How to keep your pumpkin from rotting

This article was originally featured on The conversation.

For many Americans, pumpkins mean fall is here. In anticipation, cafes, restaurants, and grocery stores are launching their pumpkin-flavored promotions in late August, a month before fall officially begins. And shoppers are starting to buy fresh decorative winter produce like pumpkins and squashes in the hot, muggy days of late summer.

But these fruits — yes, botanically, squashes and squashes are fruits — don’t last forever. And they might not even make it to Halloween if you buy and carve them too early.

As a plant pathologist, gardener, and self-proclaimed pumpkin fanatic, I managed to grow boldly, carve properly, and keep these iconic winter squashes in their bloom through late October. Here are some tips that can help your epic carvings survive the Day of the Dead.

Choose a healthy pumpkin and transport it carefully

This may seem obvious, but buy a pumpkin the same way you shop in the produce department. Whether you plan to carve them or not, choose pumpkins that aren’t damaged, dented, or diseased. Is the stem loose? Is there a clear break in the bark? Are there water soaked spots on the outside?

Post-harvest diseases—those that appear after the squash is removed from the vine—can appear anywhere between the field they were grown in and your entry level. A bruise or tear allows opportunistic fungi, bacteria, aquatic fungus, and small insects to enter and colonize your gourds. The flawless bark and the intact stem ensure a longer shelf life of your valuable pumpkin.

The journey home also plays a role. Most of us transport pets, children, muddy hiking boots, and groceries in our cars, turning our vehicles into giant petri dishes that harbor common mold and bacteria. Some of these microbes could colonize your unsuspecting pumpkins.

Secure your pumpkins on the way to your home so they don’t suffer bruises or broken stems. My family often uses seat belts to protect ours. When you are at home, do not carry your squash by the stick as this can cause breakage, especially if it is large and heavy.

Keep them clean and dry

Squashes spend most of their lives in fields and thrive in soil teeming with fungi, bacteria, aquatic fungus, and soil-dwelling animals like nematodes, insects, and mites. Removing these organisms and any eggs they may have attached to the rind of your squash will help preserve it.

To get rid of them, wipe down your pumpkins, preferably with a bleach wipe or two. This is especially important if you plan on carving them: piercing the dirty rind with a sharp tool will introduce those eager visitors deeper into the heart of your pumpkin. Also make sure to use clean tools. Microbes can reside and multiply on small amounts of pumpkin scraps stuck in the teeth of dirty carving knives.

Even if you don’t carve your pumpkin, it’s a good idea to wipe it down as it may have small dents or cracks that are easy to miss.

ls. When you scoop out the squash’s innards, carefully inspect the inside walls for soft rotten spots or darkened tissue that may have been colonized by bacteria, fungus, or aquatic mold before or after harvesting. Sick pumpkins sometimes give off a repulsive smell, so use your nose too.

If you encounter these carving problems, you should try carving another pumpkin. You can also paint your pumpkins instead of carving them, which eliminates the need to look inside.

Some online tutorials and YouTube videos recommend thinning the walls of pumpkins to allow candle or LED light to pass through. But if you make the walls too thin, your jack-o’-lantern’s fangs will become incurved flaps of skin as the pulp dries and deforms. A toothless jack-o-lantern doesn’t scare anyone.

Another benefit of keeping thicker walls is that you can try a 3D carving. It sculpts the surface of the pumpkin as if you were carving a piece of wood without breaking through the skin and can produce dramatic results.

Some people soak their carved pumpkins in diluted bleach or vinegar water after they’re done. But this technique is a double-edged sword: adding more free moisture to your masterpiece invites wind-blown mold spores and rain-splattered bacteria to colonize it. However, applying a light coating of petroleum jelly or vegetable oil to all exposed parts can extend the shelf life of your sculpted pumpkin.

Protect your creation

October is a wet month with frequent rains in many parts of the US Rain falling on your jack-o’-lantern will invite any mold in the neighborhood to settle in or on it. For this reason, I recommend keeping your pumpkins on a covered porch or displaying them in a window from indoors.

It’s okay if mold grows in it, as not all fungi cause soft rot — diseases that produce wet patches that spread, become mushy, and turn black. If a squash becomes excessively moldy on the inside walls, move it outside to avoid producing a lot of spores inside your home.

If your pumpkin starts to get moldy and break down, don’t throw it in a landfill. Put it around the neighborhood for your deer or on your compost heap. Or find a spot in your garden where you can watch it deteriorate over time until it turns back to soil in time for next year’s pumpkin patch.

Matt Kasson receives financial support from the National Science Foundation, the National Geographic Society, and the US Department of Agriculture. He is an active member of the Mycological Society of America and the American Phytopathological Society.