I have two different varieties of bell peppers I'm trying to grow in containers. One of my bell peppers, orange sun, is stuck in the seedling stage with only two leaves. It never developed its third leaf. My other bell pepper, California wonder, is bigger and definitely seems like it could get bigger, but it hasn't been growing as well as my tomato has. They are in 5 gallon containers, so I don't think the pot size is an issue. And I have also given them fertilizer.

I started growing them from seed late (early June) along with my tomato and zucchini, but my bell peppers aren't getting bigger while my tomato and zucchini are big and healthy. My tomato is about 3 feet tall, but the California Wonder is probably around 6 inches tall.

I've never grown bell peppers before, and I thought bell peppers were relatively easy to grow. What can I do to help them be as strong and healthy as my tomato and zucchini? Is it possible that the weather has been too hot (consistent 90+ degrees) and it's stressing them out from getting bigger?

Bell peppers are the most difficult pepper to grow but usually respond well to good conditions.
First realize that peppers in general are very SLOW starting. Tomatoes and zucchini are the hares to the peppers Tortoise.
Your containers should be adequate and peppers love heat so you should be fine in that area.
Peppers can be overwatered , so be careful on that front. Assuming you have a good growing mix you should be ok.

I agree with Dillard...bells are slow. I have gone to mid-season varieties since the long season bells don't begin putting out fruit until the possibility of frost is looming. I have stopped trying to get Cal Wonder to produce in my short pepper season. I get green but not ripened peppers. All my peppers get about a two week early start compared to tomato seeding. Mid-February seed starting as compared to first of March, and I am in 5B or 6A.

You say you have fertilized your peppers. Like tomatoes, nitrogen fertilizer will give lots of green plant but no fruit production. Use a "bloom buster" fertilizer (like 8-30-30, low N, higher P and K formula) which helps roots and fruit. In containers you need to replenish nutrients every ten days or so as watering flushes out nutrients. I add water soluble fertilizer to the water once per week. Mine are all in-ground so I do not fertilize unless the plants are under stress and need a shot.

Ahh, I didn't realize bell peppers were slow and difficult to grow. I'll just be patient with them then! Thanks for your responses!

RE: fertilizer. I used a 10-10-10 fertilizer, and since they're not big enough to start flowering yet and need more leaves, I think it might be fine.

agreed completely, peppers are soo slow, tomatoes are monsters. I started pepper seeds indoors in January for planting out late April to early May.

To add to what others are saying, yes peppers are slow. If you started seeds in June and already have 6" plants, I would say you are way ahead of the curve. I would not fertilize them anymore, you will risk a tall, leggy plant with lots of leaves, but no fruit.

I started my bells inside mid March and planted outside in the ground after mother's day. They were really slow to take off, even in the ground, but in June they finally started growing. My biggest is now over 3 feet tall and I've got peppers. They really seemed to need days in the 80s-90s, and nights above 70 as often as possible. My watering and fertilizing schedule is different from most since I have clay soil. They have been doing better since I started mulching as well (I use a thin layer of grass clippings). You can see my rows of peppers in the middle. There's bells, mini bells, and snack peppers mixed in there.