Trim the ends of the chard stems and slice into sticks the height of your jar minus 1/2-inch for head space. Slice larger stems in half, or in thirds, lengthwise, so that each is approximately the same size. Pack them into clean, hot jars.
In a small saucepan, combine the vinegars, water, sugar, salt and spices and bring to a boil, stirring to dissolve sugar and salt. Pour over the chard stems, leaving a half inch headspace.
Wipe rim, seal and refrigerate for up to a month.