I've read of many people wondering if it was possible to direct sow in self watering containers. The answer, for me, is YES.
I can see though, how there could be some problems if the soil mix was not just right. If the top layer of potting mix dries out too much it might be hard to keep the seeds at the proper moisture level. To ensure higher humidity in the top layer of soil I used scrap polycarbonate sheets cut to fit the containers. This creates a sort of mini cold frame using the container itself. The top of the soil has stayed completely moist, without being saturated. Early season this might not be required at all, but mid season and in summer it might be the only way to get the seeds to germinate. Wind and heat will evaporate surprising amounts of water from a self watering container.
If you are having a hard time getting the top inch of soil to stay damp, you may need to add a bit more sphagnum moss to the mix. It will pull more water via capillary action to the top of the soil. Too much peat will cause the soil to compact more, and have less aeration.
The photos below are of a self watering container with carrots direct sowed.
