I would say heat and light are the two big things pepper plants love.

I put some pre-seeds into the a raised box 30 days ago, and they are 3x that size easily. I'm in an 8b flipping 7a though. Lots of light throughout the day, but cold temps at night now which is unheard of for this area.

These plants thrived during the hot days though. Some even started fruiting when too low to the ground.

If these aren't in direct sunlight for 6+ hours a day with 70F or better temps, they will be on the smaller side. Maybe consider getting a heat mat if they aren't ready for the outside environment yet.

They look decent enough, but if there was one thing I see that could be improved, perhaps, it's that people very often don't bother adding aeration to their soil. Like a third of perlite, even half depending on the plant. Just keeps the soil so much better draining so watering doesn't compact it and the plant has an easier time making roots.

I've just noticed it's the most limiting factor usually, and soils nowadays are all pretty shit. Even the supposed "cactus soil" I got was muddy as hell, definitely not good for cacti, I barely used it to plant my cannabis. It's for the mother plant, so it being a bit slow growing is fine.

But I have noticed the quality and aeriness of the soil impacts the early phases of growth quite a lot. After there's a proper root ball, less so.

Echoing what everyone else has said, peppers love heat. Ours were started about the same time as yours and they look about the same. They don't really start popping off until they are outside, with room to grow and it gets hot hot.

Good job getting them started so early, I'm sure you will be rewarded once their established root systems are given the environment they need to thrive in.

Quite slow. They can take their time at the beginning. But that's far too long. We've had some frigid days where I am so that doesn't help. If they start getting sun and heat like crazy they'll take off. If you're feeding them consider holding off. Just water for a bit.

Too cold.

You won't see much growth if nights are below 58–59F.

I don't plant chillis until a certain time of year and then I have about 18–22 week window to try harvest before temp is off again. I planted as early as possible last season and I thought some species weren't going to make it to harvest in time.

I used to live in a more tropic climate where peppers flourish fast all year round, so it's taken some getting used to and been disappointing.

My tip is to leave them outside permanently and cover them in 1-2 layers of frost cover fabric (no idea what it's called in english, it's thin and light and lets light through). Remove layers of fabric gradually while the plants acclimate.

This way you can keep them in full sun (they need lots of light now) without risk of burning them. Also you won't have to constantly carry them around.

It looks like you are growing those peppers and coco coir? They need to get fed more nitrogen and make sure the pH is between 5.8 - 6.0. of the water/fertilizer you are giving them.

:laughs in zone 11a:

Same here.