Wash the radishes well and pat dry, Trim off each end, set aside.
Place the radishes, quartered onion and jalapeños in the food processor and chop until fine (avoid going too far or they will turn to mush). Depending on the size of your food processor, you may have to do this in batches.
Add the chopped veggies to a large stockpot along with the mustard seed, canning salt, sugar and vinegar.
Bring the mixture to a low boil and cook for 10 minutes. Remove from the heat.
Pour into hot jars allowing 1/2 inch headspace. Wipe the rims and apply the lids and bands.
If canning, process in a hot water bath for 20 minutes.