Peppers want most of their nitrogen before flowering and most of their potassium after it. New Mexico State University puts a chile crop's season-long nitrogen use near 200 lb per acre. For a home bed, NMSU's garden guide calls for 1 lb of ammonium sulfate per 100 square feet before planting, then a 1.5 oz side-dress per 10 feet of row a week after bloom starts. Everything below hangs off a soil test, because the second most common feeding mistake is adding a nutrient the soil already holds.

What each macronutrient does

Nitrogen drives leaves and stems. Peppers need it early, and they punish a surplus later: the University of Minnesota Extension describes over-fertilized plants as bushy, leafy and slow to bear fruit. Phosphorus builds roots and supports flower initiation, and it moves through soil slowly, so growers work it in before planting rather than spraying it on. Potassium regulates water movement and cell wall strength and carries the load during pod fill. Calcium holds cell walls together. Magnesium sits at the center of the chlorophyll molecule, and a shortage shows as yellowing between the veins of older leaves. Sulfur feeds protein and enzyme synthesis.

What rate should I actually apply?

Field figures from NMSU. A chile crop uses roughly 200 lb of nitrogen per acre across the season. Growers band 120 lb of P2O5 per acre when soil tests below 10 ppm extractable phosphorus, and 50 to 80 lb when it tests 10 to 20 ppm. Nitrate-nitrogen holds near 30 ppm from planting through fruit fill.

Garden figures from the same program. Work in a half pound of superphosphate (0-36-0) and 1 lb of ammonium sulfate (21-0-0) per 100 square feet before transplanting. Side-dress 1.5 oz of ammonium sulfate per 10 feet of row one week after flowering begins. Our companion piece on dosing and diluting fertilizer converts those into container doses.

Fertilizer timing by growth phase

PhaseWeeksTarget NPK ratioNotes.
Germination0 to 2None, or 1-1-1 diluteThe seed carries its own reserves. Feed only once true leaves expand.
Early veg2 to 43-1-2 or 20-10-10Nitrogen-forward for leaf area and root mass.
Mid veg4 to 63-1-2 or 10-5-5Same ratio, larger volume as the plant grows.
Pre-flower6 to 82-1-2 or 5-10-10Nitrogen comes down. Buds appear.
Flowering8+1-2-2 or 3-12-6Keep nitrogen low. A surplus here costs you fruit set.
Fruiting10+2-4-8 or 4-6-10 with calcium and magnesiumPotassium peaks. Water evenly so calcium reaches the fruit.

Indoor container schedule

For coco and perlite or another inert medium, this is the program this site runs. It is a convention, not an extension recommendation, so adjust it to your water and your medium.

  • Weeks 0 to 2: plain water or a very dilute complete feed.
  • Weeks 2 to 5: 20-10-20 with a calcium and magnesium supplement every 7 days.
  • Weeks 6 to 8: switch to a bloom ratio near 3-12-6.
  • Weeks 9 and on: a potassium-heavy feed near 2-4-8 plus calcium nitrate every 5 to 7 days.
  • Leach the pots with clean water every 3 weeks to clear accumulated salts.

Outdoor soil schedule

  • Pre-plant: compost worked into the bed, plus phosphorus at the rate your soil test calls for.
  • Week 2: a balanced feed such as 10-10-10, watered in.
  • Weeks 3 to 6: 5-5-5 or 10-5-5 every two weeks.
  • One week after bloom starts: side-dress nitrogen, following the NMSU rate above.
  • Weeks 7 and on: shift to 4-6-10 or a tomato formula with added potassium sulfate, monthly.
  • Top-dress worm castings monthly and mulch to hold soil moisture steady.

The old version of this guide told you to drop a teaspoon of Epsom salts into every planting hole. That line is gone, and the next section explains why.

Does Epsom salt help pepper plants?

Only if a soil test shows a magnesium shortage. University of Minnesota Extension is blunt about it: without a confirmed deficiency there is no reason to add Epsom salts, and doing so can harm soil, plants and water. Worse for pepper growers, too much magnesium blocks calcium uptake, which makes blossom end rot more likely rather than less. Minnesota notes that magnesium deficiency turns up mainly on sandy, low-pH soils. Test first, then treat.

Does adding calcium stop blossom end rot?

Usually not, because the soil rarely lacks calcium. UGA Extension describes blossom end rot as a localized calcium shortage inside the fruit early in its development, and calcium reaches the fruit by riding the water stream. A dry spell followed by heavy rain, a waterlogged root zone, cold soil, or root damage all interrupt that stream while the soil test still reads fine. High ammonium, potassium or magnesium in the root zone competes with calcium and makes it worse. The fix lives in the watering guide, not the fertilizer shelf.

Micronutrients, and the boron trap

Iron chlorosis shows on new growth and usually reflects pH, not a missing element. Boron supports flower set and fruit development, and it carries the narrowest gap between deficiency and toxicity of any fertilizer nutrient. Toxicity shows as yellow and dead patches on leaf margins and stunted roots. Do not mix a borax solution by eye. Get a soil test, then follow the rate it supports. Zinc, manganese, copper and molybdenum rarely run short in a living soil. Our page on micronutrients for pepper plants works through the symptoms one at a time.

Soil pH, with a caveat

Most guides put peppers at 6.0 to 6.8, the band where the widest set of nutrients stays available. NMSU grows commercial chile in New Mexico soils at pH 7.0 to 8.5 and reports good crops, which tells you the plant tolerates alkaline ground better than the standard number suggests. Chase pH only when symptoms persist through feeding. See nutrient lockout in peppers and testing your soil for the procedure, and the diagnosis chart to match a symptom to a cause before you buy anything.

Products growers reach for

  • Base nutrients: Jack's 20-10-20, Dyna-Gro Foliage Pro, FoxFarm Grow Big and Tiger Bloom.
  • Calcium and magnesium: bagged CalMag blends, dolomite lime for soil, calcium nitrate for hydroponics.
  • Micronutrient blends: CSM+B, Micropak, Earth Juice MicroBlast.
  • Organic options: Down to Earth 4-4-4, Espoma Tomato-tone, Neptune's Harvest fish and seaweed.
  • Slow release: Osmocote Plus, Jobe's Organic Tomato Spikes.

Nothing on that list outperforms a soil test and even watering. Growers running C. chinense in containers see the difference sooner than anyone, because a 5 gallon pot leaves no buffer for a mistake.

Sources & Further Reading