Growing hot peppers – what makes them hotter?

By 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.

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,” according to Rosie Lerner of Purdue University. 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.

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 ghost pepper is so strong that protective gear is recommended when handling them.

The pepper heat scale

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

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

• 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.

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 by feeding 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 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 homeowner 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 four 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.

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 3 types of hot peppers that are widely used in Mexico, found that capsaicin levels reached a peak at day 45 to 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.

The ‘Carolina Reaper’ is considered the hottest pepper in the world according to Guinness World Records. Protective gear is recommended ifyou are handling ‘Carolina Reaper’ peppers.

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. Robert Pavlis lives in Southern Ontario, Zone 5, and has been gardening for over 45 years. He has published several gardening books; Soil Science for Gardeners, Building Natural Ponds and Garden Myths.

The ‘Carolina Reaper’ is considered the hottest pepper in the world according to Guinness World Records. Protective gear is recommended if you are handling ‘Carolina Reaper’ peppers.