Divide evenly onion, red pepper, garlic cloves, horseradish leaf, parsley, celery leaf, bay leaf, peppercorns and dill into bottom of each 1 quart jar.
Pack whole tomatoes tightly inside the jar.
Prepare the brine. Bring water, vinegar, salt and sugar to a rolling boil. Carefully pour over the tomatoes in the jar, leaving gap of ½" at the top. Place lid and screw into place, but don't over tighten.
Place tomato jars into a water canner, ensuring they are covered with water. Process for 15 minutes.
Remove from boiling water using a jar lifter. Using gloves, carefully flip over upside down on the counter and allow to cool overnight. After 24 hours, firmly press the centre of the lid. It should not move or bulge out indicating it is sealed. If it pops or clicks, it hasn't sealed, so keep in the fridge and enjoy within 2-3 months.