Sadly this is a common problem and you’d be a very fortunate gardener if you never suffered this at some time. Don’t despair, things will improve and once you understand the problem you can start to solve it. So read on to see what you can do about zucchini (courgettes) turning yellow and rotting.
Why Are My Zucchini Turning Yellow?
There are a few answers to this question, some are more serious than others and some have easy cures. So the easiest and obvious one is there are yellow varieties of zucchini and if this is the case you don’t have a problem. If the problem is the zucchini turning yellow and rotting then it needs addressing.
Are Your Zucchini Dying Before Maturing?
This problem has 2 main causes, firstly and most commonly, the plants are not being pollinated. Let’s look at that first, for zucchini to develop the female flowers need to be pollinated by male flowers. Not sure of the difference, don’t worry the section below shows both male and female flowers.
If your question is why are my zucchini shriveling up? Read on.
Male And Female Zucchini Flowers
Here are the male and female zucchini flowers for identification purposes.
Male Zucchini Flowers
These are easy to identify because they have just a thin stem behind them and no fruit. As soon as the flower opens it can be used in pollination.
Female Zucchini Flowers
Even easier to identify because the baby zucchini is visible right behind the flower. As with the male flower, once open it can be pollinated.
How To Pollinate Zucchini
In most cases pollination is done by insects on the search for nectar. So to ensure insect pollination grow other plants to attract the pollinators to your zucchini plants. This is called companion planting and good companions for zucchini are:-
For more information on zucchini companion plants (courgettes) click here. The other way to pollinate zucchini and in some cases the surest way is to hand pollinate.
How To Hand Pollinate Zucchini
Hand pollinating zucchini is a very simple process which requires a gentle touch and a steady hand. There are 2 ways to achieve this, you can pick the male flower and gently push it into the female flower. Or the gentler way which will not cause damage to the plant is to use a small paint brush.
I prefer the childs paint brush as I have had great success using this method in my greenhouse. Plus you can pollinate upto 3 females from one male using this method. For a more detailed explanation on how to pollinate vegetables click the link.
Zucchini Flowers But No Fruit
This can be lack of pollination or it can be the plant is not happy in some way. All plants are affected by heat, moisture, humidity, and nutrients in the soil. If for example it is too hot zucchini will only produce one type of flower either male or female. Without the corresponding partner, no pollination can take place.
It’s always good to grow more than one zucchini and hope that one will produce a male flower at the same time as the other produces a female flower. Don’t be too concerned though because the purpose of zucchini plants is to reproduce and this is done through fruit production. Once conditions improve the plant will balance itself with flowers and zucchini will be the result.
Female Zucchini Flowers Not Opening
Zucchini flowers tend to open early in the morning and close as the day goes on. So for hand pollination early morning is the best time. If you miss a flower opening just wait a few days and another one will develop ( as long as conditions are optimum).
No Male Flowers On Zucchini
This is most likely due to too much heat and the plant not being comfortable. Once conditions improve flower production will improve as well.
As with all heavy feeding plants, zucchini will need extra nutrients throughout the season. The best way to add nutrients is with a fertiliser of some sort and there are many types all claiming to be the best. All you need is a balance of nitrogen, potassium, and phosphorus so if you’re buying fertiliser check the label.
I think home made is best because I grow organically and I know what’s in my own fertiliser. I use home made comfrey tea fertiliser as this gives my zucchini all that they need. To find out how to make comfrey tea fertiliser click here.
If you don’t have access to comfrey a liquid tomato feed can be used instead. I feed my zucchini weekly to keep them in optimum health.
Zucchini Turning Yellow And Rotting Blossom End Rot
The other reason for zucchini to turn yellow and rot is Blossom End Rot . This affects all members of the squash family and tomatoes, peppers, chillies, aubergines (egg plants), and cucumbers. It is caused by a lack of calcium in the fruit and the reasons are not always due to soil deficiency.
Calcium holds the cell walls of plants together and calcium deficiency results in stunted growth, misshapened leaves and yellow, rotting fruit. Adding calcium to the soil is best done long before zucchini plants are grown. Use garden lime and epsom salts about 6-8 before planting your zucchini plants.
For more information on blossom end rot click here.
Blossom End Rot In Zucchini And Epsom Salts
According to the North Dakota State University, adding epsom salts to the soil once zucchini have blossom end rot does more harm than good. However I am a fan of epsom salts and even they concede that it does assist the plant in uptaking nutrients. So it’s worth a try just don’t use too much.
Blossom End Rot In Zucchini and Watering
Another common cause of blossom end rot is irregular watering. If your plants don’t get watered evenly they won’t be able to uptake minerals (in this case calcium) when needed. I have had zucchini that have suffered from blossom end rot that have gone on to produce many fruits after changing my watering regime.
Always remove rotting or decaying fruit and if blossom end rot is the problem look at nitrogen levels not calcium. This is because increased nitrogen causes increased leaf growth and more leaves need more calcium… You see where I’m going with this, the leaves can actually deprive the fruit of calcium.