THE PLUNGE BED
This consists of a bed of moisture-retaining material such as well-weathered ashes, grit, or peat, outside the greenhouse in a sheltered place. When it is necessary to stand pot plants outside during summer the pots are immersed up to their rims in the plunging bed, which is kept thoroughly moist. Plastic pots should be plunged so that their rims are just below the surface, but when it is known that certain plants are to spend a fair time in the plunge during some stage of their culture, it is wise to choose clay pots for them. The clay is porous and will allow moisture through. Plunged pots are kept damp and cool throughout the day, whereas if they were stood in the open, on the ground surface, they would soon become baked by the sun and the plants ruined. Plunged pots are also less liable to blow over.
Another use for the plunging bed is in the growing of bulbs, which often need plunging after potting to ensure development of a good root system. This is especially important when forcing.
Whatever material is used for the plunge bed it can be kept in position by a rectangle of four boards. Alternatively a pit can be made in the ground if the drainage is good. The moisture retaining material must be kept moist – not waterlogged. For this reason a frame often makes a convenient plunge bed or a cover for one.