Parsley stored stem-down in a jar of water, loosely bagged over the leaves, holds up for one to two weeks in the fridge — about three times longer than the same bunch sealed dry in a produce bag, where it usually wilts within four or five days.
Why a bag alone lets it wilt in days
A parsley stem cut from the plant does not stop working. Its leaves keep exhaling water vapor through thousands of microscopic pores called stomata, the same pores that let the plant breathe while it was alive. That process doesn't know the stem has been severed from its roots.
Water loss without replacement is what wilting is. Cells lose internal pressure, called turgor, and the leaf goes from crisp to floppy to see-through in a matter of days. Sealed in a plastic bag, the humidity around the leaves rises a little and slows the loss slightly — but nothing is refilling the tank. The bag buys a day or two, not a week.
Why a jar of water buys it another week
Put the same stems in a few inches of water instead, and the plant's plumbing does the rest. A cut stem still has intact xylem — the tube network that carried water up from the roots — and it will keep drawing water upward by capillary action for as long as the base stays wet and unclogged.
That's the whole trick: replace what the leaves are losing, at close to the rate they're losing it. Trim a half-inch off the stems first, since a stem end sealed by dried sap won't draw water. Loosely cover the leaves with a produce bag to slow evaporation further, and change the water every two or three days — standing water left too long grows its own film of bacteria, which will rot the stem ends faster than the leaves would otherwise wilt.
Wilted versus rotten — what's actually worth tossing
Most parsley that looks done for isn't spoiled, it's just lost water. Limp, pale, slightly yellowing leaves are still food. Turgor pressure can partially return if you submerge the whole bunch in ice water for ten to fifteen minutes, which is the same mechanism as the jar, just faster and more forceful.
What you should actually throw out looks different: stems gone dark and slick to the touch, black or fuzzy spots on the leaves, or a sour smell instead of a green one. That's bacterial or fungal decay, not dehydration, and soaking won't reverse it.
Freezing parsley for later
Parsley freezes fine for cooking, badly for garnish. Ice crystals form inside the leaf cells as they freeze, rupture the cell walls, and the structure that gave the leaf its snap is gone the moment it thaws. The parsley will be limp and slightly darker — useful in a soup or a sauce, useless on a plate.
The common method is to chop it, pack it into an ice cube tray with a little olive oil or water, and freeze the cubes solid before bagging them. One caution worth naming here: parsley packed in oil and left to thaw at room temperature creates a low-acid, oxygen-free pocket, the exact conditions Clostridium botulinum needs to grow. Freezing itself stops that, since the bacteria can't multiply at freezer temperatures — so keep oil-packed parsley frozen until you use it, and don't let a thawed cube sit out.