Re: crumbling terracotta

Reid Family wrote:
Hello All:
I am wondering if anyone can tell me why one of the terracotta pots on my deck is beginning to deteriorate on the outside near the bottom. I have two such large pots on the back deck from different origins. The crumbling one has a somewhat more porous surface, and about 2 or 3 inches around the bottom of the pot, the outer layer of clay is puffing up and then crumbling off. The pot is elevated on a sturdy little rolling palate my husband built for all my pots, so it always drains well. I have two suspicions: 1 is that the large amount of fertilizer that I give this greedy plant to keep it happy is somehow concentrating near the bottom and adversely affecting it. I'm not completely happy with this hypothesis, however, as the pot next to it, granted from a different pottery, which receives the same fertilizer regimen is fine, and because there is a layer of rock at the bottom that should keep the water from standing. I suppose it is possible that the salts are coming out of solution as they work their way to the bottom and clinging to the rock layer. My second thought is that the nasty little mites (or some other offensive pest) that have been a bane to this plant's existence, and a constant source of work to keep in check, are somehow laying eggs beneath the surface and heaving it up. I'm not convinced of this either, though, as I can't see why they would travel to the bottom of the pot! I only put this much work into these two plants as I love them so!

Karrie

Not all terracotta pots are equally well made, as someone else has suggested for instance Mexican pots tend to come in the less satisfactory category. I am pretty sure you are right though that the damage has been made worse (maybe even started) by excess fertilizer salts. Unglazed terracotta pots are notoriously bad at retaining water in hot weather due to evaporation of water travelling out to the surface through the material's numerous pores and if there is a lot of dissolved salt in that water it will pass out too..

One thing you may be able to do when you buy any new pot of this kind is to help protect it by painting the inside with a special goop to seal the surface. This decreases porosity and so reduces the need for watering in dry weather which can be a pain..

There is more than one kind of this sealing paint available here The one I have used is a local product called Terraseal. It looks like a grey kaolin and you paint it on thickly inside your new pot and then fill up with the mix just before the stuff is dry. With this surprising start it seems to work very well keeping water from seeping out the sides. I am sure there must be many similar products available in your much larger market.

Myself I use very few unglazed terracotta pots anyway, preferring either glazed ones or ones made of heavy plastic. Apart from using an internal sealing paint one can also line the terracotta with a slightly smaller plastic pot or even make a liner out of heavy plastic film with suitable holes pierced in the bottom.

As to the salts coming out of solution round the bottom of your pot. If one is using an artificial feeding regime this is not uncommon and it is usually recommended to give a big flushing with clear water from time to time to clear out the excess from both the mix and the pot fabric.

I would never myself use chemical fertilizers in any pot apart from slow-release types, which let no more of their content seep into the mix than the plant can use at any one time, so there is no excess to accumulate. For extra boosts I use only natural materials such as fish or seaweed extracts which do not create residues.

Moira

--
Tony & Moira Ryan,
Wainuiomata, North Island, NZ.     Pictures of our garden at:-
http://mywebpages.comcast.net/cherie1/Garden/TonyandMoira/index.htm
NEW PICTURES ADDED 4/Feb/2004

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