Hi again
@PicoAzores
Thank you for the thoughts about visiting the Azores and Portugal! I wish I could. A friend has spent many vacations in the Algarve and told many stories of its beauty. And great food.
You are very dedicated to having a garden! I've walked on hard lava flows in Oregon in the western USA. I can't imagine having to truck in soil and then garden on top of it! Do you think palms will be in danger of blowing over if they can only root 30 cm or so deep?
@CasaCostero and
@CalPolygardener have grown palms and so I think their comments are germane. I especially like Casa's suggestion to start small and watch the response. Also that it is better to add small doses more frequently in your conditions. I do this here for potted plants using soluble fertilizer at 1/4-1/2 strength with every watering. But I can get slow-release fertilizers that work well in soil in our climate. You will create a similar result if you apply small amounts more frequently.
Share some pictures sometime! Your garden and palms, views.
Pat
