X3. Gypsum will help, but it won't be a cure all. Add as much organic material as you can get your hands on, then go scavenging for more. If you are itching to get some good gardening going, start with a lasagna garden, then work on expanding the rest of your garden area. You can also do green manure (or cover crops) to help break up that clay. Look for crops which have a deep root system, will winter kill and which will add a lot of green matter to the ground. Some cover crops which will give you extra benefit include regular peas, green beans, you might try planting a block of bird seed. Buckwheat is an old stand by. You can get 3 crops in during the typical summer, then follow it with a stand of winter rye which can be tilled in in the spring. Or you can use annual rye grass towards the end of the summer. It will winter kill, then you can just roll the carpet of dead grass back to prepare and plant your soil. I recommend a minimalist approach regarding tilling when it comes to clay. In the long run, tilling is counterproductive b/c it produces a heavy hard pan: The tines of the tiller slap those clay particles and work them into an impenetrable layer of hard clay that won't allow roots or water to penetrate. In a nut shell: keep that soil covered at all times year round with a growing crop, a cover crop, or a deep mulch (minimum of 6").