Pumpkin Science: Six Experiments Before the Jack-o-Lantern
Every October, households buy a large, dense, seed-filled biological specimen, cut a face in it, and compost it a week later. Before that happens, a pumpkin will support a genuinely good run of experiments in measurement, density, biology, and decay, all of which are more interesting for using something the kid picked out themselves.
Measure It Before You Cut It
Four measurements to take first
- Mass, on a bathroom scale by weighing yourself holding it and subtracting
- Circumference at the widest point, with a piece of string and a ruler
- Height, stem excluded, then the ratio of height to circumference
- A written prediction of how many seeds are inside
The seed prediction is the important one, because it gets written before anyone can see inside and it gets checked exactly. Most kids guess low by a wide margin, and being dramatically wrong about a number you committed to is memorable in a way that being told a number is not.
Will It Float?
Ask for a prediction, then put the whole uncut pumpkin in a full sink or a bucket. Nearly all of them float, which surprises most kids, because a pumpkin is heavy and heavy things are supposed to sink.
The resolution is that a pumpkin is mostly hollow, full of air around the seed cavity, so its overall density is lower than water despite its mass. Follow up by testing a chunk of solid pumpkin flesh with no cavity, which sinks. Same material, different result, and the only thing that changed is the trapped air.
Count, Sort, and Graph the Seeds
Scoop everything into a bowl and count the seeds by grouping into tens, which is faster and less error-prone than counting one by one. Compare the total to the prediction and to the number of vertical ribs on the outside, which sometimes correlates and is worth checking rather than asserting.
If you have two pumpkins of different sizes, this becomes a real comparison. Does the bigger one have proportionally more seeds, or just more? That requires dividing seeds by mass, which is a graph a middle schooler can make and defend.
Watch It Rot on Purpose
The decomposition observation
- After carving, put the pumpkin somewhere outdoors where it can stay undisturbed for two to three weeks
- Photograph it from the same angle at the same time each day
- Record temperature and whether it rained
- Do not handle it once mold appears, and wash hands after any contact
- Compost or discard it before it fully collapses
A daily photo series of a collapsing jack-o-lantern is a time-lapse of decomposition, and the questions it raises about mold, moisture, and temperature are better than any worksheet on the subject.
Seasonal Science Without the Scramble
The planner slots seasonal experiments into the weeks they belong to, with materials lists that assume you are buying a pumpkin anyway.
Launch Science Kit Planner →Published on October 12, 2026 • 8 min read