I’m setting up a grow in a small greenhouse using a coco pearlite mix in smartpots. It will be mostly hand watering with what I think is called a water-to-waste system. I am wondering if watering spikes (the kind with an unglazed ceramic cone) that you screw a plastic bottle on as a reservoir, will work properly in this growing medium if I need to leave them unattended for a while. Any comments and advice are welcome.
Interesting thought!
Here is my theoretical thoughts on it 
If you pop the watering spike I would think it may drain out a lot faster than in soil. This would make sense due to oxygen, or air in general. Coco holds a lot more “air” than soil does, this may defeat the design of the water spike.
In soil the spikes work because once the soil is fully saturated there is no air left to enter the water spike allowing the water to release. As the soil dries naturally the air content increases, allowing air to displace water in the spike which lets it flow into the soil.
Where as with Coco and the higher air content the rate of water flow will be increased. Comes down to hydraulic pressure vs pneumatic pressure.
If you do try it or already did, I am curious as to how it worked out for you!