I found this super simple and cheap plan online a while back. I haven't used it yet as I'm trying 5 gal buckets this season, but it seems like it should be more than enough for a few plants. It should allow for ample root space, and it would be extremely cheap to build.

...if the height is worrisome, you could just do without the bottom liner. Kill the grass underneath with some cardboard. It would allow the roots to travel deeper if need be. For the weeds, a bit of mulch should do the trick.

Great topic. I will be watching intently. I was just wondering about these as my original intentions of growing 4-5 peppers this year on a first year growing are well out the window! I am already at 14 sprouted plants, more germinating and also on the way!

Yah, I wouldnt put a liner in the bottom. First of all, sixteen inches is pretty dang far for any plant to grow through even if we are talking weeds here...likely it is mostly just lawn grass though. Second, why stop the bugs from coming through? Most insects to include worms are very beneficial. The ones you usually have to worry about come from above.

I would go with the 3/4" plywood. I didn't even know they made 1" but if they do, it is probably extremely expensive. You could probably even get by with 5/8" or 1/2" if you wanted to shore it up with some 2X4's. Also, I suggest treated plywood and 4x4's. They don't use arsenic any more. They use more environmentally safe chemicals now. If you don't use treated lumber, it will fall apart in a few years. They also say you should break up the soil under the garden bed so the roots can penetrate if they get that far. I don't think you have to go far though. 4-6" should be plenty but I am not sure how deep the sprinkler system is. Skip breaking up the soil if you are concerned. And the last thing to consider is the soil. If you order it by the truck load, it isnt that expensive, but if you were thinking of buying it by the bag, you should sit down and do the math. You are talking about 45 cubic feet of dirt. At roughly 75 pounds per CF, you are looking at over 1.5 TONS of dirt. Yep, about 3300 pounds. That would be more than twice the load limit of a normal pickup truck. But your peppers will love you for it.

Raised beds normally do not have a restraining bottom. Some people do that when they built their beds on things like invasive grass. Or they lay down wire cloth. So then if the foundation has some half decent native soil with normal drainage even a 12' deep bed frame should do. That is exactly how I have done it.

FRAMING MATERIAL:

I would never use plywood. It will warp and rot. Even if you use marine plywood, it needs some treatment. Even 2" by 6" pine should be better than plywood. I have used 5/8" thick ( 6" x 6') cedar and fir. Stacking 2 of them you will get about 12". With 3 you will have 18".
That is about my 2 cents.

I've built a lot of raised beds for myself and other people. Use 2X12 treated lumber, or if you're flush use cedar. If you're worried about the chemicals in the treated, line it with black plastic stapled on the sides. Remove grass and trench 1" down for a little support. Use four 3" screws per joint. Make sure the screws are rated for ACQ treated lumber. Put one right-angle brace (Z-Max) on each top corner for additional strength attached with #9 TEK screws. Level it up too. Don't let the ACQ lumber set out in the sun without covering it or it'll warp very quickly. Build it then move it on site. This one is 10X4' with four Bhuts in it.
I build a LOT of 2X2 individual planters out of 5/4X6 decking material and ripped 2X4's. If anybody's interested, contact me and I'll send you the cut sheet and dims.

this is a pic of some of my raised beds. I would never use plywood, even outdoor plywood, just not weather resistant enough, seems like the chemicals they use for treating wood anymore just doesn't work well, at least not the stuff I've bought. I also have plastic down, but then I already had it down in the garden. I just got a load of compost yesterday to top them off.
Pam

8 - 12 inch should do fine, especially with an open bottom.

Josh

Thank you all for the advice.

I am going to leave it bottom-less. I think I will use 2x10 or 2x12's, No plywood. The sprinkler PVC is buried the length of the bed I want to make against the house wall and it is buried about 10" deep, so this way I do not think I will have to worry about the plant roots penetrating the PVC. There is grass currently in the area I want to do this in, but I will rough it up to loosen the top-soil. The wall that this will be against is a South facing wall and should be great as it gets plenty of afternoon Sun I am just worried because of the summer time 110 degree temps and 100% humidity here in Central Louisiana.

Again thank you all for the advice,

Bill

Thank you all for the advice.

I am going to leave it bottom-less. I think I will use 2x10 or 2x12's, No plywood. The sprinkler PVC is buried the length of the bed I want to make against the house wall and it is buried about 10" deep, so this way I do not think I will have to worry about the plant roots penetrating the PVC. There is grass currently in the area I want to do this in, but I will rough it up to loosen the top-soil. The wall that this will be against is a South facing wall and should be great as it gets plenty of afternoon Sun I am just worried because of the summer time 110 degree temps and 100% humidity here in Central Louisiana.

Again thank you all for the advice,

Bill

You may have to employ some shade cloth or something else during peak heat. However, Peppers seem to take the heat better when in the ground than in containers.
Bruce

Bill,
Consider using drip irrigation for the bed since you already have a sprinkler system installed. You can buy replacement heads for multiple 1/4" drip lines. Regular watering and mulching are a must in the hotter, dryer zones, IMHO...

Definitely, drip irrigation is a must. This spring I'll be spending my time fixing and replacing all of my drip irrigation that the puppies have destroyed in both my vege and flower gardens. ;-( The drip store has some of the best prices and biggest selection, that's the only place I purchase mine, I love their 1/4" soaker.
Pam

Bill....check out some of the raised bed and/or square foot/lasagna discussions out there for more info.

You don't really need to loosen up the grass. Thick layers of newspaper and/or cardboard will work just fine at choking out the grass.

Find a way to kill of the grass and do not till or anything deep. You want to keep your soil structure under your bed so your peppers can dig into the hard surface. Tilling ruins soil for the most part. Also I would look into making or buying some stump tea or anything that promotes micro organisms or just use some good ol compost in your bed.

perhaps the more experienced in ground growers can correct me if I'm wrong, but I've never heard of pepper roots messing with PVC lines. it's not an oak tree.

I say rip out the grass below, and if you're afraid to dig down for fear of breaking sprinkler lines, use a rake to loosen up the soil.

and I don't think it necessarily needs to be 4 ft wide, especially if it's going up against a wall so you can't access it from one side. you don't ever wanna have to walk on your raised beds to get to the ones in the back, or you'll compact your soil. 30" is about the limit of how far an average sized human can comfortably reach back.

Roots generally rupture PVC water lines by applying pressure to the pipe against a hard surface like a rock. The root will expand and force the pipe to snap or kink, which will cause a leak. I don't know of any root that can penetrate a good PVC joint with 60-100 PSI water pressure in it.
A 4' wide bed will give the roots more room to spread out to the drip line of the plant and absorb nutrients. Point drip is not as effective as a spray drip because it forces the roots to follow the water down, instead of spreading out.
Your mileage may differ depending on soil type...

hahaha, that's usually not an issue with me (I have soaker and point drip) cos I start watering when I get home from work 5-6pm , go inside and forget all about it. That is, until the next morning when I am taking a shower and wondering why I have no water pressure. ;-( by then the entire area is well flooded.
Pam