To be honest there is nothing particularly magical about runner beans but they do make a great subject for watching the rather magical process of a seed germinating. The main advantage of beans is that the seeds are large enough for you to see the root and shoot emerging with the aid of a clear plastic cup and two sheets of paper kitchen towel. Watch my two minute video on how to set it up.
Runner beans need water to germinate but do not need any other special conditions or treatment; they will germinate in the dark (underground) or in the light. The root always starts to grow first and it always grows downwards. The plant is sensitive to gravity and the root grows towards gravity, this is called Geotropism. The shoot always grows away from gravity (negative geotropism).
Whichever way up you plant the seed the root grows down into the soil and the shoot grows up to push out into the light. In runner beans the seed leaves remain underground and the first leaves you see are ‘true’ leaves. In many other plants the seed leaves appear above ground with the first shoot and you have to wait for the next leaves to identify the plant.
Unlike garden peas, runner beans are not hardy so they are often started off in pots in a frost-free greenhouse and transplanted into their final growing positions once the risk of frost has passed – in south east England usually early May. In a usual summer you do not need to supply additional water until the beans start to flower. Keep them alive if the weather is very dry or they are growing in a container but too much water early on just means that the plants will grow even taller and put energy into green growth instead of leaves. Once the plant moves into flowering mode, then water well. Feed container grown plants once beans start to form – tomato fertiliser is good as it is high in potash that encourages fruiting.