Repotting Oncidium sphacelatum

Our Oncidium sphacelatum was getting a bit too big for its old 20cm pot, so I decided to try my hand at re-potting. I've done a few Phalaenopsis before, but they have nice, big, chunky manageable roots. Oncidiums have rather thinner roots!

Oncidium sphacelatum

Too big! Note new shoot and roots.

Testing to see if 25cm is just about big enough!

I got hold of a 25cm pot, put about 2-3cm of fairly coarse gravel at the bottom (drainage and weight) and a thin layer of bark-based orchid medium.We found a 30cm pot last weekend, but I deemed it far too large to pot on an orchid, which in the experience of most growers prefer to be a bit "pot bound".

Gravel

Then it was time to see what the roots looked like after sliding it out of the pot.

Wow, that's some serious root system!

I was initially thinking of just "potting on" - i.e. putting the existing root ball into a bigger pot and cramming some medium down the sides. However, when I lifted the root ball upright, stones and old potting medium started falling out the bottom, so I decided to do it properly, and remove as much of the old medium as I could along with any obviously dead or dying roots. Interestingly, the crazy root growth was mainly just around the outside of the pot, with the central part of the pot more or less empty of roots. I rinsed the roots with my normal RO orchid-watering water - you should have seen the colour of the water in the sink after that (black!) - guess the medium was starting to degrade somewhat. 

Old medium plucked out, still masses of roots!

In its new pot.
Note old medium and roots underneath

Top down view. 

Turned out quite well, I think, and it seems very stable too. Hopefully, this plant will enjoy it's new home. There were quite a few new, active looking roots coming out of the pseudobulbs and new shoots, so hopefully, it won't sulk too much. There seem to be quite a lot of new pseudobulbs and shoots, so hopefully sometime next year we should see a nice display of flowers! Unfortunately, that light green ceramic pot no longer fits this one inside, so it's back to plain boring fake terracotta!

This plant was previously featured in these two posts: Pests: Black Fly, where it lost all its sprays of flowers to black fly and New Plant: Oncidium, where you can see it in pre-black fly blooming glory!