Hello GardenPreserver,
To prevent your fruit pie from sinking in the center, you need to manage the moisture content of your garden fruit. Fresh garden fruit contains a lot of water, which evaporates during baking and leaves a void. Here are the steps to fix this:
1. Use a thickener: Toss your fruit with cornstarch, tapioca, or flour before putting it in the crust.
2. Pre-cook juicy fruit: Simmer very watery fruit on the stove to reduce excess liquid.
3. Cool properly: Let the pie cool completely at room temperature so the starches can set.
Following these guidelines will give you a firm, beautiful pie every time.