You’ve decided to try your hand at growing the famous Serrano pepper. After plenty of time, investment, and maybe sweat, you finally get to try your first pepper off the plant. You take your first bite, and it has little to no spice! Why does your Serrano pepper pack no heat? Here are three reasons why your Serrano peppers aren’t as spicy as you expected them to be.
If your Serrano peppers aren’t spicy, pay attention to your pepper plant’s genetics (including possible cross-pollination if starting from saved seed), growing conditions, and nutrition.
1. Your Serrano Peppers Don’t Have the Right Genetics
Knowing the origin of your Serrano pepper can help you figure out how spicy it will be. Seeds from Serrano peppers with low levels of capsaicin will probably produce less spicy fruits.
The most important factor for determining the possible spice level of a Serrano pepper is its genetics. Chili peppers themselves are a genetically diverse plant group, with varying levels of capsaicin production, with spicier varieties containing higher levels of capsaicin. Studies show that wild pepper plants with higher levels of capsaicin are better protected against mammals, insects, and fungi that might destroy their seeds in wet habitats. Those plants are more likely to survive and pass on their seeds which will lead to additional spicy pepper plants. The spiciness of wild and domestic chilis depends on an interplay of genetics and environment.
So, what can you do to ensure you purchase seeds with the best genetics for the spiciest Serrano peppers?
To find spicier Serrano pepper seeds that lead to spicier fruit, don’t be afraid to shop around. Some crop breeders select for traits that make the Serrano peppers produce more capsaicin, though that heat is still a spectrum depending on both type and individual fruit.
Spicier types of Serrano peppers to propagate include Space Serrano, Serrano Fire, and Serrano Tampiqueño.
Alternatively, you can save the seeds of a particularly spicy Serrano pepper you bought at a market or grew yourself!
2. Low Spice Levels are Influenced by Growing Conditions
The genetics of Serrano peppers are important because they give you a range for how spicy the peppers can be. Whether or not that pepper becomes spicy tends to depend on the growing conditions of your pepper plants. If your Serrano peppers aren’t as spicy as you like, try monitoring and fixing the temperature and the watering frequency.
Serrano Peppers are Sensitive to Temperature
The healthier a pepper plant, the healthier and spicier its fruits will be, so you need to ensure your Serrano pepper is growing in the right environment. This means ensuring it is growing at the right temperature and that you are not over- or under-watering it.
If the environment is too cold for the peppers, this will mess with the plant’s ability to grow and produce capsaicin in their fruit. If you grow Serrano peppers outside, make sure the temperature doesn’t dip too far below 60° Fahrenheit (15° Celsius) at night or go much higher than 85° Fahrenheit (29° Celsius) during the day. Accidentally planted too early? Cover your plants with floating row covers, or bring your plants indoors if you’re able to, to protect them from the cold.
You’ll also want to make sure the type of Serrano pepper you’re growing is appropriate for your USDA plant hardiness zone. A pepper that does fine in zone 9 may not survive further north in zone 6!
For Serrano pepper enthusiasts who don’t live in warm climates, you still have options. The best one is to grow Serrano peppers in a greenhouse or other indoor space where you can control the temperature. Insulating or heat producing tools like black plastic mulch for ground growing plants or artificial lights and heat pads for potted Serrano plants can also help offset cooler environmental temperatures.
When to Water Your Serrano Plant
But how much should you water Serrano pepper plants? This depends on the growing stage of the plant. Before fruit starts to set, make sure to water your pepper plants regularly. After fruit begins to appear on the plant, a little bit of water stress–watering the plant less often–actually increases the amount of capsaicin in the plant.
Too much water can lead to milder Serrano peppers. We personally wait until the first inch or so of the soil in our potted pepper plants is dry before watering them. Don’t reduce the water while the plant is still flowering because a lack of water will cause blossom drop!
For more on how and when to water your pepper plant, check out our post How Often Should You Water Pepper Plants?
3. Lack of Nitrogen Can Lead to Low Capsaicin Production
Plants, like humans, do best when they get optimal nutrition. So, what kind of nutrients are responsible for capsaicin-packed, spicy pepper pods?
The most important nutrient for spicy Serrano peppers is nitrogen. Nitrogen is a key ingredient in the production of capsaicin and researchers have experimented to see how nitrogen levels affect the spiciness of peppers. The consensus is that high levels of nitrogen fertilizer result in both higher yields and spicier peppers.
But it is important to know when and how much nitrogen to give your plants, as too much nitrogen at the flowering stage could lead to a healthy plant, but a low pepper yield. Try adding nitrogen-rich fertilizer at the beginning of growth—after transplanting seedlings but before the Serrano pepper plant flowers or starts to set fruit. You must reduce the levels of nitrogen at this stage because if you keep giving the plant nitrogen fertilizer it will focus on growing foliage instead of putting its energy in to fruit production.
Some gardeners claim nitrogen stress (reduced nitrogen) at a later stage leads to fewer but more pungent peppers. But, if you’re looking to get a big yield, you’ll have to be careful about the amount of nitrogen you give your plants, as well as how often you do it.
In our experience, for best results, use a fertilizer high in nitrogen at the early growth stages, then switch to a fertilizer with lower levels of nitrogen when the plant begins to flower.
Common Myth: Cross-pollinating Peppers Affect Their Heat Levels (Not True!)
There are Serrano pepper aficionados who claim that growing mild peppers near hot ones will reduce the exalted pungency of the Serrano fruit.
This is distinctly not true.
Most hot pepper plants, including the Serrano, are self-pollinating. They have both male and female parts within their flowers and therefore don’t need their pollen to be carried by wind or insects.
Occasionally cross-pollination between pepper varieties does occur. If this happens, the spiciness of the fruit of the Serrano pepper plant will not be affected; it will retain all the characteristics of the mother plant. The seeds collected from these plants, however, may produce peppers with altered color or flavor.
This means that you can totally plant your Serrano peppers next to your favorite bell peppers and not compromise on their flavors! But if you save the seeds your next generation of pepper plants might be different from what you expect.
In the end, the heat of Serrano peppers comes down to three reasons: the genetics of the pepper you grow, occasionally influenced by cross-pollination; the growing conditions of the plant, such as air temperature and watering frequency; and the nutritional content of your fertilizer.
Each factor affects the spiciness of your Serrano peppers. If the environment is too cold, the plant is watered too frequently, or not fed enough nitrogen, your Serrano peppers will score lower on the Scoville scale.
Keep these factors in mind as you tend to your pepper plants, and you will have devilishly hot Serrano peppers just waiting to be picked.