A really slow growth rate is a sign of stunted growth on your chili trees and you need to pray extra attention to them. Here are some factors that can result in stunted (dwarf) chili trees:
Lack of watering
Lack or excess fertilization
Too many weeds around the planting area
Soil pollution caused by waste from detergent or excess chemical fertilizer
Lack of harrowing
Macro and micro nutrients deficiency
Unsuitable pot size (usually too little)
Lack of sunlight exposure
Here are some things you can do as precautions and preventions to avoid having your chili trees stunted:
Do your watering on schedule; in the late afternoon and/or the morning. Make sure to water your chili trees as frequent and as much as your trees’ age needs because surely the amount of water they for seed germination and for blooming are different.
Use organic fertilizer (for example with chicken manure) for recently sowed chili seedlings or for recently moved chili trees to polybag for 20 days. After your chili trees have hit the 1 month old mark, you may use chemical fertilizer wisely and not too much.
Don’t forget to do some harrowing and weeding. Harrowing is important to keep your soil fine and loose to make it easier for your chili tree roots to absorb nutrients. Weeding is also important to get rid of unwanted wild plants that can steal nutrients from your chili trees. Use small hoes to do both of these things.
It is most recommended to plant your chili trees directly on the ground in open space instead of in polybag pots or sacks. Open spaces usually have better sunlight exposure.
Give your chili trees their needed organic and non-organic nutrients by giving them manure fertilizer with nitrogen, magnesium, and potassium. (reference)