I added paper and shells into the concrete mixture. then oiled the pot once dry

Love the pots too .... I’m new to the forum... didn’t see a date of the post listed .... how is the holly doing ? How long has it been in the concrete pot ? I made some hypertufa pots and sprayed the inside with a rubber tree / pot sealant found in Walmart garden center ... haven’t planted anything in them yet .. your thoughts ?
Thanks !

I am curious as well! I was thinking about making some concrete bonsai pots and stumbled across this thread when I was googling around.

it has been over 4 years since the last update, and I have not seen the original poster on the forum since.

You can buy colour additives to put into your mix such as the one below.

www.amazon.co.uk/dp/B007YGWD7Q/ref=asc_d...gid=pla-429989234598

I made a pot last year and bought a concrete sealant for around £8 and the juniper nursery stock in it is growing very well so no side effects.

I have also looked at something called shape crete but it is not available in the uk. Paper crete is an alternative to make pots lighter.

Today I purchased some plasticizer. Watched a few youtube videos and the pots seem to come out much better with this added. Unfortunately I am not very good at making a mould so at the minute they are a little average. A slab is my next attempt.

G4 can be purchased in a variety of amounts. It’s what is used for sealing ponds and waterfalls. A small tin should be all you would need.

There seems to be a little confusion between acid and basic/alkaline here. Concrete is basic due to alkaline compounds in the cementing material. Alkaline materials dissolved in water result in a high pH measurement. Acid is low on the pH scale and it can dissolve the bonds in concrete. So, basically (pun intended) acid loving plants should not be planted in concrete because the leachate (Salts/lime) from the concrete can raise the pH of the soil to a point that they may not thrive. The high pH messes with the roots of the acid loving plants to the point that they don't successfully take in water and nutrients. Elms and Katsura, among others, prefer a pH above 7 (7 being the neutral point). They are good candidates for using an unprotected concrete pot. Acid < 7 < Basic.
Repeatedly soaking, drying, and rinsing can remove some of the excess lime. Sealing the pot with concrete a sealant should greatly reduce the pH changes.
I don't know if the Sealants have adverse effects on plants.