I have no idea what white half runner beans are, but I do frequently grown runner beans which look roughly like this and grow to around 9-12 inches in length (20-30cm for those who are metric).
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The flowers can be all sorts of colours. They are pretty easy to grow but like most beans and peas need plenty of water and water rich soil. They also like a good layer of compost to get their roots into and if you can line the trench they are to grow in with a layer of grass clippings and/or even old newspaper (I'm not kidding, it acts to hold water in creating a wetter environment) they will benefit from it even more. Runner beans in the UK grow very tall as well and like a lot of support. Typically they will grow to 6 foot high (2m) or more if allowed to.
