Rinse peppers; let dry completely. Snip off stems at bases. Cut lengthwise slit down each pepper.

Place three 1 L pickling jars on rack in boiling-water canner; bring to boil. Into each hot jar, pack peppers up to shoulders; add one-third each of the dill and coriander seeds, peppercorns and cloves.

In saucepan, bring vinegar, salt, garlic and 3 cups/750 mL water to boil; reduce heat and simmer for 3 minutes. Straining out garlic through sterilized sieve, pour vinegar mixture into each jar, leaving 1/2-inch/1 cm headspace; with sterilized spoon, press lightly on peppers to release any air inside.

Screw on lids, then invert jars and let stand for 2 minutes, shaking occasionally. Lay each jar on side, roll back and forth, then set upright and invert; repeat several times. Set right side up and remove lids; with sterilized spoon, press lightly on peppers to release any air still inside.

Top up with remaining vinegar mixture (or, if none is left, with 1:1 mixture of vinegar and boiled water), leaving 1/2-inch/1 cm headspace. Screw on lids until resistance is met; increase to fingertip tight.

Place jars in canner, cover with water and bring to boil; boil for 15 minutes. Remove jars and let cool, undisturbed, for 24 hours. Check that jars have lids that curve downward; refrigerate any that do not for up to 3 weeks.

Makes three 1 L jars of 20 to 24 peppers each.