How to ripen green tomatoes

So, you’re looking at your green tomatoes growing in the garden and thinking: 'I’m not sure these are going to ripen before the autumn frosts.'

Well, worry no longer, because we have the best advice on how to ripen green tomatoes, so you can enjoy all of the fruits of your summer labours.

What makes tomatoes turn red?

In order to ripen green tomatoes, it’s useful to understand why they turn red. It’s to do with a naturally occurring hormone in lots of fruits called ethylene. Fruit releases it when it is nearing maturity. And it is this hormone that encourages them to ripen. It helps turn them soft, sweet and succulent and tempting enough to eat.

One of the other effects that ethylene has on tomatoes is that it turns tomatoes from green to red. The bright colour makes tomatoes even more tempting to be eaten, which helps them naturally distribute their seeds so they can reproduce.

For ethylene to be produced, plenty of sunshine and warm weather is required. One of the downsides of living in the UK is that our summers can be somewhat temperamental. Tomatoes originate from central and South America, in climates with longer and warmer summers.

In Europe, tomatoes often bask in the warm Mediterranean sun but don't do quite as well in our cooler and sometimes inclement summers. 

Our short summers, and reducing daylight hours as the season progresses, means tomatoes struggle to ripen and turn red in the UK from mid-August onwards.

However, despite our cooler summers, there are steps we can take to ripen green tomatoes.

How to ripen tomatoes outdoors

Ripen on the vine first

Ideally you want to try to ripen the tomatoes outdoors first on the “vine” (sometimes called “bine”). This is because tomatoes ripened outside in the late summer sun are said to taste better.

Whether this is true or not is a personal preference, but it's worth trying these tips below before picking them green and taking them indoors.

1. Remove any remaining flowers 

These take up a lot of energy from the plant. It is better to divert this into ripening the remaining fruit, as the flowers won't have time to develop into tomatoes.

2. Prune off the top of the plant

Cut through the central stem above the highest truss of ripening tomatoes with secateurs.

You want all the energy of the plant to go into fruit ripening, not into growing any higher. And the top part of the plant will also shade out the tomatoes.

3. Trim away surplus foliage and branches

In addition to removing the top of the plant, you can also remove sub- laterals and other branches not supporting any fruit. They are no longer needed for fruit production.

4. Reduce watering

Another trick to ripen green tomatoes is to gradually reduce down the watering. This slightly stresses the plant and gets it to think about ripening its seed so that its seedling may continue. There is nothing like inducing mild panic within a plant to encourage it to ripen its fruit quickly.

Don’t just stop watering suddenly, though; instead, gradually slow down the amount you give them. Not only will it help your green tomatoes ripen, but it will also help you conserve water.

5. Use a tomato feed to boost colour

If you have been feeding your tomatoes with a high nitrogen product then you should stop at this time of year. This is because nitrogen promotes the growth of green leaves and shoots.

Instead, once a week you could use a specific tomato feed, which is usually higher in potassium. This encourages fruit to develop colour and flavour and therefore ripen green tomatoes.

6. Bring them indoors

Finally, as the sun slowly sinks on our summer and we sense the dip in temperatures, it might be necessary to harvest those stubborn green tomatoes and bring them into the house.

The extra heat from the house will encourage green tomatoes to ripen naturally and protect them from blight and frosts.

Sometimes just leaving them on a warm sunny windowsill will speed up the ripening process. It can take a few weeks, but as long as the tomatoes are still firm and in good condition, be patient.

How to ripen tomatoes indoors

My favourite trick to get green tomatoes to ripen is to place them in a bowl of ripening bananas. They too will be producing ethylene and will help the tomatoes ripen. I cover the bowl with a tea towel to trap the ethylene beneath. In a few days they will hopefully be as red as a billiard ball. Just be aware that you may also end up with some very ripe bananas.

Monty Don's blog has a variation to my tip about ripening green tomatoes after picking them – put them in a drawer with a banana. If you can’t spare any drawers in your house, then just pop the green tomatoes in a paper bag with bananas. 

Finally, if you find that your green tomatoes are particularly stubborn and won’t even ripen indoors, it’s not the end of the world. After all, green tomato chutney is delicious and there are plenty of recipes out there to inspire you. Try BBC Good Food's green chutney recipe.