I figured out how to grow onions from an onion after tossing too many root ends in the trash. It started as pure stubbornness. I hated wasting food. Now I keep a steady supply of fresh greens on my windowsill and the occasional decent bulb in a pot. This method needs almost nothing extra. Just the bottom of a regular onion, some water, soil, and a bit of patience.
Honestly? The first few tries felt like a failure. The bottoms rotted. Shoots stayed skinny. I almost gave up. Then I tightened up the process and everything clicked. You can do the same. I’ll walk you through exactly what works for me, from the first cut to the first harvest.
Why Bother Growing Onions from an Onion
Grocery onions cost money. They sit in the fridge and slowly go soft. The bottom piece still holds life. I use that piece instead of buying sets or seeds every season. It feels practical. It also feels a little rebellious in a good way.
I grow mostly for the greens at first. They taste sharper than store scallions. Later I let some go longer for small bulbs. Results vary. Store-bought onions sometimes come with growth inhibitors. Organic ones or already-sprouting ones perform better in my experience. Still, even the ordinary yellow onion from the corner store has given me usable shoots.
See, the real win is speed. Green shoots show up in days. You start snipping for omelets and salads while the plant keeps going. Full-size storage bulbs take longer and need more space, but the greens alone make the effort worthwhile.
Getting the Onion Bottom Ready
Pick a firm onion. Soft or moldy ones fail fast. I look for one with a dry, intact root plate at the base. Organic works best when I can find it. Regular ones still succeed if they look healthy.
Grab a sharp knife. Cut about one to two inches up from the root end. Leave the root plate whole. Peel away the papery outer skin from that bottom piece. The rest of the onion goes straight into dinner. No waste.
Set the cut bottom on a plate, cut side up. Let it dry for 12 to 24 hours. This step matters. The cut surface needs to callous over. Skip it and rot shows up quick. I learned that the hard way after two mushy disasters.
Once the cut feels dry and slightly shriveled, you’re ready. The bottom should still feel firm overall. If it softens or smells off, toss it and start over.
How to Grow Onions from an Onion with the Water Method
This is the part most people start with. I still use it every time. Fill a small glass or jar with water. The water level should just touch the root end. Nothing more. Submerging the whole piece invites rot.
Poke three or four toothpicks into the sides of the onion bottom. Space them evenly so the piece balances on the rim of the glass. The roots hang down into the water. The cut surface stays above it. Place the glass on a sunny windowsill.
Change the water every one or two days. Cloudy water means trouble. Fresh water keeps things clean. In three to four days you should see white roots pushing out. Green shoots often follow close behind. When the roots reach about an inch long, move to soil. Leaving it in water too long weakens the plant.
I once left a bottom in water for a full week because I got busy. The roots grew long and thin. The base started to soften. Lesson learned. Transfer sooner rather than later.
Planting the Rooted Bottom in Soil
Choose a pot with drainage holes. Onions hate soggy roots. Fill it with a light, well-draining potting mix. I mix in a little compost or perlite when I have it. Ordinary seed-starting mix works fine too.
Make a shallow hole in the center. Set the rooted bottom in with roots pointing down. Cover with about one inch of soil. Leave any green shoots exposed. Water lightly until the soil feels evenly moist. Not soaked.
Put the pot where it gets strong light. Six or more hours of sun is ideal. A south-facing window works indoors. Outside, pick a sunny spot once temperatures stay above freezing. Space multiple plants four to six inches apart if you plant more than one.
If several shoots cluster together, wait a few weeks then dig them up carefully. Separate them so each piece has some roots. Replant the divisions. This step gives you bigger individual plants instead of a crowded clump of skinny ones. I skip the division when I only want greens.
Daily Care That Keeps Things Growing
Water when the top inch of soil feels dry. Onions have shallow roots. They like consistent moisture but drown in standing water. I check with my finger every couple of days. Overwatering is the fastest way to lose a plant. Underwatering just slows it down.
Feed every two weeks with a diluted liquid fertilizer high in nitrogen while the greens push hard. Once the base starts swelling into a bulb, ease off. Too much nitrogen late in the game can hurt bulb formation.
Pull any weeds by hand if the pot sits outside. Keep an eye out for soft spots or yellowing leaves. Yellow leaves often mean too much water or not enough light. Move the pot if needed. Trim any flower stalks that appear. They steal energy from the bulb.
I keep a small notebook for these plants. Dates of planting. First shoots. First harvest. It helps me notice patterns. Some bottoms give three solid weeks of greens. Others keep producing longer. Temperature and light make the biggest difference.
Harvesting Greens and Full Bulbs
Snip the green shoots whenever they reach six inches or so. Leave at least an inch or two of growth above the soil. The plant keeps sending up more. I use these like scallions in almost everything. Stir-fries. Salads. Baked potatoes. They taste brighter than the ones I used to buy.
For bulbs, wait until the tops start to yellow and fall over. That usually takes three to four months outdoors. Gently dig around the base to check size. Lift the whole plant. Brush off soil. Lay the bulbs in a dry, airy spot out of direct sun for a week or two to cure. Trim the roots and most of the tops. Store in a mesh bag in a cool, dry place.
Not every plant gives a big storage onion. Some stay small. That’s fine. I still get more food than I started with. The greens alone pay for the effort many times over.
Mistakes I Made and How I Fixed Them
I overwatered constantly at first. The bottoms turned to mush. Now I water less and check drainage every time. I also used old, soft onions. Firm ones work better. Always.
Crowding too many bottoms in one pot led to spindly growth. Giving each one space fixed that. Leaving plants in pure water too long made roots weak. Moving them to soil once roots appeared solved it.
Some store onions just refuse to grow well. I suspect residual treatments. When that happens I switch to organic or already-sprouting ones from the produce drawer. Success rates climb.
The biggest shift for me was accepting that greens come easier than perfect bulbs. Once I stopped chasing huge storage onions every single time, the process became fun again. Messy first attempts still beat buying everything at the store.
Frequently Asked Questions
Can I really grow a full onion bulb from a store-bought onion bottom?
Yes, but results vary. You often get smaller bulbs or mostly greens. Dividing the shoots and giving them good soil and sun improves the odds. Expect greens first and treat any decent bulb as a bonus.
How long does it take to grow onions from an onion?
Green shoots appear in a few days to two weeks. Full bulbs take roughly 90 to 120 days under good conditions. Indoors on a windowsill the timeline stretches a bit.
Do I need special soil or fertilizer?
No. Regular potting mix with decent drainage works. A light nitrogen feed every couple of weeks helps the greens. Stop feeding once bulbs start forming.
What if my onion bottom starts to rot?
Throw it out and start fresh. Rot usually comes from too much water or skipping the drying step. Keep only the root end in water and change it often.
Can I grow these outdoors year-round?
It depends on your climate. Start indoors anytime. Move outside after the last frost for best bulb growth. In mild areas you can plant fall crops for spring harvest.
I still get a quiet thrill when the first green tips push through. That little bottom I almost composted turns into something I can eat. It costs nothing. It takes almost no space. And it reminds me that a lot of the food we throw away still wants to grow.
Try one this week. Cut the bottom off the next onion you cook. Dry it. Root it. Plant it. Watch what happens. You might end up with a windowsill full of free greens before you know it. I did. And I haven’t stopped since.