Regrowing vegetables from kitchen scraps: what really comes back

Some kitchen scraps really do grow again, especially spring onion bases and lemongrass stalks. Most, though, only give you leaves back, not a new root or a whole new plant, and plain water only gets you so far because plants need nutrients from soil. This lesson sorts what truly regrows from what gives leaves only, when to use water and when to move to soil, and a few things you shouldn’t plant from the shop.

What really regrows and what gives leaves only

Scrap	What comes back	How to start	What to expect
Spring onion base	new leaves	water, then soil	easiest; new leaves in about a week
Lemongrass with its base	a new plant that forms a clump	water until rooted, then soil	roots in 1-3 weeks if it is going to root
Lettuce base	new leaves from the centre	shallow water	slower than spring onion; a few cuts
Celery base	leaves	shallow water	leaves for flavouring; thick stalks don’t return
Carrot and beet tops	leaves	shallow water	leaves, no new root
Garlic clove	garlic greens	soil	greens come fast; a new bulb takes months
Shop potatoes	not recommended	use inspected seed potatoes	often sprout-inhibited and a disease risk

Water or soil

Plain water lets a base root and push up new leaves quickly, because the plant is living on what it has stored in the base. Once that store runs out, it has nothing else to draw on. A University of Utah writer, from their own trials, found that spring onions regrown in water several times lose flavour and nutritional value, so they use each base only once.

A simple rule: use water to get started, then move the plant to soil once the roots are about 5 cm (2 inches) long if you want to keep harvesting. In soil it gets nutrients, grows bigger leaves and gives more cuts.

Get these three things right with water:

1. Cover only the roots. Keep the top of the base above water; a fully submerged base rots.
2. Change the water every 1-3 days, or whenever it turns cloudy or slimy.
3. Give it light. A bright windowsill that doesn’t get scorching hot.

Water only gets a scrap started. Anything you want to keep picking needs to go into soil.

Worked example: one bunch of spring onions, day by day

Buy a bunch of 10 spring onions with the roots still on.

1. Day 0. Use the green tops for cooking and keep the white base with roots, about 5 cm long. Stand them in a narrow glass with about 1-2 cm of water, enough to cover just the roots.
2. Days 2-3. New leaves start pushing up from the centre. Change the water.
3. Day 7. The new leaves are long enough to cut. Cut 2-3 cm above the base: another meal’s worth of garnish.
4. Days 7-14. When the roots reach about 5 cm, move all 10 bases into a pot of potting mix, water well and put it in the sun.
5. After that. Cut leaves when long enough, always leaving the base. In soil you get several cuts; some sources say about 3-4 before the base is spent. When the leaves keep getting smaller, pull the bases out for the compost and start a new bunch.

If they stay in water the whole time, stop after one or two cuts.

Lemongrass: a real new clump

Lemongrass is a scrap that gives you a whole new plant, not just leaves. The condition is that the stalks you buy still have their base attached; stalks with the bottom trimmed off will not root.

1. Choose plump, firm stalks, and buy a few extra, because not every one will root.
2. Stand them in a glass with enough water to cover the base, somewhere warm and bright.
3. Change the water every 1-2 days to keep fungus away.
4. Roots should appear within 1-3 weeks. If a stalk hasn’t rooted by then, it usually won’t.
5. Plant in soil once the roots are about 2.5-5 cm long.

Pot size, sun and how to cut lemongrass so the clump keeps spreading are in growing Thai kitchen herbs in pots.

Celery, lettuce and carrot tops: leaves only

Washington State University Extension in Ferry County tried kitchen-scrap gardening and found that a celery base regrew leaves good for seasoning soup, but the stalks did not come back. Lettuce bases regrew more slowly than onions, and a baby beet with its top intact kept producing greens.

Carrots are the same. Keep about 2.5 cm of the top and set it in shallow water and you get green leaves, but no new carrot, because the part we eat is the root that has already been cut off.

This group is great for showing children how plants grow, or for a few leaves to garnish a plate. Don’t expect a full crop.

Potatoes and other tubers from the shop

Shop potatoes are often treated with a sprout inhibitor and may not grow at all. An expert answering for the U.S. Cooperative Extension network recommends buying certified seed potatoes that have been inspected for disease, because potatoes bought for eating can carry disease into the bed without showing any signs.

Fresh rhizomes such as galangal, turmeric and fingerroot that still have buds can be planted in soil; the method is in the same lesson as lemongrass above.

The scraps that truly pay off are spring onions and lemongrass. Most of the rest give leaves only.

Common mistakes

• Submerging the whole base. It turns to slime in a few days; cover only the roots.
• Not changing the water. Cloudy, slimy, smelly water rots the plant.
• Keeping it in water forever. Leaves get smaller and paler each round; move it to soil if you want more.
• Waiting for a carrot top to grow a carrot. You only get leaves.
• Buying lemongrass with the base trimmed off. No base, no roots.
• Planting shop potatoes in the vegetable bed. You risk bringing disease into soil you will use for other crops.

Sources

• It Doesn’t Take an Acre: Kitchen Scrap Gardening — WSU Extension Ferry County
• Grow Fresh Food All Year Long — University of Utah Office of Sustainability
• Planting store-bought potatoes that have sprouted — Ask Extension
• 12 Vegetables You Can Regrow From Kitchen Scraps — Farmers’ Almanac