Grower Tip of the Day: Don’t put your chilli plants outside yet.
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This week we had two different customers contact us concerned that their chilli plants were wilting. They sent us pictures and it turned out they had put their plants outside.

Chillies are tender perennials

Important: Don’t put your chilli plants outside ‘yet’.

Capsicums are tender perennials and chillies are certainly “tender”. The absolute minimum growing temperature for mature and hardened chilli plants is 7 degrees Centigrade (46 Fahrenheit). Seedlings and small plants are much more vulnerable to lower temperatures and should be kept at a minimum of 15C.

As I write this it is 8C outside at 1:30pm and I can see the night time temperature will dip down to as low as 2C this week. This is way too cold for a small chilli plant. For now you should grow your plants indoors on your windowsills, in a conservatory, in a sunny enclosed porch, or a heated greenhouse.

And it is not just about ‘minimum’ temperature but also the range of temperature. Big variations in temperature over 24 hours can shock chilli plants. The result of this shock is a decrease in growth rate while the plant recovers from the shock. The end result of big temperature shifts is ultimately smaller plants and less chillies. This is why greenhouse thermometers track both high and low temperatures.

A good rule of thumb here in the UK is wait until the chance of frost has passed before you move your plants outside. For our part of central and eastern England we’re talking about (approximately) the first week of May.

Harden off your plants

Also, before you move your plants outdoors you will want to harden them off. Hardening is all about conditioning the plants for their new environment. For example, you should move the plant from a heated greenhouse to an unheated greenhouse or cold frame. After a week move the plant outdoors during the day but bring it indoors at night. The following week, if conditions are favourable, you can try leaving the plant outdoors overnight. If you don’t have these sort of facilities then move the plants against a sunny south facing brick wall and cover with a double layer of horticultural fleece. For the first week bring the plants in at night. After one week reduce the fleece to a single layer and, if conditions are favourable, leave the plants outside overnight.

I’ve only talked about the affects of temperature on your chillies but achieving the optimum growing conditions will also require monitoring and influencing other conditions such as humidity, light levels, and air movement (to name a few). If you want to know more about how to grow chillies like a pro consider coming on the Chilli Growers Workshop right here at the Chilli Ranch. And, always, Keep It Hot.

Dorset Naga chilli plant left outside overnight in March 2020.

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