As I go around customers’ gardens helping to get them cleared up for the winter, I notice that many have emptied their pots and put them to one side waiting for spring to return. As a result, patios tend to look bleak and neglected during the dark winter days. It is not surprising that many people do this as terracotta pots are generally not frost resistant and there is a risk they will break during the winter period if left out. However, with the right type of pot it is possible to have a nice winter display.
So, what is the best type of pot to use? Before answering that it may be helpful to briefly cover the different pot types and discuss their suitability for external use during the winter.
Terracotta from the Latin terra cocta – meaning baked earth – is fired to about 1080 degrees Celsius and is porous in its finished state. Because it is porous water can soak into the pot and then when subjected to freezing conditions the clay will begin to flake and crack as ice forms. It is possible to treat terracotta pots with a sealant which will help to prolong the life of the pot by several years. However, in general, terracotta pots are the most vulnerable pot type during the winter.
The next level up is the Earthenware pot, which is fired to a higher temperature, typically between 1100 and 1200 degrees Celsius, and although normally glazed it may also be unglazed. Due to the temperature they are fired to these pots can be glazed in bright colours something which is not possible with Stoneware pots (see below for next pot type) which are fired at higher temperatures. When unglazed they are either a cream or buff colour.
These pots are often more durable than terracotta because they are less porous. However, water may still soak in via the unglazed interior area of the pot and thus cause the glazing to blow-out as ice forms. This risk can be reduced by ensuring the pot is well drained and not left standing directly on the patio. Raising the pot up off the ground with a small stand or pot feet (seen on the left) will facilitate drainage and help to reduce the risk of the pot cracking from frost.
Finally, stoneware and salt glazed pots which are fired to around 1280 degrees Celsius, are the most frost resistant. This is because the clay at this higher temperature becomes vitrified, a state where the clay is bound together so tightly that water molecules are too big to penetrate it. Keeping the water out means that the clay cannot be cracked from within as is the case with pots fired at lower temperatures. Typically these pots are quite dark in colour, see right.
Of course, there are other materials to consider for pots and planters which include: plastic, fibre glass, recycled rubber, wood, and various metal types too. The size and the material type of pot/planter you wish to use will clearly vary according to your budget and the style you wish to create. Pots/planters not made from clay may offer a greater of frost resistance but even metal can be affected by ice, just think of copper water pipes bursting in winter.
If you decide to stick with a clay pot then most frost resistant type is Stoneware. www.worldofpots.com have a lovely range of rustic stoneware pots they claim to be fully frost proof (see image and link to the right).
However, Crail has its own pottery (crailpottery.com) and I’m sure they would be pleased to advise as to the best pot to use.
In Part 2, suitable plants for winter display in pots