Which kitchen scraps regrow into food?

Iowa State Extension says green onions, celery, romaine, bok choy and napa cabbage bases will grow new edible leaves, herb cuttings root in water, and untreated ginger can grow new rhizomes. Carrot, beet and turnip tops grow greens but not a new root.

How often do I change the water?

Iowa State says to change the water weekly for green onions, and every 2 to 3 days for celery, lettuce and cabbage bases and for carrot tops, to prevent fungal or mould growth.

Can I plant a sprouting potato from the grocery store?

University of Minnesota Extension advises buying disease-free seed potatoes from a certified grower instead. Store potatoes may be treated to stay dormant, and diseases can stay in the soil for a long time.

Will an avocado pit grow avocados?

Iowa State Extension says you should not expect fruit. It treats an avocado grown from a pit as a houseplant.

Is it safe to eat potato sprouts?

No. University of Minnesota Extension says potato sprouts can be toxic and should not be eaten, and to trim green areas from potatoes and not eat potatoes with a lot of green.

Regrowing Vegetables from Kitchen Scraps: What Works

Regrowing vegetables from scraps is the cheapest garden there is. The root end of a bunch of green onions, the base of a head of celery and a few herb stems can all grow again in a glass of water on a windowsill. It is a good way to stretch fresh food during a long stay at home, and a gentle way to get kids interested in where food comes from.

It also gets oversold online. Some scraps give you a real, repeating harvest; some give you a handful of greens; some only make a houseplant. The details below are from Iowa State University Extension and University of Minnesota (UMN) Extension. I have not tested them myself.

The ones worth doing

Green onions

Iowa State’s method:

Keep the white root ends, roots attached.
Stand them in a jar with just enough water to cover the roots, somewhere warm and sunny.
Change the water weekly.
New shoots should appear in about one to two weeks, and keep coming for a few months.

Snip the green shoots for cooking. Once they reach 4 to 5 inches (10 to 13 cm), Iowa State says you can plant the bulbs in soil, indoors or in the garden.

Celery, romaine, bok choy and napa cabbage

Cut off the leaves you are going to eat, keeping the bottom 2 inches (5 cm) of the base.
Set the base in a shallow dish with about an inch (2.5 cm) of water, in a warm, sunny spot.
Change the water every 2 to 3 days. Iowa State says this prevents fungal or mould growth in the water.
New leaves appear in several days to a few weeks.

Iowa State says the plants are more productive once rooted and moved into potting soil, and can go outdoors in spring. Expect a modest crop of new leaves, not a new full head.

Herbs

Basil, oregano, thyme, sage and mint can be rooted from cuttings, according to Iowa State:

Take 2 to 4 inch (5 to 10 cm) cuttings and strip the leaves from the bottom half.
Stand them in water with no leaves below the waterline.
Change the water once or twice a week and never let the level drop below the roots.
When roots are about 1 inch (2.5 cm) long, pot them in potting soil in a bright spot.

Iowa State notes that roots grown in water are coarser, so the plants may wilt or drop leaves for a while after potting. Steady care helps them recover. A 10-inch (25 cm) pot suits herbs, according to Oregon State University Extension.

Ginger

Iowa State says to choose untreated rhizomes (organic ones are more likely to be untreated), cut them into pieces with 2 to 3 buds, let the cut ends dry for a few days, and plant them flat under about 2 inches (5 cm) of soil. Shoots can take one to two months. Harvest when the plant has gone fully dormant. This one is slow, but it does produce food.

The ones that give greens only

Carrot, beet and turnip tops. Cut off the top 2 inches (5 cm), set it in a shallow dish of water in a warm, sunny spot, and change the water every 2 to 3 days. Iowa State says you can trim the new leaves as they grow, but you will not get a new root.

The ones that are houseplants

Avocado. Iowa State gives a full method for sprouting a pit in water and potting it up, but says not to expect avocados. Grow it for fun.

Pineapple. A rooted top can be grown on as a houseplant. Iowa State says it takes two to three years to mature, a fruit may form, and it will be very small and is not guaranteed.

Potatoes and garlic from the store

This is where scrap gardening most often disappoints.

Potatoes. UMN Extension advises buying disease-free seed potatoes from a certified grower or seed distributor. It says stores may treat potatoes to keep them dormant, and that diseases can remain in the soil for a long time. UMN also warns that potato sprouts can be toxic and should not be eaten, and that you should trim green areas off potatoes and not eat ones with extensive green.

Garlic. UMN advises against planting grocery-store garlic in cold climates, because it is mostly softneck types that may not perform well. Seed garlic for your region is a better bet. My guide to planting garlic in fall covers it.

Iowa State sums it up: if a store potato or garlic clove will not grow, it is more likely due to sprout inhibitors than to you.

Keeping it safe and tidy

Use clean jars and dishes, and change the water on schedule.
Throw out anything slimy or mouldy and start again.
Rinse regrown greens before eating, as you would any produce.

Where this fits

A windowsill of regrowing scraps will not feed a household, but it can keep green onions and a few herbs on hand while you are eating mostly from the pantry. Stir them into meals like one-pot rice and beans or a ramen upgrade, and find more ideas in the recipes.

If you catch the growing bug, a balcony or windowsill garden in pots or sprouts and microgreens on the counter are good next steps. For the pantry itself, start with the plan builder and the food section.