How to grow a plant from seed with your kid (and measure it as it grows)

There's something magical about watching a tiny seed turn into a plant, especially when you planted it yourself. Growing a plant from seed teaches patience, responsibility and real biology, all from a cup on the windowsill.

Why it's great science

In the Next Generation Science Standards, used by many U.S. schools, second graders plan and carry out an investigation to find out whether plants need sunlight and water to grow. A seed cup at home is the same science, and your child gets to take care of a living thing while they learn.

Measuring the plant connects to math, too. In schools using the Common Core standards, second graders learn to measure length with tools like rulers.

Skill 1: Plant seeds in a cup and water them

1. Fill the cup with soil, almost to the top.
2. Push two seeds in, a finger deep.
3. Water until the soil is damp.
4. Put it in a sunny spot.

Seeds that grow fast and big are best for kids: beans, peas, sunflowers, radishes and squash usually sprout within a week or two. Check the seed packet for planting depth and how many days to sprout.

Poke a drainage hole in the bottom of the cup and set it on a saucer. Soggy soil can rot seeds.

Try a clear cup, or plant a bean against the side of a clear cup with a damp paper towel. Then your child can watch the roots grow, too.

Skill 2: Measure the plant every few days

1. Measure from the soil to the top.
2. Write the date and the height.
3. Measure again every few days.
4. See how much it grew.

A simple growth table:

Measure the same way each time: same ruler, from the soil to the very top. Kids can also draw the plant each time, and later line up the drawings like a flipbook.

Use centimeters if you can. Plants grow fast in centimeters, which makes the numbers more exciting than ¼ inches.

The challenge: grow it to its first true leaves

The mastery goal is to grow a plant from seed to its first true leaves.

1. Water it when the soil feels dry.
2. Keep it in the sun.
3. Watch for the first tiny leaves.
4. The next leaves to grow are true leaves.

What are true leaves? The first leaves to appear are usually seed leaves, which often look different from the plant's grown-up leaves: round, smooth or oddly shaped. The leaves that come next are the true leaves, shaped like the leaves the plant will have from then on. A bean's first leaves look quite different from the true leaves that follow.

The University of Minnesota Extension explains that seedlings don't need fertilizer until they have several sets of true leaves, which is a clue that true leaves mark a new stage in the plant's life.

Troubleshooting

• Tall, thin, floppy seedling? It's probably reaching for light. The University of Minnesota Extension notes that too little light causes tall, thin stems, and that seedlings do much better under grow lights than a window alone. A sunnier window can help, or a desk lamp with an LED bulb nearby.
• Nothing sprouted after two weeks? Some seeds don't sprout. That's why we plant two. Try again, and talk about what might have happened.
• Moldy soil? Probably too wet. Let it dry out a bit between waterings.

Keep the soil moist, not soaked, while seeds are sprouting, the Extension advises.

Turn it into an experiment

Once your child has grown one plant, they're ready to ask a real science question: "What happens if a plant gets no sunlight?" Grow two cups the same way, and put one in a dark cupboard. Change only one thing. The NGSS assessment for this standard focuses on testing one variable at a time, which is the heart of a fair test. (More in running a fair test.)

Make it a quest

In Family Quests, this is the Grower skill. Practice quests are plant seeds in a cup and water them and measure the plant every few days, and the mastery quest is grow a plant from seed to its first true leaves. A photo of the plant next to the ruler makes great proof, and any photo is deleted once you've reviewed it. Start free.

Next: teach your kid to run a fair test, or go back to observing nature.