Scarlet runner beans need full sun to bloom well and set pods. Give them the scarlet runner bean sun they crave, which means at least six hours of direct light each day. In return the vines hand you the heavy red flowers they are known for.
My back-fence vines sat in a spot that baked from morning until late afternoon. By July they were covered in red blooms, with hummingbirds working the flowers most mornings. A few extra seedlings went into a shadier corner near my privacy fence, where the sun barely reached past noon. Those plants climbed just fine and threw out plenty of leaves. But they handed me only a scattering of flowers all season, and almost no beans. The two patches went in on the same day, from the same seed packet, with the same soil and water. Light was the only thing that changed between them.
Full sun means six or more hours of direct light per day, not dappled or filtered light. That steady light is the fuel behind the heavy flowering. NC State Extension lists these as full sun beans, and the reason is simple. More light means more energy, and more energy means more blooms. Those blooms are what draw in hummingbirds and bees, so a sunny plant feeds your whole garden, not just you.
Deep shade flips the result. The vine still grows, sometimes faster than you expect, because it stretches toward whatever light it can find. You get long, leafy stems and a green wall on your fence. What you do not get is flowers, and no flowers means no pods. The next spring I moved my shady-corner survivors to a sunny raised bed. Same plants, same roots. They bloomed within a few weeks and finally set a real crop of beans. If your beans look lush but bare, lack of sun is the first thing to check.
Hot regions are the one place where a little shade helps. Scarlet runner pollen starts to fail once temperatures climb above 90°F (32°C), so the flowers drop without setting beans. During one brutal heat wave my full-sun vines stopped setting pods for two solid weeks, even though they kept flowering. A spot with light afternoon shade can shield the plants during the hottest part of the day and keep more blooms productive. Morning and midday sun, then a break from the afternoon glare, works well in southern gardens.
When you plan your bed, the runner bean light needs come down to one rule. Pick the sunniest spot you have. A fence or trellis that catches morning-to-midday sun is close to perfect, since the vines get the light they want and a sturdy structure to climb. South-facing and west-facing walls tend to soak up the most sun through the day. Watch your yard for a week before you plant and note where the light lands and how long it stays. A corner that looks bright at breakfast can fall into shade by early afternoon once the angle shifts.
Skip the deep shade under a tree or on the north side of the house, no matter how convenient that fence looks. You will get a handsome green vine and very few beans for your trouble. Put your plants where the light is strongest, and plant them along a fence or trellis that warms up early. A wall or fence also holds warmth into the evening, which the heat-loving vines enjoy. Do that, and the flowers and pods follow on their own.
Read the full article: Scarlet Runner Bean Growing Guide
