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The extraordinary scarlet runner bean

“She planted, as soon as the first strip was ready, runner beans and a row of lettuce. ‘The runner bean,’ said her book, ‘is not over-particular,’ and Caroline gratefully acknowledged the truth of the statement.”

— Margery Sharp, “Four Gardens,” 1935

At this point in “Four Gardens,” the year is 1916 and Caroline Chase Smith is married with two young children. Desperate for a diversion from housekeeping and the war, Caroline decides to rehabilitate the small, flowerless garden in the back of her house. Growing vegetables for her family is secondary to Caroline; what she wants most is the quiet and the solitude, and the muscle-pulling labor of digging in the earth.

When I read the part about runner beans and their “not over-particular” disposition, I thought back on my experience growing Phaseolus coccineus, commonly known as scarlet runner beans, for their beautiful red flowers that attract hummingbirds and bees. I grow a heirloom variety called Scarlet Emperor on teepees in The Bard’s Garden at Hanley Farm. (Why? A mischievous fairy in Shakespeare’s “A Midsummer Night’s Dream” brags that he can beguile “a fat and bean-fed horse.”)

Given agreeable growing conditions, my scarlet runner vines have produced an abundance of flowers and pods during July, August and September. Naturally more cold-tolerant, runner beans can be planted out in the garden before common beans (P. vulgaris); however, unless protected, our recent freezing temperatures — and snow! — could have been disastrous for seedlings.

It’s best to direct sow scarlet runner seeds after the last frost date (April 28-May 15 for our area, depending on your micro-climate). I scarify my seeds and soak them for 24 hours before planting. They need full sun and plenty of moisture early on, but are fairly drought-resistant later in the summer. I mulch around the vines to help retain moisture.

The tricky part of growing scarlet runners for me is that, similar to tomatoes, they don’t like extreme heat and will not consistently set flowers or develop fruits (bean pods) if temperatures hit the mid-90s and beyond. Early heat spikes have delayed flowering and pod development in my garden. Using cover cloth helps, but my scarlet runner crop is better when summers aren’t too awfully hot (or when wildfire smoke filters the late-afternoon sun — sorry for mentioning).

Scarlet runner beans are allogamous, which means they are prone to cross-fertilizing with other bean species. In fact, Charles Darwin used scarlet runners to demonstrate that some plants, like P. coccineus, are able to self-fertilize but are more likely to produce fruit if they are pollinated by birds and insects. Open-pollinated plants such as scarlet runners encourage genetic diversity within a species, which protects the species from being wiped out if/when local conditions change (from global warming, for example).

Here is other interesting information I’ve learned about scarlet runner beans:

Gardener and writer Monty Don has called runner beans, “quintessentially British” because they’ve been widely grown in England since the 1600s. However, P. coccineus originated in Central America and was domesticated in Mexico and Guatemala around 2,000 B.C.E. Don was referring to the fact that, historically, runner beans have been grown more frequently as a food crop in England than in North America, the latter where scarlet runners have been grown most often as an ornamental plant.

Another name for runner beans is the Oregon lima bean, because they grow better than lima beans in cooler climates (which is why runner beans were a staple crop in England).

As summers turn hotter in Oregon, I think it will become more difficult to grow runner beans (and perhaps less difficult to grow lima beans) without providing runners some protection from afternoon heat. (The OSU Extension Service discusses how “Climate change results in projected shifts in plant hardiness zones” at https://today.oregonstate.edu/news/climate-change-results-projected-shifts-plant-hardiness-zones.)

The Aztecs consumed runner beans as a remedy for intestinal parasites. These effects were most likely due to the fact that, like all beans, P. coccineus contains a toxic protein called phytohemagglutinin (PHA), and will cause stomach upset if eaten raw. The toxin is deactivated when beans are soaked for five hours and/or they are cooked in boiling water for 10 minutes.

All parts of scarlet runner bean plants — leaves, flowers, fruits, even the roots — are edible. The bean pods are best eaten when young — 2 or 3 inches long; otherwise, the pods become woody-tasting from thickened skins. The beans can also be eaten fresh after removal from the pods, or they can be stored and eaten as dried beans.

Scarlet runner beans differ from other Phaseolus species in several ways. First, they are tender perennials, rather than annuals, although they are usually grown as annuals in our area. Scarlet runners form tuberous roots that can be dug up and stored overwinter, then replanted in freshly composted beds the following spring. The advantage of doing this is they will grow more quickly as tubers than as seeds.

From start to finish, P. coccineus is a fascinating plant to grow. Mature seeds are speckled pink and black. Unlike other beans, they undergo hypogeal germination, which means the cotyledons remain beneath the soil’s surface. The vines climb in a clockwise spiral, unlike other beans that climb in a counterclockwise direction.

Handedness in twining plants is a genetic tendency called chirality. For gardeners, it’s useful to know a twining plant’s handedness when training the vines on a trellis or other support.

If you’re growing scarlet runners for their flowers, remove the developing pods to encourage more blooming. To harvest seeds, keep the pods on the plant until the seeds inside rattle when shaken.

One September afternoon, Caroline’s husband found her in the garden. Henry had something exciting to tell Caroline, but she was deeply engrossed in her scarlet runner beans “as though there was something extraordinary about them.” Of course, Caroline was right.

Rhonda Nowak is a Rogue Valley gardener, teacher and writer. She is founder and gardener of the Bard’s Garden at Hanley Farm in Central Point. Learn more at www.literarygardener.com, and email Rhonda at Rnowak39@gmail.com.