is it frost proof?

A couple of pots containing camellias had split over the winter.  I found new pots for the plants, and brought the old ones in to the hall to dry, so that I can glue the halves together with impact adhesive.  This works pretty well, and I should get another couple of years out of them, even if I just use them for temporary summer colour rather than permanent shrubs.  The split pots, plus the arrival in the morning's post of the Whichford Pottery catalogue, set me thinking about the performance of terracotta in frost.

We sell pots at work, and one of the questions we get asked is 'are they frost proof?'.  They are imported from Italy for the most part, and carry stickers promising that they are 'frost resistant'.  I explain this to customers as meaning that they should survive an average winter outside without damage, but that after a few years they will probably start to flake or split, and in a very hard winter like the December just gone they may disintegrate.  They decay because water can penetrate the clay, and when it freezes and expands it forces the terracotta apart.  There are more resistant pots around, I tell them, but sadly they are much more expensive, around a couple of hundred quid for a large pot instead of forty.  With terracotta you get what you pay for.  Most customers are satisfied with this explanation, and generally buy the forty quid pot.

It isn't really fair to say that Whichford are expensive.  They offer a ten year frostproof guarantee, and in practice their pots last at least twice as long as that.  I bought my first from them more than twenty years ago, and the only Whichford piece I have ever owned and no longer possess did not succumb to frost at all, but got accidentally run over by a truck.  The cost per year of owning a Whichford hand made pot is probably no more than for a mass produced garden centre one the same size.  Also Whichford's pots are more beautiful than the mass produced ones.  If only the initial capital outlay were not so high!  They are offering 10% off pot orders over £90 and free delivery (which is a significant charge normally, pots being heavy and bulky) until the end of the month.  I ought to partake of this offer myself, if only I had £90 to spend on pots, which I haven't.

A separate cause of splitting is pots that are narrower at the top than they are further down.  If the compost in these freezes the pot is practically bound to split as there is no room for the contents to expand upwards.  I try to steer people away from them if they want to leave the pot outside and planted up all year.  I've gone right off them myself anyway for permanent plantings as they make repotting so difficult.