Are your terracotta pots frost proof?

The last two nights we have experienced frosts with lasts nights feeling twice as cold as the previous one.

Whilst the morning sky was beautiful after a perfect starry might, the grass was white this morning reflecting the sharp dip in the night time temperatures.

In most cases, gardeners will have started to ease back or even cease watering their plants in pots as the plants near their life's end or move closer to dormancy.

Now is the time to decide, should you leave out the pot and risk the pot cracking or should we bring them in and not enjoy some winter or early spring colour?

What makes a pot frost proof?

Well, a pot basically becomes frost proof by being water resistant. As we all know, water, when frozen becomes ice and will have expanded considerably as it does so.

If that water was able to penetrate the pore spaces of the terracotta then inevitably the ice, when it expands, will blow out these pore spaces and ruin the integrity of the fired clay.

Many of the old clay pots that were used before plastic hit the scene are deliberately porous. This allowed water to move freely backwards and forwards with ease.

If you water a plant from the top it passes into the soil or compost and when the pore spaces are full, the water under hydraulic pressure would fall with gravity to the bottom. If there was not a drainage hole in the base then the pot would fill up and literally drown the roots as as all of the oxygen is expelled.

A porous pot allows this hydraulic pressure to dissipate the excess water which was essential in the days of plant production before plastic.

Now, many of these pots are used decoratively but unfortunately, they may not survive a harsh frozen winter.

If you are thinking of buying new pots for your autumn display or for next spring then look for a guarantee that the fired clay is indeed water or weather resistant, otherwise you could be looking at replacing them next year.

Sealing old terracotta (or new terracotta come to that)

Provided that you only use a suitable plant friendly sealant you can seal the pot to avoid water penetration.

One good method is a 10:1 water and PVA glue solution. Mix it up in a bucket or container that is large enough so that you are able to submerge your pot in the solution.

Dip it in for 30 seconds and drain off the excess and then leave to stand overnight to dry off. You will now have a pot that is sealed from water penetration.

It is also possible to use an exterior varnish. Thin down the first coat so that it is able to penetrate the surface of the pot - you may find it will suck it in quite quickly. This initial coat acts as a key and is necessary. Applying varnish as a one coat solution will often fail as this layer can flake away and allow water to penetrate underneath.

Leave this 'key' coat to dry and then repeat the process with a coat of undiluted varnish.

Lift your pot off of the ground to allow air to circulate and disconnect any possible water penetration from the soil or hard standing.

Now you should be able to leave your pots out in the coldest of weathers  providing the plant(s) themselves can stand it - but that's another matter.