Take it out of that pot and put it into a nursery black pot. You want the soil to warm up.

Encephalartos tend to love heat. They will root and flush faster in warm climates. In your coastal climate, I say just be patient with it and don't water too much so as to avoid rotting it.

I wouldnt keep them or other types of heat lovers like Pachypodiums,Adenium and the like in ceramic pots. You will here in the bay area lag far behind what you would have gotten if you went to the black commercial nursery pot.

If you ever get one to the size thats just right- or in no hurry,then light colored pots,ceramic,terra cotta will suffice.

@stanofh The soil I am using is very hot soil. It has small rocks in it and gets quite hot on a sunny day. Gritty mix simulates a desert soil.

The plant is already in a plastic container, but I don't believe that a thin plastic is going to retain heat better than a ceramic in any case. I don't understand why you would focus on that issue.

@Josue I heard that in their natural South African environment it is both hot and humid, and during the summer it tends to rain a lot there. I thought these plants like a lot of water but must be in well draining soil to prevent rot?

Yeah,hot soil. Ok.

@Josue great information on climate in South Africa where Horridus grows.

The point on the container is really an argument for a dark color like black, rather than an argument for plastic versus ceramic?

Okay, I decided to take this plant out of the soil, and it actually had extended the deep root quite a lot. It's growing the root structure very well. The problem was the roots are long and vertical and stringy. I had pushed the caudex down into the soil and the roots directly under the caudex "buckled" and were loose. I tried to plant it deeper and get the roots aligned vertically, so not it has much more firm rooting near the caudex.

I think the argument is that a black plastic container will heat the soil, while a ceramic container (any color) will keep the roots relatively cool.

You'll have to be patient with encephalartos. Horridus and cerinus are both very slow growing plants. Plant them and forget about them. You're in for the long-haul with these cycads.