October 29, 2026

Growing green onions in water, then moving them to a bed

Green onions regrow in a jar of water for a few cuttings, and then the new stalks come in thinner each time. The white base holds a root plate and a store of sugar, and water supplies almost none of the nitrogen the plant needs to rebuild that store. Use the jar to get roots going, then plant the bases in a bed, where the soil feeds them and they keep producing through the season.

The steps below take you from a grocery bunch to a garden bed. Onions are hardy, so the move can happen earlier in spring than most transplants.

1. Save the root ends

Cut the green tops for the kitchen and keep the white base with its roots attached. Leave a short stub of white above the roots. That stub holds the growing point and the food the plant draws on to push new leaves. Pick bases with firm, pale roots. Slimy or brown roots have already started to rot.

2. Stand them in shallow water

Set the bases root-down in a glass with water covering the roots and the bottom of the white. Keep the cut top above the waterline. Submerged leaf tissue gets no air, so it softens and rots, and the rot spreads down into the base. Put the glass on your brightest windowsill. New green growth appears within days because the plant spends its stored sugar first.

3. Change the water often

Roots need oxygen. Still water loses its dissolved oxygen as roots and bacteria use it up, and the bacteria feed on sugars that leak from the cut tissue. Pour the water out and refill the glass whenever it turns cloudy or smells sour. Rinse the roots while you're at it.

4. Harvest a few times, then watch for thinning

Cut the regrowth when it reaches a useful length and leave the base in the glass. Each round draws down the reserve in the white base, and plain water doesn't refill it. The stalks come back narrower and paler, and growth slows. That thinning is your signal to move them. A jar gives you no reading of how much reserve a base has left, so you only find out from a thin cutting.

5. Harden them off before planting

Leaves grown on a windowsill have a thin waxy coating and have never felt wind, full sun, or a cold night. Set the glass outdoors in a sheltered spot for a short time each day and lengthen the visits over several days. The leaf surface thickens and the cells adjust to cold, which lowers the chance of scorch or cold damage after transplanting.

6. Time the move with your own frost record

Onion leaves build up sugars as nights cool, and dissolved sugar lowers the temperature at which the cell sap freezes. A hardened green onion handles nights that would kill a tomato. A fresh transplant has fewer roots and less stored sugar, so give it a stretch of mild nights after the move.

Your yard's nights may run colder than the forecast. Our published last spring frost date is April 28. This year our station logged the season's final frost on April 30. Our station's overnight lows run 7°F below the forecast, which pushes our effective last frost to May 20. We still direct-seeded onions into our ground bed on April 10 and harvested 38 between July 28 and August 2. Hardy alliums tolerate an early start.

Every Siltwell garden gets frost alerts. At 5 p.m. your garden's local time, Siltwell pulls the predicted overnight lows covering the coming two days. If either low reaches your threshold, you get an alert. A yard that dips below the forecast needs a microclimate offset, which you set in Settings under Garden, then Edit garden. To estimate the offset, the microclimate checker sets readings from nearby home stations against the forecast. For how cold onions and other hardy crops can go, see frost-resistant plants against your real low.

7. Plant into moist soil and keep it even

Set each base so the white sits at about the depth it sat in the water. Space them a few fingers apart. Water them in so the soil settles around the roots and closes the air gaps that dry roots out. Onion roots stay shallow and sparse, so they draw from the top layer of soil, which dries first under sun and wind. Drought stress concentrates the sulfur compounds in the leaves, which makes them tougher and sharper.

Between mid-July and early September, moisture in our ground bed ranged from 32% to 62%. Our raised bed 1 held a narrower band of 39% to 54% over those weeks. A shallow-rooted crop feels the wider swing first.

With a soil probe in the bed and a station connected, Siltwell alerts you when that bed dries. A push notification fires after back-to-back readings fall below 25%. Suppose your bed reads 24% and then 23%. You get one alert that day naming the bed, and you do the watering. The setup is in connecting a soil sensor to each bed.

What can go wrong

• Rotting bases. Stale water or a submerged cut top lets bacteria into the tissue. Trim off soft parts, rinse, and lower the water level.
• Floppy, pale regrowth. Low light makes leaves stretch toward the window. Move the glass to your brightest spot.
• Wilted tips after planting. Water roots are brittle and suited to standing water, so the plant pauses while it grows soil roots. Keep the soil evenly moist until new growth starts.
• A hard freeze right after the move. New transplants have less stored sugar than settled ones. Cover them for the night, using what to cover plants with for frost.
• Flower stalks. Onions are biennial, and a winter's cold triggers flowering the next spring. The leaves toughen once a stalk forms, so cut it early or let it set seed.

Once the bases settle, cut from the bed the same way you cut from the glass, taking the outer leaves and leaving the base in place. The soil refills the reserve between cuttings, so a clump in the ground keeps producing until it flowers. Start a fresh glass from your next grocery bunch if you want a second clump.