Growing Cacti in Terracotta
I've had a long-standing preference for terracotta pots ever since I started growing cacti in 1971. Over the years
I got used to seeing those pots turn nasty, although I didn't think about how the nastiness was manifesting
their drawbacks. All that changed as a part of the ongoing education I've been enjoying through the CactiGuide
forum. Before we continue, I'll state that people have their own preferences for the pot materials they use,
so growers keeping their cacti in glazed ceramic or plastic pots won't encounter the problems I'm about to
discuss. I therefore offer the following observations for those of you who have been or will be using terracotta.
Exhibit A -- the effects of a porous clay pot after 2 years of regular watering:
The white residue on the outside of the pot comes from watering in hard water over the 2011 growing season. I started acidifying my tap water with 5% vinegar in January 2012. If I didn't, the Calcium bicarbonate residue would've kept building up. As to all the black stuff inside and out -- mildew perhaps? (If so, then maybe mildew likes acidified water too.) The plant that pot came out of has been free of pests and disease, so no reason not to reuse it. The best way to get out all the nasty stuff is by soaking the pot in water and vinegar -- 1 or 2 hours should be enough. Then a thorough rinse followed by drying it out. Here's what we get:
Now the pot is ready for use again. Well, not quite...
Residues on the outside of a terracotta pot can't be good. Treating hard water with acidification or using
rainwater is advisable for the long-term health of our cacti, but it won't duck the basic problem of keeping
them in porous clay over time. The reason is that some of the water and nutrients which should be going to
the roots are instead drawn away to the pot itself through evaporation. Growers who either don't know or
don't care if their cacti are over-potted will eventually find out that relying on evaporation to dry out
the mix is a bad strategy. It's best that you don't over-pot to begin with. However, assuming that you've
sized your pots properly, evaporation problems are still liable to catch up with you and your cacti even
though it may take years. For those who share my desire to keep using terracotta, you can address the
issue head on by waterproofing your pots first. I began doing it myself at the beginning of May 2012,
and I've been using a water-based product that permeates the pores in the clay. (In my opinion it's
superior to brush-on plastics that line the pots, but lead to cracks in the liner that will let
evaporation seep through.) After examining untreated and treated terracotta pots side-by-side for almost
a year, I can tell you that waterproofing works. Of course it'll have a limited lifespan, so this
is something I'll need to keep an eye on. With that said, the waterproofing can always be reapplied.
I'll stay ahead of the curve as long as I'm mindful enough to look for residues whenever they show
up on the outsides of my pots again. (I'm estimating about 8-10 years based on my waterproofer's
specs.) Not exactly high maintenance, though, and worth the price of admission with an effective
product to make your terracotta pots work for you the way they should.
Plastic and glazed ceramic pots both have their pros and cons. So does terracotta, but I've found it to
be the most suitable for my needs. If you agree, then I hope you'll find this article to be helpful.
Author: Steve Johnson, Los Angeles, California
All pictures by the author exclusively for CactiGuide