In the instructions for building raised beds you often read about lining the bed with foil. The purpose of this is to protect the wood from moisture and thus help the bed to live longer. However, not all slides are suitable for this.
Which film is suitable for lining a raised bed?
Rubber, PE and PU films such as pond liner are particularly suitable for lining a raised bed. They are robust, tear-resistant, waterproof and rot-resistant. Bubble wrap, specially made for raised beds, is also suitable and free from harmful plasticizers.
Damp wood rots quickly
The substrate in a raised bed should always be as moist as possible and not dry out. Wood, on the other hand, must never come into contact with moist earth, otherwise it will rot quickly. That's why you should always set up such a bed so that the lower edge can dry quickly after a downpour. Ideally, your raised bed has a plastic or metal profile to protect it from soil moisture so that the wood does not come into contact with the ground. If this is not the case, you can also place the bed box on a row of slabs or stones. However, you can protect the inner walls of the raised bed with a robust film.
Which films are suitable for lining a raised bed
Water-permeable fabrics such as fleece are not suitable as bed lining because there is a complete lack of protection against moisture. Rubber, PE and PU films, which are normally used for pond construction, are suitable for this. Pond liner in particular, which has to hold large quantities, is ideal for this purpose: it is very robust, tear-resistant, completely impermeable to water and resistant to rot. If you want to use sections left over from pond construction, the individual strips should overlap by a good ten centimeters at the seams. Bubble wrap made specifically for building a raised bed can also be used. This usually has the advantage that – in contrast to conventional pond liner – it is free of harmful plasticizers. The bubble wrap also serves as drainage, as excess water is drained away along the bed walls.
Raised beds that do not require any foil at all
The sole purpose of lining the raised bed with foil is to protect the wooden bed box from moisture damage. Of course, such a protective measure is not necessary for all raised beds: beds made of high-quality aluminum, Corten steel or stone, for example, usually do not require any additional lining, as these materials are more or less resistant to moisture. Plastic basically doesn't need a lining, but attaching a (safe) film makes sense for other reasons. Plastic often releases harmful substances into the substrate, so a film is inserted to protect against it.
Line the raised bed with foil - This is how it's done
Lining the raised bed with foil is very easy: it's best to simply fold the foil over the edge and secure it with a covering board. You can also staple them to the inner edge with a fabric tape and large, stainless staples or attach them with roofing felt nails. Attaching a fabric tape makes sense as it can prevent the film from tearing out. No further attachment of the film is necessary. So it can hang loosely in the bed, but should at least reach down to the ground.
Tip
The wood of the raised bed must under no circumstances be damp when attaching the film. After rainy weather, allow the wood to dry thoroughly for at least a day before sealing it with foil.
