Taken from the Eclectic Gardener @ http://www.teachinggarden.org/

Written by Alan Hickman

In the early years of colonization, the flat clay soils of the Peel Plain were so productive that the region was known as the bread-basket of Canada. Despite a hundred and fifty years of ploughing and half a century of reliance on manufactured fertilizers, the soil is still rich in micro-nutrients. There is neither too much of anything - like aluminum - to poison the soil nor too little of anything - like boron perhaps - to stunt plant growth. What does need attention with Brampton soil is its tendency to be wet and cold in spring and to dry-out and crack-open in summer.
Although there seems to be no precise definition for the word 'tilth', good tilth describes the mechanical condition of a soil which is easily workable and in which plants have a good chance of thriving. Soil which has good tilth is friable, without being dusty, and moisture-retentive, without being soggy. A farmer assessing a new piece of land will pick up a lump of soil and squeeze it through his fingers and can tell immediately if it has good tilth.
Tilth is a function of the particle sizes in the soil. A soil which contains roughly equal parts of clay, silt, fine sand and coarse sand is called a loam and it will usually have good tilth. To be defined as clay, a particle has to be less than 0.002 mm across. A grain if silt would be between 0.02 and 0.002 mm across. Fine sand is between 0.2 and 0.02 mm across and coarse sand is from 2.0 mm and 0.2 mm. For comparison, a human hair is about 0.075 mm in diameter so a grain of fine sand might be the same size.
As each larger particle type is one thousand times the volume the one before, the difference in size between a particle of clay and a particle of coarse sand is quite enormous. Using the same proportions, if a particle of clay was the size of a glass marble, a grain of coarse sand would be the size of a house.
Clay particles vary from barely visible to the naked eye to sub-microscopic. They are so small and light that they float in the air and can be carried thousands of miles on the wind. It is mostly airborne clay which sticks in a thin film to the screens of computers and TV's. In water, clay particles are the last things to settle out and it is suspended clay particles which give glacial lakes - like Lake Louise in the Rockies - their distinctive blue colour.
In a loam soil, it is the clay component which has the greatest effect on tilth. If the clay component is raised to 30 percent or more, the soil becomes a heavy clay loam - but, coarse sand has to rise to more than 70 percent of the mixture to create a light sandy loam.
Fortunately for Brampton gardeners, the cure for heavy soil which bakes brick hard in the summer lies close at hand. A truckload of coarse sand can come barreling down the Caledon Hill and be in Brampton in about twenty minutes. Sand is the real quick fix. It's cheap, and - unlike other quick fixes - the effect of sand in soil is permanent.
Sand can be applied at any time and it can be applied a little now and then for a cumulative effect. A half-inch of coarse sand can be raked into a lawn in spring and/or fall and an inch or so can be scratched into the soil around the plants in a perennial bed.
For anyone contemplating making a new flowerbed for next year, now is the time to get the job done. If the bed is to be on what is now lawn, the task couldn't be more simple. Just use a garden hose to mark the edge and remove a strip of sod about 8" wide all around the periphery of the new bed. Don't throw the strip of sod away, just flip it over and leave it where the bed is going to be. Cover the area of the bed with a three - or four-inch layer of coarse concrete sand. Cover the sand with three or four inches of your own garden compost - or composted leaves from the Region of Peel - and then go indoors and hibernate for the winter.
Come spring, where the plants are going to go, use a fork to roughly mix up the compost and sand and a bit of underlying soil - the grass will have pretty much rotted away by April. There is no need to bother digging up the spaces where there are no plants. That part will get mixed-up in the fulness of time.
If you're wondering what happened to the peat-moss and the bags of stuff that are supposed to break-up clay, well, the peat-moss stayed in New Brunswick - where it belongs - and the other stuff likely went somewhere to make drywall. Apart from the pollution caused by trucks hauling plastic bales hundreds of miles from the east coast, peat-moss is a non-renewable. When the long term solution is so close to hand, using peat-moss to temporally mask the effects of excess clay in garden soil is one of the more egregious misuses of our limited natural resources.