Polythene sheeting for mulching
Sheets of thin black polythene make a good mulch: they retain heat and moisture and prevent weed growth, but do not add any food or humus to the, as do organic mulches, such as leafmould and straw.
When applying a polythene mulch before planting, prepare the soil in the normal way, then lay the black plastic sheeting over it, overlapping strips if more than one is used, and weighing down the edges with soil. Then make slits with a knife or a pair of scissors at the appropriate distances and insert the plants through these. Before mulching, water the soil thoroughly to make planting easier and ensure a ready supply of water for the plants.
If you want to mulch established plants, make larger slits and guide each plant carefully through each slit. For large plants, cut holes in the plastic and tuck it close around the stem. Inspect the soil regularly under polythene mulches; although plastic mulching considerably slows down the rate of evaporation, the soil will eventually need watering.
Black polythene is also very useful for forcing or blanching vegetables.
Plastics for greenhouses, frames and cloches
The use of plastics as a covering in place of glass for greenhouses, frames and cloches has increased rapidly in recent years. Both flexible and rigid plastics can be used.
If you are buying or making a greenhouse, frame or cloche using flexible polythene, it is especially important to make sure that the plastic is clear (not tinted with any colour) and of a horticultural grade, so that it does not deteriorate quickly in sunlight and— most vital— lets the maximum light in.
Flexible plastics that are a good deal stronger than polythene are available, such as PVC and PVA (acetate) sheeting. These are frequently sold under various trade names. They are longer-lasting than polythene, particularly if reinforced with nylon or wire.
If you want to make a more permanent, stronger structure, use one of the rigid plastics, such as rigid PVC. This is available in corrugated sheets, for extra strength.
Plastic has its uses in glass greenhouses, too. In metal-framed houses, the glass can be embedded in a strip of plastic sheeting to weatherproof the frame and prevent the glass from rattling in the wind. It is always handy to have a roll of polythene sheeting to make temporary repairs to any broken panes to keep the heat in.
Whether you have a glass or a plastic greenhouse, it is well worth the extra expense to insulate it, using polythene sheeting (of the horticultural grade, of course), during the cold winter months.
One promising new type of polythene sheeting is white on top and black underneath. This is particularly useful when employed as a mulch or as an under lay for peat-filled plastic growing bags, in the greenhouse or patio, particularly during dull winter months. The black undersurface acts exactly as a conventional black polythene mulch, retaining moisture and warmth and suppressing weed growth, while the white upper surface reflects light back onto the plants so that they receive as much as possible.
Trays or pots of plants can also be stood on these sheets, and the staging or lower walls of the greenhouse covered with metal foil or white emulsion paint to increase the light reflecting power.
Plastics are particularly useful for making plant propagators. You can buy a wide range of sizes to suit your needs, from the smallest, rigid-plastic covers for individual pots ofor to large, sophisticated propagators with thermostatically-controlled air and soil heating.