Why Cucumbers turn Yellow

Yellow cucumbers trailing from the vine may well be an interesting sight, but the question remains – why they turn yellow in the first place!

Other questions soon follow, such as are yellow cucumbers still edible? and why indeed do they also tend to me misshapen or narrow at one end – or show signs of rotting.

These are all issues that any gardener may face when growing cucumbers in particular. However they are issues that can also affect tomatoes, water melons, squash, and peppers.

yellow cucumber growing on vine hanging from a framework of horizontal canes
This yellow twisted cucumber growing in my polytunnel is typical of over-watering by my enthusiastic sister! The cucumber itself will be removed and ‘relocated’ to the compost heap.

Why do cucumbers turn yellow?

There are several reasons why this happens, but it is mainly down to growing conditions in the end – usually a shortage of calcium and other minerals brought on by over-watering the plant.  

Things that can cause a yellowing of the cucumber as well as the fruit rotting at the end (blossom end rot article) include…

  • Over-watering or irregular watering of the plant.
  • The cucumber may be over-ripe and the chlorophyll that produces the green colouring is fading away.
  • The cucumber plant may be infected with a virus such as IpomovirusOpens in a new tab.
  • Lack of nutrients in the soil, particularly calcium that can result in yellowing and blossom end rot.
  • The cucumber may be a yellow variety such as Yellow Submarine, Lemon Yellow, and Salt and Pepper!
yellow cucumber on plant hanging between cane structure
Another cucumber turning yellow on the plant

Overwatering issues:  This is a major cause of rotting cucumbers and affects tomato plants and zucchini plants in particular. The problem is that irregular or overwatering causes the plant to suck up as much water as it can, diluting the mineral content in the process.

This is usually because the grower is allowing the soil to dry out too much before watering the plants. The plant responds in desperation just as I would if I were dying of thirst – with a huge intake of water on impulse!

Overwatering is particularly bad with tomatoes as it can also cause them to split or burst on the vine as a result of too much water consumed too quickly.

The solution to this is simple. Water frequently but in measured amounts. Keep the soil at the base of the plant moist – but not wet! Cucumbers in particular, like the base around the stem of the plant to be on the dry side rather than wet.

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Composting, Square Foot Gardening, Root Cellar Construction, Keyhole Gardening

Over-ripe cucumbers turn yellow to let you know that they are over-ripe! These can be bitter to the taste and really not edible – not even in a cucumber soup which I know from experience will be extremely bitter.

The yellowing effect is simply the chlorophyll that colors the green cucumber leaching away as the plant ages.

Are yellow cucumbers poisonous? Strictly speaking they are not poisonous, but most people would agree they are most unpleasant to eat and could result in a tummy upset to say the least!

A Cucumber virus such as Ipomovirus (also called cucumber vein yellowing virus) can result in yellowing cucumbers and the eventual dying away of the plant as a whole.

It is known to be spread by the whitefly Bemisia tabaci and so a close watch and an effective pest control regime will help stop this from happening.

However if the plant is already infected then I have found that the removal and destruction by fire is the only effective ‘cure’ for this viral infection.

3 examples of cucumbers that have gone yellow in color. Sitting in a row on the polytunnel floor
More examples of yellowing cucumbers picked from my overwatered vine.

A Lack of nutrients in the soil may not be what it seems like! In fact there can be plenty of soil nutrients or minerals – but the overwatering dilutes them to a level where they are no longer efficacious.

However, that said. If you are convinced the watering is fine but your cucumbers are turning yellow before their allotted time, then try adding calcium to the soil (powdered eggshells is excellent for this) as a lack of calcium is the major cause of this and blossom end rot in many cucurbits and tomato plants.

Blossom end rot is easily identifiable by the plant rotting away at what was the flowering end of the plant.

Yellow cucumbers are not always as a result of infection or lack of nutrients or indeed overwatering – they may well be a variety that is yellow by design!

So before doing anything radical – check that you have not planted a yellow variety – even by mistake.

I have in the past found that some seed packets are not accurately printed out, and have grown vegetables that have not been what it said on the packet.

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Some popular yellow cucumber varieties include..

  • Gele Tros  – large Dutch yellow cucumber.
  • Yellow submarine (Cucumis sativus) almost seedless 8inch cucumbers.
  • Lemon yellow – a round tennis-ball size mild flavour cucumber.
  • Salt and pepper variety – A hybrid cucumber small and squat with small black spikes on a yellow skin.

What to do with cucumbers that have turned yellow.

Whilst they are not poisonous as mentioned earlier, they are extremely unpleasant to eat – even if included amongst other veggies.

However they can be made beneficial by chopping them up and adding to the compost heap as ‘green’ material. As they are a rich source of nitrogen they will add real value to the compost.

If you are going to add to the compost heap, then it is better to mix them into the existing compost rather than leaving them on the surface as they may well attract vermin and flies as they decompose.


Best Selling author of several no-dig gardening books, James has over 40 years of gardening knowledge and experience to share with like-minded gardening enthusiasts.

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