Harvesting delicious vegetables from the garden is the goal of all work for many hobby gardeners. Unfortunately, the joy of this is often spoiled by bitter zucchini, pumpkins or cucumbers. Many cucurbits can form these substances, mostly through mutation or crossing with wild varieties. The bitter substances can even be toxic in high concentrations, so much so that you can die from them. Luckily this is very rare.

Factsheet on cucurbits

  • Flowering plant family
  • Mostly herbaceous plants with tendrils
  • About 800 species
  • Most important for cultivation: garden squash, cantaloupe, cucumber, watermelon, zucchini
  • Occur worldwide
  • Only the bryony genus is native to Germany
  • Mostly taproot that goes very deep
  • Large, showy flowers, mostly unisexual
  • Many fruit shapes in different sizes
  • Mostly lots of seeds
  • The bitter substances from the group of cucurbitacins are typical for pumpkin plants
  • Sometimes also contain triterpene saponins
  • Seeds rich in oils
  • Pumpkin plants like it warm, so they grow quickly

The bitter substances

Many pumpkin plants contain bitter substances from the cucurbitacine group. These are included in the fruit to deter natural predators, a simple defense mechanism. If you ingest too many of these bitter substances, it can lead to nausea, vomiting and diarrhea. In individual cases, death can also occur if the concentration was too high. The bitter substances were bred out of pumpkin plants that are sold in the supermarket. The responsible gene has been switched off. However, since it is still there, it can also be switched on again, for example by spontaneous mutation or by crossing with wild types. This danger usually exists when hobby gardeners use their own seeds.

Anyone who notices a strong bitter taste when eating a cucurbit should spit the food out and stop eating. This bitter taste is a clear warning sign. Even slightly bitter-tasting pumpkin plants should not be eaten, because the proportion of cucurbitacins varies greatly. This is probably also due to the weather conditions during the growth and ripening period. The bitter substances are not lost even when heated. They don’t go away with cooking, frying, or baking.

Tip: There are no bitter substances in supermarket vegetables. These can be eaten without any problems.

What causes the formation of bitter substances?

There are different possibilities. On the one hand, the weather conditions are decisive. In many cases, heat stress is the reason for the formation of the toxic cucurbitacins. Great heat, constant sun exposure and lack of moisture are a bad combination for cucumbers, melons, squashes and zucchini. Another reason is inedible ornamental gourds nearby. Bees and bumblebees make no difference in collecting nectar and pollinate the ornamental plants just like the edible ones. The result can be a bitter fruit. However, these cases are rather rare. More often, reverse mutation results in inedible fruit. The bitter genes were bred out of the plants. They sometimes reactivate, albeit generations later.

Note when mounting

If you want to grow pumpkins in the garden yourself, you should consider a few things to avoid gene activation of the fruit.

  • Don’t grow edible gourds and ornamental gourds too close together!
  • Do not use self-harvested seeds for sowing. It is better to buy seeds.
  • Taste the harvested vegetables before processing and eating them!
  • Spices can mask the bitter substances
Note: There are people who cannot perceive bitter substances properly. If you don’t like bitter taste, you have to be particularly careful if you want to eat pumpkin plants that you have harvested yourself. It’s best to let someone taste it first.

Frequently Asked Questions

What to do if you are poisoned by the bitter substances in the cucurbits?
If severe digestive disorders occur, i.e. bloody diarrhea with colic pains, plus increased salivation, sometimes associated with tachycardia and headaches, you should see a doctor immediately. Don’t experiment yourself. Only gastric lavage, taking charcoal and often an infusion can help here.

Are all ornamental gourds inedible?
Not every ornamental pumpkin is inedible. Rare varieties of gourds are often sold as ornamental gourds, but there are none at all. They are edible. If you are not sure whether the pumpkin can be eaten, you should simply try it. A simple taste test brings clarity

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