Old apple trees that have been neglected for 20 years bear little fruit, and what they do bear tastes poor due to the tree's neglect. Careful pruning of an old apple tree can help the tree produce more fruit, improve the fruit's taste and keep the tree healthy. The best time to prune an old apple tree is late in winter or early in spring, while the tree is dormant but after frost danger has passed for your area. Pruning over the course of two to three years will get the neglected apple tree looking much better.
Inspect the branches of your apple tree, looking for dead and diseased limbs. Dead limbs don't move in the air and feel hollow, while diseased limbs bear physical markings or discoloration.
Prepare a 1-to-10 solution of bleach-to-water in a bucket, and place your pruning tools in this solution. Cut limbs off at the base, or trim them back to a healthy Y intersection. In between each cut, dip your pruning equipment back in the bleach solution to sanitize it.
Discard all dead limbs and your bleach solution when you've finished removing unhealthy wood.
Remove one-third of the tree's growth to rejuvenate it. Prune away branches that cross other branches, branches that bend downward and branches that grow close to vertical. These cuts help open up the canopy and provide air circulation. Making them should take up your one-third quota, but if it doesn't, remove any branches that make a tighter than 45 degree angle with the tree trunk.
Continue to remove wood until you've reaches your pruning quota. Clear all discarded wood away from the base of the tree. If the wood is healthy, you can sell it.
Shape the tree the next year by removing another third of the tree's growth. Over two to three years your apple tree will grow new fruiting wood, and the careful pruning will help give the tree a strong structure once again.