How and When to Plant Chili Seeds in the UK

It’s the hot fruit that sounds like it’s cold. Or at least that’s one way to think of chilli peppers. Spelled “chilli” in the UK and “chili” in the US, there are an estimated 3000 varieties in a myriad of colours, shapes, flavours and levels of heat. From the gentle warmth of a poblano to the fiery challenge of a ghost pepper, they cater to every palate and adventure level.

This immense diversity is great in the kitchen where they can just as easily add a smoky whisper to a barbeque sauce as zesty zing to a fresh salsa. They even make their way into chocolates and desserts. And let’s not forget that they’re packed with vitamins, antioxidants, and the mighty capsaicin.

The question is, how and when to plant chilli seeds in the UK. And that’s what we’re here to find out. Ready to turn up the heat? Let’s go.

Part of choosing how and when to plant chillies in the UK is understanding the varieties available. When thinking of chillies, one might picture the narrow tapered curve of the jalapeno, perhaps in red or green. In fact, they come in a staggering range of shapes, sizes and colours. Some resemble apples, tomatoes or cherries. Their plants might be no taller than eight inches while others reach the height of an average 7-year-old. Meanwhile they can appear in hues including green, yellow, orange, green, and black.

Flavour profiles can also differ markedly, from sweet and mild to violently hot. Chilli heat is measured in Scoville Heat Units or “SHU.” Anything from 3,000 SHU is considered hot. And they range from milder varieties such as banana peppers rated at 500 SHU, to the 2,500 to 8,000 SHU of jalapeno right up to the blazing heights of 2.693 million SHU, courtesy of the Pepper X variety.

Thought to originate in South America, it’s perhaps unsurprising that chillies prefer a much warmer environment than that found in the British Isles. The ideal temperature is around 21 degrees centigrade for seeds, between 16 and 18 degrees for seedlings and between 15 and 30 degrees for plants. They also require a sunny spot.

So, where does that leave the issue of how and when to grow chili seeds in the UK? For one thing, as well as starting from seed, chillies can be grown from young or grafted plants, offering a slightly more resilient option in the cooler climes of the UK. Beyond this, there are various ways to create the perfect conditions for growing chillies, from starting them off indoors to using propagators and greenhouses.

In terms of when to plant chili seeds in the UK to maximise the chilli growing season, it’s best to sow seeds indoors from late winter to mid-spring. This can be done on a warm windowsill or, for more consistent results, within a heated propagator. An interesting technique for gaining an early start is overwintering, where chilli plants are kept in a bright, heated area during the winter to be ready for the following growing season. Seedlings are then transplanted to individual modules or small pots once they reach about an inch tall, providing a robust start to their growth cycle.

Until at least late May, young chilli plants should be kept indoors where it’s warm. They’re then ready to move to their final growing location. As well as when to plant chillies outside in the UK, there’s also the question of location. Ideal sites include greenhouses and polytunnels. Conservatories are also an option, or a sunny indoor windowsill for compact varieties. When grown in containers, a 9-inch pot filled with peat-free multi-purpose compost is suitable for each plant. Alternatively, ground planting requires well-drained, fertile, and slightly acidic soil, with adequate spacing and protection from wind by covering with cloches until at least June.

We’ve seen that chilli plants thrive in warm, humid conditions, ideally within a temperature range between 15 and 30 degrees centigrade. Growing in a greenhouse offers some flexibility in the event that these conditions are breached, like ventilating in the case of hot weather or damping down when it gets too dry.

Regular soil moisture checks are crucial to prevent the plants from drying out, requiring a careful balance of watering and mulching to retain moisture. Once the plants reach a foot in height, pinching out the shoot tips can encourage more fruit growth, while larger plants may need support with canes.

Greenhouse-grown chillies are usually ready for harvest from mid-summer, whereas those planted outside mature by August. Chillies can be harvested while green for immediate or later use or allowed to ripen on the plant for enhanced heat and flavour. It’s worth noting that letting chillies ripen on the plant may reduce overall flower production. Once harvested, chillies can be dried or frozen for use throughout the winter.

Overall, from the initial steps of how to grow chili seeds in the UK, leveraging indoor environments and heated propagators, to the eventual planting of chillies outside in the UK during the warmer months, it’s clear that with a bit of care and planning, a spicy harvest is well within reach.