Plant Trials
Virtual runner bean trial
May 2006
Soil preparation
The runner bean plot was hand dug during winter and allowed to weather, creating a good frost tilth (i.e. soil broken down by frost action). The plot was then cultivated using a three-tined cultivator. Drawing the tines through the soil helps to break down large clods and loosen the surface. A wide plastic rake was then used to level the surface, remove any large stones and create a fine tilth ready for sowing.
Beans are generally hungry plants and demand a rich soil, the requirement for organic matter and additional fertiliser should be assessed by the gardener and added as required prior to planting. The soil in the trials field is already very rich and high in nitrogen, potassium and phosphorus, so fertiliser wasn't added to the plot; organic matter hasn't been added for a couple of years. Excess nitrogen can create a lot of unwanted soft growth, which would prolong the time taken for the crop to flower. Runner beans, as part of the legume family, have nitrogen-fixing root nodules. However, these constitute relatively little to the crop, so add 100g per sq m of a general purpose fertiliser at planting. If plants fail to thrive, adding 35g per sq m of high nitrogen fertiliser in June can be beneficial.
As the root area of legumes is fairly rich in nitrogen it can be dug in once cropping has ended, while spent foliage makes a valuable addition to the compost heap.
Support
In early May spacing between rows was measured out at 1m using an adjustable marking tool. This was then used to mark out each row at a width of 60cm and again to measure out each wigwam station at 60cm.
Four 2.5m high bamboo canes were inserted at the corner of the resulting 60cm x 60cm grid. The canes were pushed 45cm into the ground, slightly deeper than the usual 30cm to avoid wind rock and for ease of cultivation and picking. The canes were then tied in.
The wigwams have been staggered to allow a good deal of light through the crop to ensure strong, even growth. Fresh canes were used to avoid transferral of red spider mite. Vegetable Trials Committee member Sarah Wain of West Dean Gardens recommends having two sets of canes in order to use them every other year for this very reason. Alternatively, scrub canes with hot water and garden disinfectant before use.
Sowing
A 5cm deep drill was created on each corner of the wigwam using a hoe.
Three seeds were sown in each drill and will be thinned to two plants per cane, removing the weakest.
Soil was then raked to cover each drill before raking the entire area around the wigwam.
Due to water shortages in the south of England, the trial is to be watered using drip irrigation as required. Drip irrigation systems can use up to 75% less water than a standard sprinkler. Laying the hosing close to the plants allows the water to drip directly near the roots avoiding wasteful evaporation. Watering at the start or end of a day, rather than in the middle of the day will also avoid much of the water being wasted in evaporation. With this in mind the trial will be watered in the evening.
Initially irrigation hosing was laid around the outside of the first row. It was decided that as well as looking untidy, the hosing would not sit as tightly to the canes and plants as when watering from the inside and therefore it was moved inside the wigwams and the rest of the plot laid accordingly.
The bean seeds were watered in well when sown on Wednesday, 24 May. Watering prior to flowering should not be necessary, unless the plants show signs of wilting, as this will aid foliage growth at the expense of flowers. Substantial watering during the flowering period greatly increases the concentration of flowers and aids setting of pods.
As runner beans are high-altitude plants native to Central America, they require high moisture levels and cool night temperatures once flowering commences. While warm days are preferable, warm nights can lead to pods failing to set. On such an evening flowers can be damped down and cooled by spraying with water, which may assist setting in such circumstances.
The RHS runner bean trial was sown on Wednesday, 24 May. Sowing was planned for Monday, 22 May but heavy rain at Wisley prevented this.