Green onion ends can make a glass of water look like a tiny vegetable garden. One gardener put cut grocery store onions on a windowsill and, eight days later, harvested new stalks that had reached more than 12 inches. The roots were in water, the tops were green, and the trick appeared to be working. Then a commenter pointed out what the glass wasn’t providing: nutrients.
Water can support another flush of growth, but plain water isn’t supplying what the plant would pull from soil. That matters if you keep cutting the tops and expecting them to return with the same flavor.
Her first harvest took eight days
The gardener started with green onion bases and placed them in water on a windowsill.
Eight days later, the new growth had reached more than 12 inches. She cut the stalks and put the harvest in the freezer.
A few stalks that appeared moldy went into the trash.
At that point, she planned to transfer the remaining onions into soil and keep them growing.
The new leaves aren’t proof that water is feeding the plant
Seeing fresh green leaves makes it easy to assume the roots are getting everything they need from the glass.
A commenter in the discussion pointed out the limitation: plain water contains no added nutrients for the regrowing onions.
The remaining onion base already contains stored resources. That can support new growth after the green tops have been cut.
It doesn’t turn a glass of tap water into soil.
Onion flavor needs more than water
The commenter singled out sulfur as important for the compounds associated with onion flavor.
Without access to nutrients, repeated regrowth can become less flavorful even while new green leaves continue appearing.
That creates an odd situation on the windowsill: the plant can look successful while the quality of what you’re harvesting starts changing.
The first harvest isn’t the same as an endless harvest.
Moving grocery store onions into the garden adds another question
After the first harvest, the gardener planned to move the onions from water into soil.
Commenters cautioned against putting grocery store alliums into a vegetable bed because their disease history isn’t known. One pointed to white rot, a disease affecting alliums, as a reason to avoid introducing unknown planting material into garden soil.
After reading the warning, the gardener changed her plan and decided to discard the grocery store plants and start from seed instead.
That concern is separate from whether green onion scraps can regrow in water. They clearly can, as her 12-inch harvest showed.
Use the windowsill trick for what it does well
Putting green onion ends in water can give kitchen scraps another round of usable growth.
Keep the roots in water and the green portion above it, and replace the water as needed. If stalks develop mold or decay, don’t add them to the harvest.
For continued growing, though, don’t confuse new leaves with a complete growing system.
Those green shoots on the windowsill are real. The first harvest can be real too. But the water isn’t providing the full nutrient supply behind them. The onion is doing more of the work than the glass makes it appear.
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