If you are building the bed over existing soil. I would use 1 part sandy loam, 1 part compost , and one part peat moss. The black clay underneath will help drain the bed even though it is fairly tight. If the bed is over pavement or concrete then I would use a container mix, basically eliminating the soil and adding perlite instead. I would not use vermiculite because it breaks down fairly fast.

As far as fertilizer let the plants tell you. If the tomatoes and peppers are green and growing do not add fertilizer. If they look pale and stunted then add about a cup of balanced fertilizer such as 15-5-10 (3:1:2 ratio). I would probably add a cup to the mix starting out and mix it in. Most people over fertilize tomatoes.

By the way, it is getting late planting tomatoes. They do not set in temperatures over 95 degrees. Cherry tomatoes do better than larger tomatoes. Banana peppers and hot peppers do better than bell peppers in Texas.

I agree in part with the above :-) If this is a raised bed with a base that is open to the yo the ground or your indigenous/native soil, there is no need to get fancy. You are not worrying about the limited drainage and need for fast water movement that you would be with a real container.

So rather than a potting soil, you should be looking at a planting soil. These are intended to amend inground planting areas or to supplement garden soil rather than for container use and are perfectly satisfactory for a raised bed. Or just use regular garden soil, if you have it available to spare, amended with 15-25% compost.

Thank you both for responding. The bed in question is designed just like the one in the link--that is to say, it is basically a big, sub-irrigated pot, so wicking potential is key. Would the 5:1:1 mix work OK for this? I was not able to find pine fines yet, but I have seen shredded pine and cedar mulch that is not too chunky.

I just posted a very similar question after building a bed from the same video! Hoping we can both get our answers. I'm thinking of trying to locate some Pro-Mix to make it easier even if it may cost a bit more.

No, it has a bottom. The bottom is pond liner, which acts as the water reservoir. I went through the trouble so I could solve watering problems. It's not uncommon to have weeks of 100+ degree days here and the plants get very stressed by that, but my sub-irrigated five-gallon buckets I had last year worked very well, so I am scaling up.

What is OM?

For your purposes, I'd suggest something more like Raybo's 3-2-1 mix instead of Al's 5-1-1. Are you familiar with Ray Newstead's (aka Raybo) EarthTainer? If not, it's a self-watering planter built from plastic totes, and his potting mix recommendations should work just as well in your planter as they do in his. His general purpose mix is 5 parts ProMix BX (or Miracle Gro potting mix if ProMix is hard to find or too expensive) and 1 part perlite, but his preferred mix is 3 parts ProMix, 2 parts pine bark fines (aka "micro bark"), and 1 part perlite (or 3-2-2 if substituting Miracle Gro potting mix for the ProMix). Both will wick moisture well, but the latter will provide superior aeration. I don't know how the potting mix that you purchased compares to ProMix, so I'd err on the side of caution and liken it to Miracle Gro's potting mix.

I had heard of the EarthTainer in passing, but never fully read that PDF. Thanks.

Interesting that his results seem to have improved with the addition of more pine bark. Do you know if the pine bark absorbs water as well as something like a ProMix? If it did, that would suggest that the 5:1:1 would also work about the same, or better, than the 3:2:2, since it is primarily pine bark, as long as some additional nutrients/microbes were added.

I would assume that the improvements are due to the improved aeration that the pine bark fines provide -- the larger, irregularly sized particles create more air pockets than the fine particles that make up peat-heavy bagged mixes. On the other hand, pine bark fines don't wick water as well as peat, which is why the 3:2:1 mix is generally preferred over the 5:1:1 mix for sub-irrigated containers.

Thanks for the advice everyone. I finally got the bed in. I think it ended up more like a 3:1:2 mix based on the availability of ProMix HP and BX in my area. Most of it was HP, which has more perlite, so I didn't add any extra. The pine bark I was only able to procure in slightly smaller amounts. The consistency seems nice to me.

Michael- OM is Organic Matter. I don't know if that was answered or not. Pro Mix is just 2 parts Sphagnum Peat to 1 Part Perlite with optional Limestones added at about 3 1/2 oz per cuft. If you said you have a pond liner in the bottom, make sure to install overflow drains in the sides at the maximum height you wanted your artificial water table of aquafier. You don't want a swamp :-) Texas gets some rains. I do see some pipes in the photos. You can also built a PVC or other shade structure over the bed, to use when needed with burlap or shade cloth.

Addition: Mittlieder Method Gardeners also use raised beds on soil base with mixes ranging from Peat/Sand to Sawdust/ Sand.

Building a Wicking Bed