Growing Hot Peppers – What Makes Them Hotter?

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Robert Pavlis

You are trying to grow hot peppers and you find they just don’t have enough heat. What are you doing wrong? What can you do different to grow really hot peppers?

People who love the heat from hot peppers are almost religious about making them hotter and hotter and this has resulted in a lot of online suggestions – many of them are just myths but some actually work. It’s time to separate fact from fiction and check the science to see what makes a pepper hot, and what can be done in the garden to make them hotter.

Growing Hot Peppers - What Makes Them Hotter?
Growing Hot Peppers – What Makes Them Hotter? photo source: Mad Dog 257

What Makes a Pepper Hot?

We are talking about the flavor here and not their sexy look.

The hotness in peppers is due to a group of chemicals called capsaicinoids and the most important of these is capsaicin, pronounced “cap-SAY-sin”. “The effect of the capsaicin has been described as delivering rapid bites to the back of the palate or a slow burn on the tongue and mid palate.” Capsaicin has no flavor or odor but acts directly on the pain receptors.

The largest amount of capsaicin is found in the white pith tissue that surrounds the seeds. The outer fleshy part of the fruit has significantly less and contrary to popular belief, there is almost none in the seeds.

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The venom of some tarantula species and capsaicin activate the same chemical pathway of pain and both have been used in research to study pain.

If you want heat in your peppers, you need more capsaicin.

The Pepper Heat Scale

Carolina Reaper, photo source: Dale Thurber
Carolina Reaper, photo source: Dale Thurber

How hot is hot? Scientists have developed a heat scale called the Scoville scale which measure the amount of capsaicin in SHU (Scoville Heat Units).

Sweet pepper: <100 SHU

Jalapenos: 2,500-8,000 SHU

Tabasco: 30,000 – 60,000 SHU

Spicy habaneros: 100,000-580,000 SHU

Ghost: >1,000,000 SHU

Carolina Reaper: 1.5 – 2.2 million SHU

Can You Tell Heat by Looking at Peppers?

Someone on our Facebook group told us that a family elder could identify the hottest peppers just by looking at them; ” milder, sweeter papers grow downwards, while hot ones grow towards the sun.” Is this true or a myth?

Members of the group quickly pointed to exceptions to this rule, including, “most ghost and habanero point downwards like bell peppers.”

Common Suggestions for Growing Hot Peppers

The internet provides a variety of suggestions for growing hotter peppers, including the following list. Most claims use some form of stress on the plants.

  • Choose a hot variety
  • Location on the plant
  • Reduce watering
  • Keep nitrogen levels low
  • Add sulfur to the planting hole
  • Avoid cross pollination
  • Let them age on the vine
  • Feed less
  • Epsom salt

Let’s have a look at each of these to see what science says.

Choose a Hot Variety

There are many types of peppers and some are certainly hotter than others. Select ones that meet your needs.

This link features the Worlds 10 hottest peppers. I don’t know how accurate the list is, but they certainly list some super hot ones.

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Location of the Plant

Research has shown that fruit from the second node is hotter than fruit picked from other nodes.

Reduce Watering

One common tip is to reduce watering so that the plants are stressed. This is normally done just after fruit set and some suggest giving plants a drink only when the leaves start to droop.

UC Cooperative Extension has been testing ways to make jalapeños hotter. Research in hot climates like Mexico, Spain and Thailand have shown that water stress can increase hotness, but testing in California showed that water stress made them milder.

Other researchers have found significant increases in capsaicin due to water stress.

Watering peppers less may produce hotter peppers but these plants are sensitive to water levels. Water stress should not happen until after fruit set to ensure the flower is properly pollinated and fruit starts growing. Waiting until leaves droop is probably too extreme.

Keep Nitrogen Levels Low – Feed Less

Most of these claims are very vague and say things like, “fertilize less than normal.” How does that help? You might already be under fertilizing.

One site said,”Nitrogen makes plants grow big at the expense of the fruit” and then goes on to suggest, “use a slower and gentler type of fertilizer such as rotted manure or compost.” Side dressing with rotten manure is not going to keep nitrogen levels low!

Good thing we have science.

Habanero pepper
Habanero pepper

Habanero peppers grown at various nitrogen levels showed the highest capsaicin level at very low nitrogen and at high nitrogen. The low end represented a stress condition. The high nitrogen level produced hot peppers as well as increased flowering and fruiting. High nitrogen gives you both hotness and high yield. Varying potassium levels had no effect.

Similar tests on jalapeno peppers showed a steady increase in capsaicin as the nitrogen level increased. Fertilizer stress did not increase hotness. This study, as well as the one above were done using containers in a greenhouse.

Padrón pepper plants produced hotter fruit with higher fertilizer levels.

There seem to be few field studies that would translate directly to a garden, but the science indicates stressing plants with low nitrogen is not the best way to grow hotter peppers. A home owner never knows how much nitrogen they have in soil, so it is difficult to manage nitrogen levels. All you can do is use a high nitrogen fertilizer and add extra to hot peppers.

Add Sulfur to the Planting Hole

It is believed that sulfur makes peppers hotter. The solution is simple. Put a strike anywhere match in the planting hole and the sulfur in the head of the match will make peppers hotter.

Sulfur does add an acrid flavor to things like onions, so maybe people associate this with being hot? Or they think a hot match will make peppers hot? Whatever the logic, it’s flawed.

The chemical formula for capsaicin is C18H27NO3. You will notice it does not contain sulfur, so it is unlikely that sulfur plays a significant role in the plants ability to make capsaicin. Besides the amount of sulfur in the head of a match is extremely small, it’s in the bottom of the planting hole, and plant roots will spread 4 feet in all directions. A match will have no effect.

All plants need some sulfur and if the soil is depleted, adding more will help the plant grow. Peppers like a slightly acidic soil with a pH of 6 to 6.8 and adding sulfur to alkaline soil can reduce the pH. However, there is no indication that sulfur makes peppers hotter.

Avoid Cross Pollination with Sweet Peppers

The logic goes like this. If you grow sweet and hot peppers together the sweet peppers can pollinate the hot peppers, resulting in fruit that is less hot. This seems very logical, but it’s wrong.

First of all, peppers are mostly self-pollinating which means a flower pollinates itself. It rarely uses pollen from another plant.

Secondly, even if the flower is cross pollinated, the fruit will have the characteristics of the mother plant, not those of the father plant. Any collected seed from a cross like this will have properties somewhere between the parents.

Cross pollination will never cause hot peppers to be less hot or more hot.

Should You Prune Pepper Seedlings?

It won’t affect the heat of the fruit, but pruning does affect when plants fruit and how they grow. Find out more in Should You Prune Pepper Seedlings?

Let Them Age on the Vine

The claim is that pepper fruit accumulates more capsaicin as it ages. The longer it is left on the vine, the hotter it gets. If you wait for those green jalapeños to turn red, you will have a much spicier pepper.

Testing of serrano peppers found no change in capsaicin during ripening of the green, yellow and red stages.

The two main capsaicinoids, including capsaicin, increased until day 40 (after fruit set) in cayenne peppers. This was followed by a sharp decrease and then a more gradual decrease until day 80.

Testing three types of hot peppers that are widely used in Mexico, found that capsaicin levels reached a peak at day 45-50, from fruit set, in habanero and de arbol and after 40 days in piquin. After that levels declined.

This research indicates that leaving peppers on the vine past 40-45 days (end of the growth period) will result in less heat. If you want super hot peppers, harvest them when the fruit stops growing in size.

Epsom Salt

I thought I had made it through the list without seeing Epsom salt, but no such luck. “Epsom salt delivers an immediate shot-in-the arm of magnesium to the plants and boosts growth.

There is no logic or scientific evidence that magnesium affects hotness.

What Makes Peppers Hotter?

The heat in peppers is dependent on many factors, including plant genetics, climate, geographic location and stage of ripeness. Warm weather regions generally produce hotter peppers than cooler areas. Warm nights, in particular, seem to be responsible for the higher capsaicin content.

Wild populations of peppers get hotter when attacked by insects and a fusarium fungus. They respond by producing more capsaicinoids which slows down microbial growth, protecting the seeds. Maybe a few insect chew marks on your peppers will heat them up?

Short of moving to a warmer climate, what can you do in your garden to make them hotter?

  • Water less once fruit has formed.
  • Fertilize more, especially with nitrogen. Even if the peppers don’t get hotter, you should get a higher yield.
  • Harvest 40-50 days after fruit set, or when the pepper stops growing in size.
  • Don’t listen to nonsense on the internet.
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Robert Pavlis

I have been gardening my whole life and have a science background. Besides writing and speaking about gardening, I own and operate a 6 acre private garden called Aspen Grove Gardens which now has over 3,000 perennials, grasses, shrubs and trees. Yes--I am a plantaholic!

14 thoughts on “Growing Hot Peppers – What Makes Them Hotter?”

  1. Hi, my question is for the reverse to hotness. I grow Trinidad pimento peppers, which is for cooking local dishes. They are flavorful but without any heat. The smell from cutting the peppers is like super hot peppers. If I grow them next to my Carolina reapers, will they end up with lots of heat? So in this scenario will cross pollination of heat with no heat result in heat in my pimentos?

    Reply
    • The current crop will not get hotter. Seed produced from non-hot peppers grown near hot ones could be hotter if they are cross pollinated.

      Reply
  2. So 2 different subjects Id like to pick your brain about. One about this article and one not lol

    I just found your site tonight while searching for a credible article for a pepper head friend that adding more phosphorus/potassium during fruiting stage will or will not help boost the plant to produce more flowering.

    At this point he has already had low flowering and I believe the low flowering is due from too much nitrogen in how he fertilizes.

    Maybe the P/K would balance out the nitrogen except someone told him to add a bloom booster and fish emulsion; which he did.

    So in my thinking no nitrogen should have been added; whereas he just double dosed the plant again with booster and fish lol

    I’d like to add that we are pepper growing addicts so to save room we grow basically in containers 5gal buckets down to 16oz cups.

    Anyways I’m still searching for that article, if you’ve written one let me know please

    Relating to this article you mention the research 40-45 days on vine to keep heat removing super hot pods when they are done growing to retain that peak heat.

    Hot peppers especially super hots the pods themselves will stop growing but then it can be another month plus for the pepper to fully mature and do all its beautiful color changes 🙂

    So many hots can take longer than the research states of 40-45 days to fully mature or does the research mean 40-45 after full maturity?

    I’m assuming maybe both depending on genetics of variety.
    The hottest pepper in the world Carolina Reaper can be such a drama queen and slow as a sloth to mature. haha

    Ok I lied 3 subjects…..Some of us Pepper Heads debate back and forth on the aspect of….does an immature hot pepper continues to mature off the vine, heat wise and/or to full color.

    What side of the debate would you be on for this?

    I imagine your extremely busy so even if you happen to read this; no need to answer all my ramblings. but if you know of think to the flowering issue I’d greatly appreciate it.

    I imagine I’ll be up all night reading your blog now that I’ve found it. This old gal is going to have to make some coffee lol

    Have a great one, be safe.

    Reply
    • “does the research mean 40-45 after full maturity” – check the link – it will explain how they measured it.

      high nitrogen can reduce flowering. Adding P and K does not neutralize the extra N. Bloom boosters do NOT work – that is a popular myth that just won’t die.

      Reply
  3. Hello Robert,
    I’m new to your website and love it! This is my 3rd year containter gardening with hot peppers. Last year was a bumper crop of really hot peppers, but constant problems with ants and aphids.This year, no heat at all in my Jalapeno nor serrano peppers, but no aphids either. Im trying different ideas from the internet, including, shocking and banana peel tea :-). It’s late July in central California and I was wondering if I should remove all the peppers from the plants and let them start again. As your article states, the peppers on the plants won’t be getting any hotter as time goes on.
    Thank you,
    Dale

    Reply
      • UPDATE: Late July, I harvested all the peppers and used them as sweet green peppers since there was NO heat. I stressed the plants by picking the fruit, cut the water in half and stopped fertilizing… lost half the foliage… then stared watering and fertilizing again with high nitrogen. The plants bounced back and I finally got some good heat in my Serrano and Jalapeno peppers with a second harvest in mid- October. So glad I didn’t give up and toss the plants. Thank you Robert for your information and website!

        Reply
  4. Over the years I have worked in Central America countries where the peppers were indeed hot. Numerous times I brought home the seeds and grew them in zone 5 . The fruit was not nearly as hot. So the variables you discuss Robert seem quite applicable. Thanks

    Reply
  5. Thank you for this information! I get so many question here (in a garden center) about what to do to increase heat in peppers. This is most helpful!

    Reply
  6. Hypothetically, if the chemical formula is “C18H27NO3”, then would it make sense to boost levels of these elements to increase the plant’s ability to bolster their capsaicin levels? The NO3 research seems to suggest this.

    The warm nights seem possible, but apparently they can grow very hot in arid climates like the dessert, which can significantly drop temperatures at night.

    It seems like a lot of variables to pin down! Much thanks for covering this topic! I appreciate the science, anything else is just a shot in the dark.

    Next year, I’m going to grow some extra high Scoville scoring varieties so hopefully they’ll be at least somewhat hot, despite my growing attempts producing the mildest results for the hot varieties I’ve tried.

    Reply
    • That seems logical, but it usually does not work that way. This compound, like all compounds is produced by a series of enzymes. What triggers the enzymes? What triggers the plant to make the enzymes? This is usually much more complex than people realize.

      Reply
  7. Interesting Robert
    I have been involved with growing and promoting chillies (as we call them here in Australia) for many years and, as you suggest there are many folk out there with their own special remedy. I can’t find the reference at the moment but I did read a paper some time ago which suggested that the real advantage that capsaicin gives to the plant is to protect the seed from fungal attack. This was based upon the location of the capsaicin within the fruit and its strong fungicidal properties. If that is the case then it’s likely that insect attack will result in increased capsaicin in response to a breach in the outer defences. I have tried pricking developing fruit with a pin and it does seem to work though I have not properly measured the effect. It is also likely that over, rather than under watering will also cause an increase because of the increased possibility of fungal development.

    Reply
    • My article mentions that insects and fusarium fungal infection can cause hotness – and gives a link.

      I believe it said the insects allow the fungus to infect the fruit, and that causes the production of capsaicin. Poking a hole would work provided the fungus infection takes place.

      Reply

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