NPK values for chilli plants

We humans are fussy eaters. Chillies are not. Chillies will take whatever meal you throw at them and, feast-or-famine, they will still grow, flower and fruit. Mostly.

However, the subtle science of feeding chilli plants well is a true art form that takes many a Summer to perfect. The variations of an ever-changing, seasonal menu for your chilli babies are as endless as Annabel Karmel recipes for troublesome toddlers. A good diet will hopefully produce a bounty of flavoursome, aromatic & glorious chillies to make your friends go oooh and ahhh. Much the same effect as when your young child selects an olive instead of a chicken nugget in front of an audience of NCT peers.

What does a chilli like to eat?

Let’s stick with the core ingredients for now: NPK, or Nitrogen, Phosphorus and Potassium to the uninitiated. Pretty much all feeds, fertilisers, composts, sprays, granules, enhancers, hydroponic potions contain these wonder components. As do most soils around the world. These macronutrients are the backbone of a good chilli plant diet. The most basic of fertilisers will provide an NPK ratio on its label. But just what are they and what do they do?

Nitrogen (N)

Why is Nitrogen necessary?

Think healthy leaves.

It is a key component of chlorophyll, the green stuff in plant cells. Chlorophyll uses sunlight to convert water and carbon dioxide into sugars as plant energy. Nitrogen is also a major component of protoplasm, the sappy contents of plants cells. Protoplasm is the vessel which holds trace minerals throughout the plant.

What does the correct supply of Nitrogen do to your plants? Healthy, green, lush plants. Strong stems and perky leaves. Speedy new shoots and flower bud formation.

What does the wrong balance of Nitrogen do to your plants? Too much Nitrogen will cause rapid growth, causing the plant to over commit. High Nitrogen feeds will inhibit flowering. Not enough Nitrogen and growth will be slow and the plant will end up stunted.

Traditional growers will add Nitrogen to their plants through blood meal, composted manure, composted coffee grounds. Blood meal is high in Nitrogen (12%).

Phosphorus (P)

Why is Phosphorus necessary?

It’s all about those roots and fruits baby!

Phosphorus is essential for plant cell division and development of new tissue. Think about when your chilli seedling is just getting going. All those new leaves, all that stem and root to grow, maintain and look after. Phosphorus is the ultimate support partner. It is in charge of seed development and as a result, timely flower formation, good sized and uniform fruit development and maturity.

What does the correct supply of Phosphorus do to your plants? Get the phosphorus levels right and you can expect strong early growth; plants reaching maturity earlier and roots showing through the bottom of the pot quickly. When potting on the first time, a good root system will be visible. It can also stimulate tillering, shoots springing from the bottom of the original stalk. making bushier plants.

What does the wrong balance of Phosphorus do to your plants? An excess of phosphorus in chilli plants can cause leaf issues, ending in leaf death. Too little Phosphorus and the plants may just not mature. In a few more detailed trials, it seems that less capsaicin and less fructose was found in plants that grew and fruited with lower levels of phosphorus. Not what is intended at all!

Bonemeal is high in Phosphorus (18%). Hoof and Horn is even higher (29%) Phospohrus is tricky to uptake, especially at low temperatures, low pH or in conditions with excessive iron in the soil.

Potassium (K)

Why is Potassium necessary?

Hearty growth and protection is the name of Potassium’s game.

Potassium regulates the closing and opening of stomata, and so can affect the amount of CO2 supply to the plant. CO2 is essential for photosynthesis and energy production. Low Potassium=low energy. Potassium plays a major role in the regulation of water movement within plants, in the roots and again the stomata. Essential transportation of nutrients, water and other minerals are also dependent on Potassium. Potassium is also a major player in cell wall thickening. This means that stems are stronger and all cells are less susceptible to disease.

Potassium has been proven to increase the likelihood of fruit setting in chillies. Not more flowers but definitely more fruit set.

What does the correct supply of Potassium do to your plants? Generally healthy plants with good tolerance to changes in environmental factors. Good drought and cold resistance in chillies. Allows fruit to develop and set well.

What does the wrong balance of Potassium do to your plants? A sad, stunted, yellowing plant will be on your hands if it is lacking in Potassium. More susceptible to drought, cold, pests as it will have thin cell walls. Less likely to grow quickly with strong stems. Waste products are not removed well, with yellowing of the leaves, ultimately ending in leaf drop. When seedlings first emerge they are vulnerable to damping off. Correct potassium levels at this stage can mean more seedings survive.

Potassium is linked to many growth enzymes in plants. Get the balance wrong and growth can be stunted. Too much Potassium may inhibit uptake of Nitrogen and Phosphorus as well.

Seaweed is a traditional plant treatment containing high Potassium. As is a more modern banana tea.

Is that it? Get the NPK value right and the chillies will be perfect?

Well, yes. And, no. Getting the NPK values balanced correctly for the plant’s needs at key points in the growing season is a huge, important task. BUT there are other factors too though. Other macronutrients (Sulphur, Magnesium and Calcium), micronutrients (Iron, Boron, Chlorine, Manganese, Zinc, Copper, Molybdenum and Nickel), micro-organisms, micro rhizomes, humidity, pH, pests, light levels, leaf quantity and size, pests, electronic conductivity of water, air flow and music choice.

The factors are myriad. Plenty more Googling to be done.

Homegrown Jalapeno chillies, the first of the season
Homegrown jalapeƱos, the first of the season

The science of feeding your chillies is in your hands. Maybe that weekly slosh of tomato feed needs rethinking?