I moved to a new residence last December, and spring has been revealing a few perennials and a new challenge: clay soil.
There are three beds that the previous owners obviously worked, and I've added composted manure to these. Some of the other areas are full of lumps of clay. The lawns (I hate lawns) are bumpy with lumps of clay rising.
Gypsum will help to break clay down so the clay can be mixed with organic matter.
I would spread a layer of gypsum over the clay and then layer on compost and/or well rotted manure. It may take a year or two to get the clay beds into good growing shape.
Dew worms will bring clay to surface in lawns. I used gypsum on the clay when I used to try to grow lawns. I am moving away from lawns and grass towards alpine , wildflower and sand bed garden areas.
Lots of clay down here - fellow I know brought in truck loads of gravel and dumped it in his gardens - gravel not sand. Said it breaks up the clay then slowly sinks and provides better drainage. He grows heather and has amazing gardens. I have not tried this but go for lots of organic material and in a lot of cases - raised beds.
Well Calgary is certainly full of clay at least in my area. New top soil lots of amendments sure help. I hear gypsum is good as Caroline suggests .When I had the back yard landscaped we stripped off about 12 inches of clay on one side of the yrd. But you know it is still there, the ground cracks when things dry out. But we still garden successfully!
As for gravel - I would say forget it! There was some gravel left on my garden area when the landscaping was done and then the new top soil on top. I swear the gravel still grows down there - that was in 1992 and every year there are still rocks coming up!
It does break the forces which hold clay particles together.
It takes over a year for it to break about 1 or 2 inches of clay.
I sprinkled the granular form of gypsum over the clay and let nature work.
The next spring I could get my pitch fork into the top layer of clay and mix it with
Andrew, where are you presently located? More in the east end? My garden is FULL of the Ottawa Valley Leda clay. ( http://www.museumstuff.com/learn/topics/Leda_clay ) If you can get it broken down, it's quite rich in nutrients, but as you know, it gets hard as a rock when it dries out. I think your best option is to bring in soil I've used the mix of garden loam and mushroom compost that Maurice Yelle sells. And the last time I called for soil, he delivered it in an hour. If you don't need to plant immediately, consider 100% mushroom compost and build up your gardens. If you dig out the clay you'll get a bathtub effect.
I coped with minimal effort by digging in a few bags of composted manure (from Loblaws, and it contained weed seeds -- not composted enough or hot enough). I'm not planning to stay here past next spring, so I decided not to invest time, energy, money etc. into the soil. Hating the lawn, but it's that kind of neighbourhood. Most of my plantings have been in containers where I can control the soil, but I did plant some pole beans, chard and tomatoes.
The biggest problem has actually been earwigs, which are even eating my brugmansias. Wretched, destructive, hideous creatures.
Thanks for your advice, everyone.
PS I went on a cruise in April and took a shore excursion in Roatan, Honduras, to the botanical gardens and a bird and butterfly sanctuary. Here's a photo of a flower I couldn't identify -- looked like a mallow-family but hairy. I'm in the process of putting all of my cruise pix on flickr, so if you're interested, let me know and I'll send you the link. --A