Drop in a Runner Bean seed before backfilling the hole with compost and watering the seed in. Runner Beans will germinate in about a week and grow surprisingly quickly. You will need to harden Runner Bean plants off for 7 to 10 days before transplanting them outdoors.irect sowing outdoors: Alternatively you can sow Runner Bean seed directly in the ground outdoors from May to July. Sow them at a depth of 5cm (2) and a distance of 30cm (12) apart in adjacent rows that are set about 45cm (18) apart.