Outside in the shade and gradually moving them into the sun. In fact you could just have started them outdoors in the sun from the beginning.

Thanks floral_uk,

The reason I am trying to start them inside is I had numerous failures with seeding them outside.

If I cover the pots with anything, it just gets way too hot, and I believe I simply boiled a few batches like this, as nothing has sprouted.

If I don't cover them - the evaporation is so quick due to high temps that I am not able to maintain constant humidity levels - the soil is either drowning or dry

Have you tried sowing direct into the ground? I can't do that in my climate but I believe it is done in hot areas with success.

Thanks,

Unfortunately I can't, as the land here is sand and rocks, only cactus and agave can grow in it :)

I've put so many different seeds in the various containers outside (tomatoes, cucumbers, rucola, pepper, oregano, basil) you name it - and nothing starts, not a single seed, even with my careful tendering of the moisture. I am guessing it must be the heat. (even if I keep all those containers in the shadow, now that I think of it, they are all sitting on the tiles which get really hot)

I did have some basil success when I seeded them indoors.

Well all I can suggest is to try and find some other local gardeners and talk to them about what works for them in the Canaries.

Consider container growing. I live in a desert and container growing does extremely well.

"the evaporation is so quick due to high temps that I am not able to
maintain constant humidity levels - the soil is either drowning or dry"

There are many workarounds for that. One of the easiest is a water bath below your growing medium. I do that in the colder season by floating (watertight) seed trays on water in a fish tank. Invert a few glass tumblers as seed tray supports if floating doesn't float yer boat. If the sun's too strong, there's always a towel or pillow case to drape across the front of the glass.

I do that in our winter when we can have a 40F/22C temperature swing and the air is bone dry. You can get fogging on the inside of the glass with the top wide open.