You are picking the squash when they are too mature. Squash matures rapidly, requiring only five to seven days from flowering to maturity in hot weather. The key to high quality (tender and relatively seed free) is timely harvest; pick every other day in hot weather. Good yellow summer squash should be 1 to 2 inches in diameter at the base and pale yellow in color. Dark yellow or yellow-orange squash with a firm rind is over mature. Remove it from the plant and discard. If over mature fruits are not removed, the plant will stop producing fruit. For more help with this and other garden crops, visit the eXtension web site: Vegetables.