Under the right conditions, the vegetables in your fridge can start growing again, thanks to the presence of special cells called meristematic cells. Experiment with various plants to find out where these cells are located and what it takes to make them grow.
One or more of the following: Head of lettuce, bok choy, or celery (not just the individual leaves or stalks); scallions (aka green onions); root vegetables such as carrots, beets, turnips, or radishes, with their tops attached; leafy stems of basil or mint; whole potatoes
Glasses or transparent plastic cups (so you can see through)
Magnifier (or zoom function on a cell phone camera)
Optional: digital scale
Each type of vegetable will be treated slightly differently, but in all cases the goal will be the same: Separate the different parts of the plant, provide each part with water and light, and see what grows.
Lettuce or bok choy: Cut the leaves off the bottom of the head, leaving a few centimeters where each is attached (click photo to enlarge). Place a few of the leaves in water. Place the remaining piece of the head of lettuce or bok choy in a shallow dish of water, bottom-side down.
Celery: Cut off the stalks about 1 1/4 inches (3 cm) from the bottom of the head. Place a celery stalk in a glass of water. Place the bottom of the head into a shallow bowl of water.
Scallions: Cut the green part from the white part. Place each piece in a glass of water, roots down for the white part; cut-edge-down for the green part.
Root vegetables (carrots, beets, turnips, radishes): Cut the top (where the leaves are attached) from the vegetable itself. If there are still leaves attached, cut them off, leaving about 1/4 inch (1/2 cm) of each leaf’s stem. Place the top in a shallow bowl of water. Stick three toothpicks through the sides of the root, and balance it in a glass of water, root-tip down. Place a leaf (if you have one) in a glass of water. (Click photos to enlarge.)
Leafy stems (basil, mint): Recut the bottoms of the stems. Remove the lower leaves (so no leaves will be submerged), and place the stems in a glass of water. Put a few stemless leaves in a small glass of water, stem-attachment-side down.
Potatoes: Cut the potato into a few pieces, making sure that some have eyes (those little warty spots) and some don’t. Put the pieces in a dry bowl. Because potatoes already contain a lot of water, you don’t need to add any extra.
Put your vegetables in a sunny, airy place. Add water if it becomes low, and change the water if it becomes cloudy or colored.
To Do and Notice
Keep your vegetables in the sun for at least a week, and check them daily to look for changes.
What new growth do you notice? What structures do you see growing? Are there new leaves, stems, or roots?
Use your magnifier or the zoom function on a cell phone camera to look for small changes. Where do you see growth? Which parts don’t seem to grow?
Keep watching your vegetable scraps over a few weeks. Do any stop growing? What changes do you notice? If you have a digital scale, you can weigh your plants over time to track their growth.
What’s Going On?
Unlike people, plants have a special ability to grow continuously throughout their lives. Most will continue making new roots, stems, and leaves until they die.
The continuous growth of plants takes place thanks to meristems, perpetually embryonic plant tissues made up of specialized cells called meristematic cells. Often compared to the stem cells found in animals, meristematic cells can continuously replicate themselves and are undifferentiated, meaning that they have the potential to turn into all different types of plant tissues.
There are several different types of meristems: Some make stems and leaves, some make new roots, some help the plant’s stems grow outward, and some do all three. Meristems aren’t distributed equally around a plant; instead, they’re located in small, distinct compartments, often at the tips of shoots and roots.
The location of any given meristem determines the type of tissue it can become. For example, you probably noticed new roots sprouting from the meristems found in the bottoms of your root vegetables, as well as the bottoms of lettuce, bok choy, and celery heads, and the stems of mint or basil. Meristems capable of making leaves are the source of any leafy growth you noticed in the tops of your root vegetables, or at the tops of your severed celery and lettuce heads.
Some vegetable parts probably didn’t show any new growth. Lettuce and herb leaves separated from their heads or stems don’t contain any meristems capable of sprouting new stems or roots.
At some point, despite the presence of meristematic cells, your vegetables will probably stop growing. While you may have supplied them with sunlight, water, and air, the main things that plants need for growth, they will eventually run out of other essential nutrients, such as nitrogen, phosphorous, and potassium. As anyone who grows vegetables hydroponically (that is, in water without soil) can tell you, these essential nutrients must be added to the water for robust growth.
To keep the growing going, take the vegetables that have sprouted roots (such as herbs, celery, or potatoes) and plant them in soil outside for eventual harvest.
Try designing experiments to investigate which factors are important for different vegetables to regrow. Can your veggies grow without light? Cover a plant with foil or place in a dark cabinet to see. Can they grow in the cold? Put them in the fridge and see what happens. Can they grow without water? What happens if you supply some extra nutrients by adding a little liquid fertilizer to the water?
Experiment with other vegetables: The ones we’ve suggested will usually grow reliably, but put anything you want in a dish of water and see if it will grow. What mighty meristems can you discover in your fridge?
Check out this episode of Hungry for Science to see how to regrow green onions and potatoes.