I live in Phx Az USA, which is Zone 10a - desert clay soil. Everything
grows here! You can lighten the texture up with compost or mulch, and
change the acidity with some vinegar or coffee grounds, but most things
seem to grow well anyway. I just chop my stems and other mulchy trash
type stuff into the bed when I harvest and weed, which aerates and
composts it up a bit - but clay soil has great minerals etc. Just break
it up, don't let it get all compacted, and water slowly and deeply. I
use tons of mulch to keep the soil moist - you'll find that the clay
stays moist and you won't have to water as often as some other soils.
I used to think my clay-ey soil was a problem - now I know it's
actually a good place to start. I add a lot of compost so I don't have
to spend a lot on fertilizer, and grass clippings from my lawn and my
neighbors' lawns for mulch. As it breaks down, I just pile more on. It
takes FOREVER and a lot of organic matter added to the soil to get that
lovely fluffy texture of storebought soil, if that's important to you,
but you don't really need it to grow things. I aim for it just because
working in clay can be exasperating when you're trying to aerate and
till, and fluffy soil is so fun and easy to plant in.
One consideration is accumulation of salts. Since clay holds water - or
at least drains it away slowly, chemicals or minerals in the soil only
wash down as far as your watering depth. so if you water down a foot
over and over, you might find a layer of calcium, caled caliche, or
various salts, beginning a foot down. Out here, if you want to dig a
tree or help your drainage, you have to dig until you find that layer
of salt/caliche. If it's five feet down, you have to water until the
soil is wet six feet down, to start washing those salts away into the
earth. As for the caliche, once that calcium layer builds up, only a
pickaxe will break it up. It will occlude drainage until it's broken -
it forms a solid layer, just like calcium buildup on a water fixture,
or a bone spur for that matter.
May I ask where you live?