-based potting mix.
You can usually expect to start harvesting runner beans from around the middle of summer, depending on when you sowed and the variety you have chosen. You should pick when the pods are still quite young and around 15-20cm long. Harvest regularly and you can continue to pick runner beans over the next 8 weeks or so.
Remember, however, that while we usually think about runner beans as the green vegetable, you can also grow on your runner beans to produce beans for shelling and drying, for use as a pulse. All runner beans can be used in this way as well. So consider leaving some to mature fully, then drying these beans to store over the winter months.
Runner beans – the green pods - will keep in your fridge for a week or so, and can be blanched and frozen for later use. If you have a pressure canner, you can also use these to safely put up your beans in jars.
The mature seed beans, removed from their dry pods, can be dried out fully for longer-term storage.
Runner beans are usually stringless when picked fairly young, and some varieties are stringless in any case. So traditional methods of preparation that describe getting rid of the strings is not always applicable today. Runner beans therefore can often simply cooked. They can be sliced up and boiled, steamed, or sautéed for use in a wide range of recipes.
Remember, the dried beans can also be used as a pulse, in the same way that you might use other types of beans. Just remember that fully dried beans will usually need to be soaked and cooked for a long time before they can be eaten.
You can purchase a wide range of runner bean seeds online. If you want plant starts, these are usually available from garden centres of plant nurseries in late spring and early summer – there will usually however only be a much more limited choice, so you will not have as many different varieties to choose from.
Caring for runner beans is very straightforward. The key things that you need to do are watering and mulching, and avoiding too much competition for your crop.
These are relatively thirsty plants and it is important to water your plants regularly, especially important when the plants are in flower and as pods begin to form. Be sure to set up a good irrigation system when growing in a polytunnel.
Remember that plants in pots or other containers will need to be watered more frequently than those growing in the ground. And always direct water to the base of the plants where it is needed, and try not to wet the foliage, flowers or pods.
In the summer, it is important to mulch well around your runner beans with organic matter. This mulch provides slow release fertility, protects and improves the soil structure, conserves soil moisture and helps to suppress weeds. Try a mulch of compost or well-rotted manure.
Weeding around your runner beans is important because the plants will crop best if they do not have to deal with too much competition for water and nutrients.
But remember that there are numerous companion planting combinations that you might consider.
Excellent varieties of runner bean to grow in the UK include:
‘Achievement’
‘Aintree’
‘Benchmaster’
‘Celebration’
‘Enorma’ - Elite
‘Firelight’
‘Firestorm’
‘Greshen’
‘Liberty’
‘Moonlight’
‘Red Rum’
‘St George’
‘Stardust’
‘White Lady’
All of these have an award of garden merit from the RHS.
Runner beans may sometimes fail to produce pods if the environmental conditions are not quite right. They may fail to produce pods if the soil is too dry, or if conditions are too acidic. They may also fail to produce well when it is particularly hot in milder parts of the UK over the summer or if a polytunnel or greenhouse overheats.
Aside from these things, runner beans are generally not troubled by many pests or diseases or other problems. Though you need to look out for slug or snail damage to young seedlings, and black aphids, these are rarely problems that get out of control in a healthy organic garden.
Make sure the tunnel is well ventilated so it does not overheat through summer.
Grow runner beans in the tallest part of the tunnel, with a suitable support, or choose dwarf types.
Install a good drip irrigation system to keep the soil consistently moist.
Companion plant to deal with aphid issues, and to bring the benefits of this nitrogen fixing plant to its neighbours.
Rotate these beans and other legumes through different growing areas for long-term fertility – making the most of their nitrogen fixation.
Frassinelli, A., (2023) The Best Way To Prepare And Cook Runner Beans. Daily Meal. [online] Available at: https://www.thedailymeal.com/1280542/best-way-prepare-cook-runner-beans/ [accessed 22/12/23]
