As designers we are sometimes presented with certain requirements from clients. One option that comes up on a regular basis is raised beds. It can be based on a trend or there is a perception that they are beneficial. It is important to differentiate between sectioning and ergonomics.
The general ask is raised beds made of railway sleepers. This poses two issues:
Firstly, reclaimed railway sleepers contain oils that can leach into the soil and are in fact not advisable for use to border any plants used for human consumption. If railway sleepers are to be used for this purpose then new should always be used.
The second issue of raised beds is to do with ergonomics, the outcome of a raised bed should be to make the use of the space more practical for people with mobility issues or who would have issues maintaining planting at a lower level. There is no difference in a border for plants or home grown vegetables at ground level or a 20-40cm raised bed. You still have to bend or kneel down to access it.
Both seem to be a by-product of misinformation on TV shows, poor design concepts that incorporate these and buzzwords.
If you use a raised bed idea to simply zone an area for purpose or provide an element of design then any option can suit, however if it is a question of ergonomics, we must use a different approach. If you do not want to bend down and put pressure on your back or kneel with bad joints, a raised bed needs to be at a height that reduces any of these factors or its function becomes redundant. A raised bed, to truly meet the purpose of the definition, needs to be much higher than most would suspect and must be based on what is most comfortable for use. However, using higher raised beds means you can incorporate seating into the design to make the space far more practical or add water or other higher-level design features.
Raised beds are very practical and building in raised areas of planting can really benefit a design for the purposes of aesthetics, however, you need to be clear on why the bed should be raised; if it is simply for interest and zoning the raised beds of sleepers or brick/rendered walls can add nice elements of design, but if the requirement is for practicality, our advice is to make them much higher or leave them well alone.