Jennie,

Some plants are taller than others, and it can vary quite a bit depending on what variety you planted. For jalapeno and bell pepper plants to be 12" tall now really isn't too bad as long as they are a healthy green color, don't look diseased and are blooming and setting fruit. They'll keep growing and producing all summer long and you should have plenty of peppers.

Do they have peppers on them? If so, they're putting a lot of energy into producing that first round of peppers, so they'd be growing a bit more slowly than peppers that haven't fruited yet.

Do you remember when you planted them? (Approximately?) If you set them out while the soil temperatures were below 55 degrees...and that likely would have been in late March(?) or maybe earliest April...that can cause them to stunt and stay small for months.

How about spacing? I put mine about 18" apart, and some folks prefer 24", but that seems kind of far apart to me. If they're too close to one another, they could stay smaller.

Are they in full sun, or if not in full sun all day long, are they getting 6 to 8 hours of direct sun daily? Some mid-day or afternoon shade is fine, but they still need 6 to 8 hours of sun to grow well.

Is your soil well-drained? Peppers need well-drained soil and will grow more slowly if they are in heavy soil that stays very wet for a long period of time.

I assume you have the proper soil pH for them. They'll grow well at a pH between 5.5 and 7.5.

Does the soil have a decent amount of humus or compost or other organic matter? Peppers need that. If they are in soil that is very, very sandy, they could be malnourised. If they're in sandy loam or improved clay, they should be fine. If they're in heavy clay, their roots may be struggling to grow well in that clay.

Did you start with transplants? If so, I wouldn't worry. If you direct-seeded them into the garden, of course they're behind others that started out as transplants because pepper transplants often are 8 weeks old (or older) by the time they go into the ground.

If the soil is lacking in nutrition, they may need to be fed.

If you're in a dry part of Oklahoma that is not receiving regular rainfall, they need to be watered deeply once a week...try to give them enough water to wet the soil -8" down beneath the surface. Infrequent deep watering is better than frequent shallow watering.

So, if they are truly lagging behind other local gardeners' peppers, and you don't believe it is a difference in the plant variety's natural size or a deficiency in rainfall/irrigation, then try to figure out if they were planted in soil that was too cold, slow-draining, or infertile. It's got to be one of those if all other things are equal.

Likely all they need is time and they'll catch up with the other ones you're comparing them to. If you remember the name of the variety you planted, we can look them up and see what their mature height is. I grow some bell peppers that top out at 18" and others that get to 3', so there's a lot of difference between different varieties.

Dawn