Can you use a pumpkin as fertilizer?

Halloween is coming soon and many people will have carved pumpkins in their homes. But what can you do with the pumpkin when Halloween is over? For most people it just ends up in the organic waste or on the compost, where it sadly rots away. Would be nice if you could also use pumpkin as fertilizer. That way you can create new life with the leftovers from Halloween.

To answer your question in a nutshell: Yes, you can use pumpkin as fertilizer if you dry it first. You can find out the details now.

If you're more interested in substrate for closed terrariums, read on here.

Pumpkin fertilizer is rich in nutrients

Pumpkins (Cucurbita) are herbaceous plants that can bear small, large but also perfectly huge fruits. These fruits are also called shell berries. Especially popular for Halloween are, for example, the giant pumpkin (Cucurbita maxima) and the garden pumpkin (Cucurbita pepo).

Giant pumpkin Cucurbita maxima is suitable as fertilizer for terrariums
A giant pumpkin. Source: KENPEI on Wikimedia Commons, CC BY-SA 3.0

Pumpkins, by their size and hefty flesh alone, are stuffed full of nutrients that would be super for a flower bed or terrarium. Over their lifetime they take up nitrogen, phosphorus and potassium in particular. These, of course, can become helpful for other plants later on. However, you have to keep in mind that some plants cannot tolerate these nutrients at all.

This is bad for Venus flytraps, for example. They and many other plants from bogs or swamps have specialized specifically to get by without many nutrients in the soil. In the case of Venus flytrap, too much nitrogen will cause their fancy trap flowers to not grow as large or, in the worst case, even fail to grow at all. So in any case, you should find out beforehand for which plants you should not use nitrogen, phosphorus or potassium.

How to turn pumpkins into fertilizer

You can theoretically just mix the pumpkin in with your soil and hope it works out. However, this is not the best method. A soggy pumpkin that has been sitting around your house or outside for several days is the perfect breeding ground for mold. Mold is super fond of attaching itself to plants and robbing them of nutrients. So if you were to fertilize your plants with damp pumpkin, it's more of a crapshoot.

It is much better to dry your pumpkin first to neutralize all bacteria and fungal spores. To dry your pumpkin, first cut it into small pieces that you can place on a baking sheet. You don't need to be sparing with the space on the baking sheet. You can even stack the pieces as long as they still fit in your oven. As they dry, they lose a lot of water and become much smaller.

For the actual drying, set your oven to approximately 50°C to 60°C (about 120°F to 140°F). It's best to use convection, but upper-lower heat is of course also okay. Now let your pumpkin pieces dry for three to four hours in the oven. When they are dry as dust, you have two possibilities to use them as fertilizer

Burying whole pieces

You can choose a place in your garden or terrarium and dig a hole of about 20 cm to 30 cm (8 to 12 inches) where you put the pumpkin pieces. Then bury them and let the worms eat them there. You can't put a plant there right now and should wait until spring. By then, the worms in the soil will have eaten so much of your pumpkin that they will have left a lot of natural fertilizer and also a lot of passages for better ventilation for your plants.

Pulverize and sprinkle

The other option is to put the pumpkin in a plastic bag right after it dries and pulverize it with a wooden mallet. You don't need to bury this pumpkin powder, you can sprinkle it directly on top of the soil of your plants. This is better than the first option because then you don't have to restructure and change your terrarium again.

Here again, very briefly summarized:

  • Cut pumpkin into pieces
  • Place pumpkin pieces on baking tray
  • Dry in the oven for 3-4 hours at 50°C to 60°C (120°F to 140°F)
  • Bury whole pieces under flower bed
  • or pulverize the pumpkin pieces and sprinkle them

Summary

Pumpkin makes a wonderful fertilizer when you're done using it for Halloween. You should not use it wet, but dry it in the oven first. When dry, you can either bury it in whole pieces and plant a plant there later, or pulverize it and sprinkle it over your terrarium or flower bed. Since pumpkins are rich in nitrogen, phosphorus and potassium, you should check beforehand if your plants can tolerate it.

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