Our Essential Guide: How To Grow Chillies In A Greenhouse

Our Essential Guide: How To Grow Chillies In A Greenhouse

It's never too soon to start planning your growing, and with a greenhouse at your disposal, you can start sowing your chillies as early as February.

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There are over 4000 chilli varieties of chilli in the world with a phenomenal range of flavours and heats, from fun and sweet to fierce and fiery. In the UK, they are a popular plant to grow in gardens, greenhouses and window sills because they are a relatively low maintenance crop. Originating in hot climates, chilli plants prefer warm and sunny positions to thrive; making a greenhouse an ideal place for them.

The most popular chilli plants to grow in the UK include the Scotch Bonnet, Jalapeno, Tabasco, Cayenne and Habanero varieties.

picking fresh chillies by hand

The wonderful thing about chillies is that you can do so much with them. The obvious choice is adding them to your favourite curry or chilli con carne recipe but aside from the myriad options available with the fresh fruit, you can also dry them out which gives you endless other ways you can use them. So unlike other vegetables or fruit you can grow in a greenhouse, you needn't worry about growing too many chillies; you will find a use for them!

The growing cycle of a chilli (in a greenhouse)

January February March April May June
Sow Sow Sow Grow Grow
July August September October November December
Grow/Harvest Harvest Harvest Harvest

NB: Cycles like these are always a best guess, and with a good environment, it is possible to sow in January and harvest even into December!



Most chilli plants should be sown between February and April but some of the hotter varieties could benefit from being sown even earlier to allow extra time to grow and mature. Fill some pots with good quality growing compost (a loose structure is best), flatten it out and place the seeds on top. Cover them with a thin layer of compost or Vermiculite. The seeds will germinate over a few weeks and transplant them individually into 9-10cm pots when two true leaves appear.

Ellen Mary checking on Chilli plants in her Rhino Greenhouse


Nurturing the chilli plants

In late April early May, once the roots have filled the 9-10cm pots, the chilli plants should be ready to be placed into their permanent position. If you are keeping them in containers in the greenhouse, transplant them into 20-25cm pots, filled with quality general purpose compost (read our compost guide here) and place them in a sunny spot of the greenhouse. Chilli plants benefit from a supporting stake or bamboo cane - get this in position early so as not to disrupt the roots later on and begin tying it regularly to keep the stem from flopping and breaking as it grows. Once they get to around 20cm tall, you can start pinching out the growing tip and side shoots to encourage a better crop.

Make sure the plants are well watered, especially in a greenhouse; twice a week during the warmer months. Feed them with general liquid feed when the first flowers appear to get a bumper crop. It is also worthwhile spritzing the leaves with water too as this will keep away pests such as red spider mites.

Top tip: The plants need to pollinate in order for the fruits to grow and this is difficult to occur naturally in a greenhouse, where there are fewer pollinators To encourage pollination, the pollen within the flowers needs to be released and spread around the flower head. You can enable this release of pollen by gently rubbing the flower heads with a finger or small soft paintbrush.

The chilli peppers will go from green to red over the course of the summer. Generally, the longer you leave them and the redder they get, the hotter they become. Harvesting will start in June to July and usually finish in October.

Many people think chillies are annual plants, but they are in fact short-lived perennials. Given the right care and attention, they can continue to fruit for several seasons. The UK climate isn’t ideal for them and the cold usually kills them off, but it is possible to keep them safe and healthy until the spring and get an earlier crop than you would from a less mature plant.



Much like tomatoes and other fruits, you can save some of the seeds from your chilli plants for next year.

  1. Scrape the seeds out into a sieve and remove as much of the gelatinous layer around the seeds as possible under running water .
  2. Empty the seeds onto two layers of kitchen paper and spread them out to dry. If you know the variety, write it down on the kitchen paper (if you know it!) and leave to dry for a couple of days.
  3. You can then simply fold the paper and store in a labelled envelope in a cool, dark place until next February


What causes heat in chillies?

Chillies contain a chemical called Capsaicin (Cap-say-a-sin) which causes the spiciness. The chemical is an irritant for mammals and causes a burning sensation when it comes in contact with tissue. Some people say there are some medicinal benefits of Capasicin, including reducing insulin spikes in diabetes and relieving topical pain but large amounts of the chemical can cause huge discomfort and nausea.

The hotness of a chilli pepper is measured on the Scoville Scale. For context the common Jalapeno pepper is 2500-8000 Scoville Units, the Scotch Bonnet 100,000 - 350,000. The hottest chilli pepper in the world is called the Carolina Reaper and measures at 1,500,000+ Scoville Units making it is 200 times hotter than the Jalapeno. The Carolina Reaper was developed by crossing a Red Habanero and a Naga chilli.

Carolina Reaper Chilli - the hottest chilli in the world


Preserving chillies

A great way to make use of your bumper crop of chillies is to dry them out or freeze them. By drying them out, you then have numerous opportunities for trying chillies in different ways and, as a result of the preservation process, much longer to try them all out.


Drying chillis hung from a wooden bannister

How to dry chillies

Air drying chillies is simple and can be done inside your greenhouse or home. Not only is it a great way to use the chillies up, they look striking too.

  1. Pick the chillies ensuring that you pick them with a 2-3cm stem.
  2. Bunch them together and tie string around the stems.
  3. Hang them from something like a curtain pole or a string line hung in the eaves of your greenhouse.
  4. They will take a few weeks to dry, depending on how warm it is.

You can also dry chillies in the oven which may be easier for people living in cooler climates.


Freezing Chillies

Chillies handle being frozen very well too and are another very simple way of preserving or dealing with a glut. Simply bag them up and pop them into the freezer. They can be chopped up and thrown straight into your cooking - perhaps for a stir fry. Or they can be grated directly over a bowl of steaming pasta.

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