Combine the cauliflower, carrots, celery, bell pepper, serranos, and garlic in a large bowl, then distribute the mixture evenly among four 1-pint glass jars with tight-fitting lids.

Bundle the dill in cheesecloth and tie it securely with kitchen twine to create a sachet.

Bring the dill sachet, vinegar, water, sugar, and salt to a boil in a large saucepan over medium-high heat—the sugar and salt should be completely dissolved.

Remove the pan from the heat and let the mixture steep for 10 minutes to infuse the brine with the dill's flavor.

Discard the dill sachet and return the brine to a brief boil over medium-high heat.

Pour the hot brine evenly over the vegetables in the jars, ensuring they are completely submerged.

Let the jars cool to room temperature on the counter before covering and transferring to the refrigerator.

Refrigerate for at least 7 days before eating to allow the vegetables to fully pickle and the flavors to meld.