Wash the green beans thoroughly. Trim the ends off the beans.
Prepare your jars: Clean pint or quart jars and lids. Place one garlic half, mustard seeds, peppercorns, dill, and red pepper flakes (if using) into the bottom of each jar.
Pack the trimmed green beans tightly into the jars vertically.
In a saucepan, combine the vinegar, water, and pickling salt. Bring the mixture to a boil, stirring until the salt dissolves completely.
Carefully pour the hot brine over the beans in the jars, leaving about 1/2 inch of headspace at the top. Ensure the beans are fully submerged.
Tap the jars gently to release any trapped air bubbles. Wipe the rims clean.
Seal the jars with the lids and rings. Let the jars cool to room temperature on the counter.
Refrigerate the dilly beans for at least 24 hours before eating. They will continue to develop flavor. Store in the refrigerator and consume within 4 weeks for best crunch.
Notes
For a crispier bean, you can soak the trimmed beans in ice water for 30 minutes before packing them into the jars.
If you prefer a stronger dill flavor, substitute 1 teaspoon of dill seed for the fresh dill sprigs.
If you want to can these for shelf storage, you must use a water bath canner and follow tested canning procedures for safety. This recipe is for refrigerator pickles only.