The care you provide your planter depends on the material with zinc, wood and terracotta having special requirements. Composite modern material with fibre in their names require no special treatment, but be sure to be careful transporting them.


Zinc planters are produced in a two stage process involving hot dip galvanisation and the application of a coat. Hot dip galvanisation coats steel in a layer of zinc, which acts as a sacrificial layer, absorbing corrosive materials before they can reach the underlying metal. The planter is then coated, providing a finish.

While zinc provides unmatched corrosive resistance, it is still vulnerable to mechanical damage and impurities (trace elements) in the soil. The former exposes the underlying steel to the elements, causing a reaction to take place that produces ferrous hydroxide (rust). The latter can causes the zinc to react, stripping the steel of its sacrificial protection.

To maximise the life of your planter, we recommend you be careful when moving your planter. If you have trouble lifting, we have developed a pot mover for this purpose. To prevent zinc coming into contact with trace elements, it is important to use a liner, providing a barrier between the soil and the metal. Most of our planters come with liners, but you can always use non-biodegradable plastic.

Corten Steel

Cor-ten steel was specially developed for its corrosion resistance and tensile strength. Corten works differently than zinc in that it is not coated in a protective layer. Instead the steel has a special alloy added to it, which causes the surface to regenerate continuously when exposed to the weather. Therefore mechanical damage is not a problem.

Corten is not immune to corrosion. Pooling water will accelerate the corrosion process, so using a liner is recommended.


Wood can be divided into softwood and hardwood variants. Softwoods originate from gymnosperm trees and hardwoods from angiosperm trees. Angiosperm and gymnosperm plants are a major division in the plant kingdom, which produce woods with different cellulars structures. Angiosperms contain all flowering plants, indeed most species we recognise, while gymnosperms contain conifers.

As a rule of thumb, hardwoods are denser and more resistant to fire, but not all hardwoods are hard and softwoods soft. But these are not the properties we are interested in. As hardwoods and softwoods have different cellular structures they have different appearances, with hardwoods possessing prominent grains and softwood light grains.

Hardwood (left) with its distinctive grains.

The cellular structure affects resistance to decay and hardwoods can last up to 40 years untreated, softwoods significantly less. To combat this softwoods are treated with tanalith, producing a lifespan of around 20 years. This does not mean you can’t extend it further with varnish and using a liner to prevent contact with damp/organisms.


While terracotta is vulnerable to chipping and fracturing when dropped, its greatest drawback is its vulnerability to frost damage. As terracotta is a porous material, water can enter the material. Once water freezes it expands causing cracks in much the same way as potholes are formed on the road. You can combat frost damage by moving pots into an unheated greenhouse/garage come winter. Your plant will be fine, providing it is deciduous and has entered dormancy. Excessive warmth will cause your plant to come out of dormancy and must be avoided.

Composite Materials

Fibreglass, fibrecotta and fiberstone are composed of fibres combined with traditional materials such as clay and stone. They are superior to standard materials in every respect, being frost-hardy, non-reactive, durable, lightweight and cost effective.

Fibreglass planters can be maintained by wax polish, applied every 3 months, as can the other materials, depending if you wish to keep your planter in top nick, or allow weathering for a more natural look.

Jorge at PrimroseJorge works in the Primrose marketing team. He is an avid reader, although struggles to stick to one topic!

His ideal afternoon would involve a long walk, before settling down for scones.

Jorge is a journeyman gardener with experience in growing crops.

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