Fine grit can be of marginal benefit for a heavy soil but what you really need is humus, Pt. Humus can come in many forms such as garden compost, well rotted manure with plenty of straw, composted bark, soil condotioner etc. The humus will add body to your heavy soil as well as nutriments, it will be beneficial to your plants and the worms and retain moisture in dry weather. You should probably aim at a covering of two or three inches and fork it in, repeating this annually if possible.

Agree with Bulbaholic completely - but if its really solid clay, the addition of horticultural grade grit would be useful. Sand is of little use.

Agree with both of the above. In addition, I usually mix some grit with the compost at the bottom of any new planting hole to give the roots help to get going.

Exactly as above - all sand will do in heavy clay soil is make concrete during the summer. Working in lots and lots of thick humus is the only way that I have found to improve heavy soil.

30 years ago, my parents moved to a place where the garden was seriously thick clay. I proceeded to add anything i could get my hands on to break the soil down....spent potting compost, rotten garden waste, sand, grit, leaf mould etc etc

I also dug the borders very rough for the winter and the weather broke the soil down.

To this day, the soil has been superb...still cly but very workable clay and let's face it, clay is probably the best soil of all....if you can manage it.

Good luck

thanks to all who responded to my heavy soil problem

As an afterthought, builders sand is a big no no, but coarse sand, sometimes sold as Calais sand is better. But as they others say, humus is the best thing. My mother once even buried an old mattress (not the sort with springs in) in our front garden, which was mostly builders rubble.