If your plant is forming a lot of suckers, remove them and discontinue fertilizing. Quinces are susceptible to many of the same pest and diseases as Apples and other fruit trees. Some problems may be Fireblight, Oriental Fruit Moth, and Borers. Heavy pruning isn't required, except to remove dead, sick, or damaged branches. Some people cut out the inside branches to provide an open tree, which makes harvesting fruit easier.
Quinces begin to bear a year or two after planting.
The fruit ripens from about early September until well into October, depending on the variety. They are harvested when the skin turns from green to rich yellow. If you aren't using them immediately, store them in the fruit bin of your refrigerator, where they will keep well for about a week. Quinces can be increased by budding on the Angus Quince rootstock, or on Quince seedlings. Some varieties may be raised by hardwood cuttings.