Trim off and discard leaves. Wash stalks; cut into pieces about 3 cm (1 inch) in size. This is a rough guide; no need to be exact.
Put the rhubarb to be canned in a bag or container and put in the freezer. Let freeze for 6 to 8 hours, or, overnight.
Put the rhubarb in a microwave-safe jug or bowl, and zap in microwave just enough to mostly thaw it -- don't cook. About 3 to 4 minutes per batch. Lots of liquid should come out.
Put the rhubarb solids PLUS the liquid in a large-enough pot on the stove.
Heat slowly and gently to boiling.
When it is boiling, the rhubarb will have been heated enough for packing. Don't cook it past that. You want stewed rhubarb pieces, not syrup.
Pack the boiling hot rhubarb into ready jars, trying to ensure that each scoop has a roughly equivalent amount of solids and juice.
Leave 2 cm (½ inch) headspace.
Debubble, adjust headspace.
Wipe jar rims.
Put lids on.
Process in a water bath or steam canner.
Process either half-litre (US pint) or litre (US quart) jars for 15 minutes. Increase time as needed for your altitude.