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Hardiness zones explained: they are useful, but they only tell part of the story. Here’s why two growers in the same zone can get completely different results, and how to figure out whose advice actually applies to you.
Quick answer: A USDA hardiness zone only tells you the average coldest winter temperature. It says nothing about sunshine hours, summer heat, humidity or growing season length. Two places in the same zone can have wildly different growing conditions for chillies. Before you follow anyone’s growing advice, compare their sunshine hours, average temperatures and season length to yours. That one step will save you more failed seasons than any new fertiliser or gadget.
I’ve been growing chillies for around 20 years now and I’ll tell you something that might surprise you coming from someone who runs a YouTube channel about growing chillies: a huge amount of the growing advice on the internet, mine included, comes with a massive asterisk that nobody really talks about.
By the end of this article, you’ll know what that asterisk is and you’ll have a simple way to figure out whose advice actually applies to where you’re growing.
Prefer to watch the video? Click the link below:
Table of Contents
Where It All Started
I started growing chillies back in 2006. The Bhut Jolokia, the Ghost Pepper, was all over the news as the hottest chilli in the world. I wanted to grow it. But I also wanted the challenge of growing something in England that has no business growing in England.
The first attempt was brutal. But that struggle, that figuring things out, is why I started this channel. And here’s what I’ve noticed over the years, especially in the comments: people follow a grower, copy the schedule, the feeding, the timing and get completely different results. Sometimes worse, sometimes better. And they can’t figure out why.
The answer is almost always the same thing. Climate. Not skill, not effort, not which fertiliser you bought. Climate.
What Is a Hardiness Zone (And What It Doesn’t Tell You)
The USDA plant hardiness zone system was first published in 1960. It does one thing: it takes the coldest temperature recorded each winter over a 30 year period, averages those numbers and assigns a zone.
There are 13 zones. Zone 1 is the coldest, around −50°C. Zone 13 never drops below about 18°C. Each zone covers roughly 5.5°C, split into A and B subdivisions of about 2.5°C each.
That’s useful if you want to know whether a perennial can survive your winter. But that’s all it tells you. Nothing about sunshine. Nothing about summer temperatures. Nothing about humidity, rainfall, cloud cover or how long your growing season actually lasts.
Chillies are technically perennials. They can live for years in the right conditions. But most of us in temperate climates grow them as annuals, which means hardiness zones were never really designed for how we use them. They exist to tell you whether a plant can survive winter. That’s about it.
The problem is that people use their zone number as shorthand for their whole climate and that’s where it falls apart.
Same Zone, Completely Different World
When someone online says “I’m in Zone 8” and you think “me too, I’ll do what they do,” you might be making a big mistake.
I’m in Zone 8A. I share that exact same zone number with Dallas in Texas, Sacramento in California, and Canberra in Australia. Four places, same zone. Let’s see how they actually compare for growing chillies.
Zone 8A Growing Conditions Compared
| England (Shaun) | Dallas, TX | Canberra, AU | Sacramento, CA | |
| Sunshine (Apr–Aug) | ~900 hrs | ~1,450 hrs | ~1,350 hrs | ~2,000 hrs |
| Avg Temp (growing season) | ~13°C | ~26°C | ~18°C | ~21°C |
| Typical Summer High | 22–23°C | 36°C+ | 28°C | 38°C+ |
| Cloud Cover Impact | High | Low | Moderate | Very Low |
Sacramento gets more than double my sunshine hours during the months that matter. Dallas’s average growing temperature is double mine. Same zone number. Completely different reality for growing chillies.
Daylight Isn’t the Same as Sunshine
You might think England should have an advantage here. In June, I get over 16 hours of daylight. That’s longer than Sacramento. But daylight and sunshine are not the same thing.
What kills us in the UK is cloud cover. Sacramento’s skies are clear for most of the growing season, with over 90% sunshine in June and July. I can have 16 hours of daylight and 4 hours of actual sun hitting the plants. That’s the difference that matters when you’re growing something that evolved in warm, sunny climates.
What This Means for Your Growing
Think about what this means in practice. A grower in Sacramento gets three times the light and significantly more heat. If they tell you to start seeds in March and use a particular feeding ratio, that advice is built for their conditions. It works because they’ve got the sun and the warmth to back it up.
I start my seedlings in January because I have to. I grow in greenhouses because I have to. Without them, my season is too short, too cool and too inconsistent to get reliable results from most varieties. The greenhouses give me some control over temperature and protect the plants from wind and rain, but they’re not magic. I’m still working with the same limited sunlight.
A grower in a warmer climate can put their plants outside, in the ground and let nature do the work. I need infrastructure just to get close to what they get for free.
If you’re in a climate like mine and you follow that Sacramento grower’s March start date, you might run out of season before your superhots ripen. If you’re in Sacramento and you follow my January start date, your plants will be massive and rootbound before your outdoor season even begins.
Neither piece of advice is wrong. Both are right for where they were developed. The problem is when you apply one to the other without adjusting.
Why Some Growers Seem Fussier Than Others
I grow 400 to 500 plants across multiple greenhouses with automated watering and feeding. That scale, combined with a climate that doesn’t cooperate, is why I lean so hard on precision. I can’t hand water each plant and adjust on the fly. I can’t rely on a long, warm, sunny season to paper over mistakes.
If my timing is off by a few weeks, I lose a chunk of my harvest. If my feeding is sloppy, I see it in the plants almost immediately because there’s no surplus of light and heat compensating for the shortfall.
If you’ve got 10 or 20 plants on a patio or in a small greenhouse, especially in a warmer climate, you’ve got the luxury of flexibility. You can watch each plant individually, adjust as you go, be a bit rough with your ratios, and the conditions will forgive you. You don’t need my level of detail.
But understand that the difference between your situation and mine isn’t that one of us is doing it wrong. It’s that our climates demand different levels of precision.
That’s also why I lean on scientific research, peer reviewed studies and university extension work. I’m not running controlled trials in a lab. I’m one grower with one setup. But when your margin of error is this thin, you’d rather base decisions on published research than on guesswork. I need to understand why something works, not just that it worked once for someone somewhere.
Forgiving Climates Can Be Misleading
This is something worth thinking about when you’re watching growers online. Someone in a warm, sunny climate can use rough feeding ratios, start later, water approximately and still get impressive looking results. The climate does the heavy lifting.
That doesn’t mean their method is optimal. It means the conditions are forgiving enough that precision doesn’t matter as much. I’m not saying my climate is the hardest to grow in, either. A grower in the tropics dealing with humidity, disease pressure and pests I’ve never seen could make the same argument about their own challenges. Every difficult climate forces you to get precise about something.
In mine, it’s light, heat and timing. The point is that when conditions are tight, you find out quickly what actually matters and what doesn’t.
The 4 Things to Check Before You Follow Anyone’s Advice
Here’s what I’m asking you to do. Before you follow anyone’s advice (mine included, or any other YouTuber, or some person on a forum) look up four things about that grower:
1. Their location
2. Their annual sunshine hours
3. Their average growing season temperatures
4. Their growing season length
Compare those to yours. If they’re close, their advice probably transfers well. If they’re wildly different, you’ll need to adapt it.
A quick web search for “[your city] annual sunshine hours” and “[your city] average monthly temperature” will give you what you need in about two minutes. That tiny bit of homework will save you more heartache than any grow light or feeding schedule ever could.
Frequently Asked Questions
What hardiness zone do I need to grow chillies?
Chillies can be grown in almost any hardiness zone, but the approach changes dramatically. In colder zones (7 and below), you’ll likely need to start seeds indoors in January or February, use grow lights and grow in a greenhouse or polytunnel. In warmer zones (9+), you can often direct sow later in the season and grow outdoors with minimal protection. The zone alone won’t tell you how to grow. You need to factor in sunshine hours and summer temperatures too.
Can I grow chillies in the UK?
Absolutely. I’ve been doing it for around 20 years in Zone 8A. The key is understanding that the UK’s limited sunshine and cooler summers mean you need to start earlier (January for superhots, February for milder varieties), use greenhouses or polytunnels where possible and choose varieties that suit a shorter season. Jalapeños, cayennes and many annuum types do well. Superhots need more time and care, but they’re far from impossible.
When should I start chilli seeds?
This depends entirely on your growing conditions, which is the whole point of this article. In the UK or similar climates with limited sunshine and short summers, starting superhots in January and milder varieties in February gives you the best chance of ripe fruit before the season ends. In warmer, sunnier climates, you might not need to start until March or even April. Check your local sunshine hours and last frost date, then compare them to the grower whose schedule you’re following.
Why are my chilli plants not fruiting?
There are several possible reasons, but one of the most overlooked is that you might be following a growing schedule that doesn’t match your climate. If you started too late for your conditions, or you’re not providing enough supplemental light or heat, your plants might flower but not have enough energy or time to set fruit. Other common causes include poor pollination (especially indoors), over feeding with nitrogen, temperature stress, or inconsistent watering.
Do I need a greenhouse to grow chillies in the UK?
You don’t strictly need one, but it makes a significant difference. A greenhouse extends your effective growing season, protects plants from wind and rain and gives you warmer temperatures during those crucial summer months. Without one, stick to faster maturing varieties and give them the sunniest, most sheltered spot you’ve got. A south facing wall can work wonders.
Over to You
Drop a comment and tell us where you’re growing and what zone you’re in. I’d genuinely love to know what conditions you’re working with, because the more we understand each other’s climates, the better the advice we can share.
If you want to see the full video version of this, including the comparison data on screen, you can watch it over on YouTube. And if you’re just getting started with chillies, have a look at our beginner’s guide to growing chillies for a full walkthrough of what you’ll need.