The Pros and Cons of Where to Grow Chillies in the UK

We have tried it everywhere: chillies indoors… chillies outdoors… chillies in pots… in the ground… even a hanging basket. In the kids’ flower patch… on their bedroom windowsills… in a milk bottle… greenhouse… polytunnel… grow room. You name it, we’ve tried it…well, not on a spaceship but we hear chillies do very well up there!

During late Spring in the UK we all do the dance of the chilli plants: in and out of the greenhouse, attempting to harden off whilst not melting the plants in sub zero night temperatures. Location is key and conditions seem to change on an hourly basis. The forecast fluctuates between nights of minus two and days of 25 degrees.

Where’s a plant to go?!

So, exactly where are we growing our chillies?

No straight forward answer, sorry!

Each location has general pros and cons. In addition to those, each location also depends on unique factors to do with one’s own set up. For example: Greenhouses … is your greenhouse heated? Is it in full sun all day? Is it under a massive oak tree (see final photo)? Does it have a cat that likes to chew your plants, then sit on them? Will you be planting in the ground or in pots? Does the neighbour use pesticides right next to the door? All these variables ALSO need to be factored in when considering if a greenhouse is best for your chillies.

So, first let us consider what chilli plants prefer for optimum growth & yield in terms of:

  1. Light;
  2. Temperature;
  3. Humidity;
  4. Nutrition and pH;
  5. Support/protection/space;
  6. Pollination.

And then think of how to provide these at each general location. By no means definitive but here’s a visual to help compare…

At the Birdhouse, our outdoor growing season for chillies is limited to mid May to mid October. This is just not long enough for many of the chilli vareties we love to grow and so we extend by using lighter, warmer, safer places for our plants at either end of the season: namely the house early on and greenhouse & polytunnel in Autumn.

So here we go, this is how we do it…

Light:

In the house for Germination: We germinate in a transparent propagator. Light is not a required element for actual germination of chilli seeds – although one of our hacks to get tricky seeds to germinate is to fluctuate light exposure on the seeds. We place our propagator right next to a window. The emergent seedlings are then tight little plants, not the leggy beasts created by some in a darkened airing cupboard.

Birdhouse Seedling Headquarters is set up in a spare room of the house. Our light kit comprises two items: a low-tech south facing sunny windowsill and a high-tech full spectrum grow light. The great outdoors is just too darn dark to even consider in January.

Under Grow lights for seedlings: As soon as a seedling starts to show strong green cotyledon we move them to a paper pot under the a blue spectrum grow light for 16 hours a day. As they grow true leaves & eventually show roots from the bottom they progress to 9cm square pots under the grow light or on the windowsill. At this stage roatation is crucial as we only have one grow light and limited windowsill space. The plants will bend towards the sunlight so moving them around encourages them to bend the other way, strengthening their stems.

On the Windowsill for established seedlings: Space becomes limited as plants get bigger. Certain plants prefer to grow under the grow lights, Chinense types, especially. Others can cope on a sunny windowsill as long as they are turned to allow equal access to the light. In the UK the days are lengthening nicely in April.

Into the Greenhouse for growing plants: Once the plants are developing well they move to the greenhouse. Our greenhouse is next to a big oak tree but receives sun from 11am until sunset.

Young plants move up to the greenhouse. Protect leaves from direct sun as the raised UV light levels can damage them. Bubblewrap early on acts both as an insulator and light shade.
Paint-on shading can help protect leaves from scorching later on.

Spill out into the polytunnel to avoid overcrowding: the hardier types move out to the polytunnel when more space is needed. There are good light levels in there with the added bonus of built-in UV protection.

Planting outside: it is worth taking your time to harden the chillies off. This is for a number of reasons but, in terms of light, sunburn is an ugly thing that reduces photosynthesis. Just 10 mins in direct sun can scorch the leaves permanently. Make use of dappled shade, partially cloudy days or only put your plants in direct sun at the beginning or the end of the day. A week of this and they’ll be tough enough. Careful with the watering, droplets on leaves magnify the sun’s rays and will leave burnt patches.

Sunburned chilli leaf

Back into the Greenhouse for the last few pods: All outdoor light levels are subject to the time of year so that means that when Autumn approaches productivity drops off. We wait for the remaining fruit to ripen and then compost everything. No need for light there.

Temperature

Dans la Maison pour le Germination: Chillies like it hot. At germination stage we keep our seeds in a heated propagator between 25-36 degrees. This makes for pretty good germination rates. The propagator is heated at the base. We place our Chinense seeds down there and the others nearer the cooler top area.

Heated propagator keeps the germinating seeds at a constant high temperature

Tourjours dans la maison pour les Petit Babies: Seedlings are kept on heat mats in our grow room, under the warm grow light. This really boosts their growth and stops the external temperature fluctuations affecting them too much. At this stage constant temperature stresses them least. We water from the base with warm water. They stay in the house until space runs out: windowsills, dining table, anywhere that keeps them out of the icy blasts of a British Spring.

A la Serre: Then it is off to the heated greenhouse. Our chillies are kept warmer than our children (probably better fed too, ha!) We only move them out of the house if we can keep the greenhouse at a minimum of 10 degrees at night. On the odd night it gets colder we feel like very bad parents indeed.

A heater with a thermostat is your friend here. Ours is placed under the staging as direct hot air can cause the leaves to wilt and ultimately die off. Our greenhouse is set on a raised pad of concrete slabs. These store warmth during the day to release at night. Every little helps.

Bubblewrap, an electric heater and a warm stone floor all help keep the heat in and warm the plants at night

Et les plantes adultes: As a rule, at flowering and fruiting stage, we do not like our greenhouse to drop below 10 degrees at night or head above 35 degrees during the day. Flower drop, leaf wilt and less fruit setting is the result of temperatures outside of this range. A healthy difference between day and night temperatures is welcome though. Most chilli plants seem to do better with a bit of a break from high heat.

The more hardy chilli types…pubescens in our case, are sent off to the polytunnel as soon as outside night temperatures are hovering near to 10. We did this at the end of April in 2020.

Light a candle, place a terracotta pot on feet over the top. The terracotta absorbs and radiates the heat and keeps the temperature up far better than a naked flame. Safer too!

In May, there can sometimes be a cold snap, at a time when you least suspect it. Not great for an unheated polytunnel so we have a paraffin heater and candles under terracotta pots to keep the cold at bay. These strategies have meant that our brave San Pedro Rojos and Turbo Pubes have recently survived a week of zero nights in the tunnel. Huzzah!

Just look at the pubescens now

As Summer approaches, our priority moves towards cooling down, not heating up. A fan, ventilation through doors and windows and some shading will be options then. We generally leave the door wide open all Summer long. It still gets steamy in there but the air flow is better. This is our first Summer witha polytunnel but we fully expect to just roll up both doors and leave them there!

A la fin: As the evenings cool off we shut the greenhouse and polytunnel doors and only open up again during sunny days. Just long enough to keep those last few plants going to harvest their final fruit. Any plants still fruiting outside can be brought back inside to ripen off the last pods.

Humidity

Initially in the house: When germinating our seeds we pay special attention to the humidity of their environment. We soak seeds to give them an initial hit of moisture. We lay them onto an almost dripping paper towel inside a plastic takeaway container – no expense spared here! And spray. We click down three of the four corners down. This keeps the moisture in and around the seed but gives a little air flow. We regularly spray as the water evaporates.

As the seedlings mature, they are placed into paper pots of warmed, damp soil. They are watered from the base and misted if need be. The grow light and fan can be drying so we have spray bottles at the ready. Seedlings can rapidly deteriorate when dehydrated and many never recover. Keep it moist!

Chinense varieties do like humidity a little higher whereas the other are fine at moderate levels. Indoors, a regular misting will allow you to tailor humidity to each plant.

Humidity for older plants: Once the plants are in the greenhouse and they are watered from the base and the humidity levels are high during the day. Perfect for the Chinenses. The polytunnel gets a real humidity hit early morning as that is when the sun is first on it. We open the doors up mid morning to get air flowing through. Better for the Baccatums.

Outdoors, the wind and the sun can really dry chilli plants out. A good drink in the morning will help plants stay hydrated all day. Annuums will be fine in this environment. Pubescens have hairy leaves to collect their very own ‘cloud’ around their leaves. Humidity sorted.

Nutrition and pH.

At each stage of growth the nutrition levels need to be right for the plant. Growing in any sort of container means essential nutrients have to be added by you. They won’t appear magically.

In containers: Too much feed can be detrimental so don’t think more is better. Minerals can build up in soil and cause all sorts of trouble. Follow the instructions on the back of the bottle and make sure you give the plants plenty of water in between feeds. If in doubt, give less. Don’t forget to consider the existing nutritional value the soil you are using. Homemade compost and shop bought multipurpose can be surprisingly rich. Check the pH of your growing medium. An optimal range would be 6.0-6.8. Slightly acidic.

Open Ground: If you are planting out into your garden, or even into open beds within a greenhouse or polytunnel it is wise to prepare the ground with a basic feed first and then top up as is needed. We like to add Birdhouse compost to ‘feed’ the soil, a sprinkle of blood, fish and bone mix. And, this year, a banana compost, hopefully to support good strong, drought resistant plants. Our local soil is chalky, well above pH 7.0, often closer to 8.0. Far too alkaline for chillies really. This can be corrected with an addition of sulphur in early Spring. Then we use Chilli Focus weekly to keep those chillies focussed!

Soil will need to be revitalised if you plant in the same place each year. A thick top mulch and a sprinkle of Sulphur dust in the Autumn will mean beds are ready for action the following Spring.

Support/Protection/Space

Each chilli plant will need to be given enough space to be its best self. This is actually one of our (many) chilli failings. Too many plants, crowded in together. We’re trying really hard this year to pot up into the biggest pots possible – incrementally of course. A larger pot footprint then gives each plant more breathing room to do its own thing. Already the size and balance of the plants looks far healthier this year.

Some plants really do require support: stakes, frames, string, wires, whatever. There is nothing more heart breaking than a full branch of chillies being snapped off. A cane in the right place at the right time will help plants stand up strong. This is particularly important for chillies planted in the ground with little else around them.

And then protection…depending on where you have chosen your chillies’ final growing place, you may need to fend off unwanted visitors (strong sunshine initially, wind, birds, greenfly, slugs & snails, weeds, diseases, pets, frost and children) This is especially true when planting outside.

In a greenhouse the greenfly is omnipresent…ready to pop out thrips at an alarming rate. It is up to you how you choose to deal with them. We are squishers here. Ladybird farmers too. And later in the season, we encourage as many hoverflies as possible. And if all that fails, a night or two out in the open for an infected plant will generally clear the greenfly off and stop other plants being infected. Other folk try neem, Bug Off and soapy water. Up to you but be warned. You will have a greenfly in a greenhouse. Fact.

And eventually, back to the original question of where we grow our chillies?

Given the UK climate, growing undercover gives an extended season. Warm and light seems just right. We like to grow in pots as Birdhouse soil is be predominantly chalk, with an extra sprinkle of flint. For more infomation about our potting soil mix check out our previous blog post:

The Quest to Find the Best Soil

Here is where we will be growing our chillies at the Birdhouse this year:

The Birdhouse growing space

Where will you grow yours?

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