Glass Reinforced Plastic (GRP) planters are ideal for roof tops with limited weight capacity as, even though extremely durable, they are exceptionally light weight for their size.

Obviously it is not just the weight of the planters that needs to be taken into consideration when planning a scheme, but their contents too.

Above (fig 1) shows a simple cost effective way using polystyrene to reduce the weight in your planter, it also works as a great insulator against frost and heat too!

However, it is important to ensure that a small amount of drainage medium is placed at the bottom of the planter before placing any polystyrene, this stops the polystyrene from sealing any drainage holes in the base of the planter

How many litres will a planter hold?

Calculate the volume of your trough in cubic meters by multiplying the Length x the Width x the Height i.e. if your trough is 1500mm long by 500mm wide by 500mm High, the calculation would be 1.5 x 0.50 x 0.50 = 0.375 then multiply by 1000 and this will give you the amount of litres your trough will hold, in this example it would by 375 litres.

How much do GRP planters weigh?

All our GRP planters are made by hand therefore, sometimes the same size can vary slightly in weight, however, we do make planters with different materials depending on their size. As a general rule for planters in our standard range:

• Planters which are up to 0.7m³ weigh approximately 5kg per m²
• Planters that are 0.8-0.9 m³ weigh approximately 7kg per m²
• Planters 10m³ weigh approximately 8kg per m²

Although it will very much depend on the type and size of plants that you are planting, we recommend using the above chart [pie chart] as a reference for the percentage of planting materials. If trees or large shrubs are being planted then you may wish to consider using less polystyrene. Where the diagram states ‘other’ this refers to Root Refreshers, Mona tanks or an irrigation system. We also highly recommend drainage holes being put into planters that are being used outside.

What is the weight of compost

There are many different types of compost on the market, they are sold by the volume and not by weight, this is because the bulk density of compost depends on many factors, such as composition and how wet it is. As a broadly accurate guide, wet compost weighs approximately 1.5Kg per litre.

Europlanters specialise in large planters for roof terraces or roof garden projects. For support with your designs please contact a member of our design and build teams.