Measure the water and coarse salt, using 30 g of salt per litre of water.
Place the water and salt in a saucepan. Bring to a boil over a low heat, stirring until the salt has completely dissolved.
If using a packet of pickling herbs and spices, add them according to the packet instructions. For the mix used in this recipe, the recommended amount was 2 tablespoons per litre of water.
Turn off the heat and leave the brine to cool until warm rather than hot.
Wash the jars and lids thoroughly with dish soap and clean water. Rinse well and allow them to dry.
Wash the green tomatoes and dry them with a clean kitchen towel. Discard any tomatoes with black spots, bruises, soft patches or insect damage.
Peel the carrots, parsley roots and horseradish. Cut the carrots into slices and the parsley roots and horseradish into sticks or smaller pieces. Peel the garlic cloves.
Place a layer of dried dill, carrot slices, garlic and horseradish at the bottom of each jar. Add mustard seeds and any additional pickling spices, if using.
Pack the green tomatoes tightly into the jars without crushing them. Fill the gaps with smaller tomatoes, carrot slices and pieces of parsley root.
Add more horseradish to the top of each jar.
Pour the warm brine over the tomatoes until they are completely submerged.
Place the jars in a tray to catch any overflowing liquid. Cover the openings with small, clean plates and leave overnight at room temperature.
The following day, check the brine level and top up if necessary, ensuring all the tomatoes remain submerged.
Close the jars and continue fermentation and storage according to a reliable, tested pickling method appropriate for your conditions.
Allow around one month for the tomatoes to develop their characteristic sour flavour. Check for signs of spoilage before serving.