Up to 1/3 of what comes home as fresh produce ends up in the compost heap. Half of that can be grown or extended. Everything from Beet greens to Zucchini can be coaxed on in one way or another. You can either extend their production, such as celery or create new crops or seeds.

Vegetables:

(T)ops can be cut up to ½” below their base and rooted in water, then soil, the greens used in salads, with some exceptions like carrots and parsnips, which you can use as a seed source (never eat carrot or parsnip greens!) Biennial plants such as beets, brussel sprouts, carrots, celery, lettucce parsley, parsnip,
(H)earts can be extended by cutting them above the base with enough of the plant to continue it growing, or removing leaves until the remaining part is too small to eat, then using toothpicks to hold it above the bottom of a glass, like an avocado seed until it roots, or planting in warm moist soil. Celery can be grown this way by cutting it two to three inches above it’s base.
Seed Sources are typically from biennials such as carrots, and from squashes and melons that were too mature.  Depending on how friendly you are with your grocer, you may be able to get some of these fruits and veggies that are “past their prime”

With horseradish, you will have to shop for one that has some green sprouts starting on the top, and cut about two inches below this. Let it “heal” (sit indoors away from direct sunlight) for a day or two, then plant it in the ground with just the green (crown) showing.

Beets (T) – Greens, seed source
Carrots (T)(Seed Source Only!)
Parsnips(T) (Seed Source Only!)
Turnips (T) – Greens, seed source
Bok Choy (H) – Greens – (brassica)
Cabbage (H) – Greens, seed source (brassica)
Celery (H) – Greens, seed source
Radicchio (H) – Greens, seed source
Horseradish (T) – root, seed source
Squash/Courgettes – seed source
Melons – seed source

Some lettuce variety have been known to be extended, such as romaine, and – if you can find them – hydroponically grown lettuce heads (with the roots still attached).

Fruits and Grains

You can harvest seeds from fruits and plant them again. Many people have grown citrus trees from their pips, and if you’re lucky you will get fruits from them as well. Apples, avocado, and other trees are long term commitments as are grapes and berries but annual fruiting plants such as tomato, pepper, corn and squash (pumpkin, winter squash, etc.) can be sources of seeds for your garden next season. Always have a backup of your favorite fruits and vegetables, because you cannot tell whether the groceries you have bought are hybrids with little or no viability. Grains I have never tried, but there have been successes with them. Be careful, nowadays with law-suit happy Mega companies, it will be better (and may be healthier) to source local seeds.
A partial list includes: Squash, Melons, Tomato, Peppers, Corn, Amaranth, Quinoa, Wild rice

Propagating Down Under – or – I’ll Take The Tube(r)

Potatoes, Jerusalem artichokes (which are American native plants), ginger, yams, sweet potato can all be grown if they’ve been kept long enough under the proper conditions. We typically have potatoes that begin to sprout. I put them in the garden, away from my favorite (King Harry) potatoes just in case there is some type of disease, and typically they get eaten by the bugs that King Harry’s are well defensed against (King Harry potatoes have hairy leaves, they are not hairy potatoes!). Jerusalem artichokes are also easily grown, and will proliferate, so choose their homes wisely – they will be hard to evict once they are established.
Yams and sweet potatoes can be treated just like potatoes, or you can put one into a moist container that sits in a warm area, out of direct sunlight, and wait for the sprouts to show. Put the sweet potato into a place that gets strong sunlight, and wait until you have three leaves on a “slip”. from this point, you can rub the slip off of the plant gently with your thumb, and place it into some soil so it will root. The sweet potato will continue to create slips until it is exhausted. Note: some sweet potatoes only take weeks to accomplish this, others take months.

Bulbs (onion, garlic, leeks)

Have you ever left ½ an onion in the fridge, only to find the center growing and the outer edges rotting? Time to place that in the soil and get it to grow! You can get it to seed this year (if it’s early enough in the season) and plant the seeds next year.
You can do the same with garlic cloves. Simply take the small cloves that are not worth crushing and place them pointy side up into the soil. You can either get garlic sprouts, or gather the seeds for next year.

Dried Beans Beans (all types)

There are a multitude of dried beans in most grocery stores. They are often viable, too. If you use them regularly, take about ten of them and fold them into a wet paper towel. Put the towel in a ziplock bag and wait for seven to fourteen days to see if they sprout. If they do, you can plant them out and harvest your own beans to dry by the end of the season. Lentils, mung beans, pinto beans chick peas, black beans – they all can be cultivated. Split peas won’t work – or if they do, you’ll only get half a crop… (kidding).

Herbs

Most herbs will not do well as cuttings, and it’s best to start these from seed. Exceptions being any herbs that come with roots, such as lemon grass, and ginger. These can be propagated by placing them into potting soil in a slightly warm location and keeping them moist.

For a complete book of groceries you can grow from your groceries, check out Don’t Throw It, Grow It!: 68 windowsill plants from kitchen scraps.