Have you considered using containers instead? Easier and eliminates all the soil problems.

Another option would be a slow drip irrigation set-up using 1/2 or 1 gallon per hour drippers. Set on an auto timer and you can provide a good consistent soil moisture level. How many plants are we talking about?

Another alternative - but less effective IMO - is the water absorbing granules mixed in with the soil. Moistearth is one brandname. Perhaps what you mean by "soil enhancer"?

The problem with your planned approach is it creates a pool. Water will always flow down, never back up and buried like that you have no way to monitor the water build up. It creates the same problems one finds using a container without drain holes in the bottom - root rot primarily.

This, if I understand correctly what your plan/need is. If not, feel free to ignore. :)

Dave

I'm going to respectfully disagree with Dave. I think
that your approach will work with an amendment, such
as Kellogg's AMEND, and will solve much of the problem.

I don't believe there will be any pooling in the holes due
to the decomposed granite nature of his soil. I have
caliche which is similar, but a bit more moisture retentive.
Water will drain quickly through the amendment and into
the local soil.

Not sure about the shallow pan part though. I'd put holes
in the sides of the thing so you would have a bit of a pool
to capture the water (maybe an inch above the bottom?).

I used to grow in containers here in SoCal and had saucers
below the pots. Most hot days, I'd fill those saucers which
were about 1 1/2 deep in the morning before leaving for
work and they'd be dry, dry, dry when I got home.

How about this? (I hope I understand the posts above.)

Make holes about one foot deep. Place a tray (maybe a cake pan) in the bottom of each hole. Fill the holes with soil and plant the seedlings.

The idea here is to trap some water under the plant at the one foot level. This is similar, I think, to the principle of the earth box. Some of the retained water will wick upward if the soil has enough organic material. Also, roots will seek out the water in the pans.

Yes, undrained pots will rot roots. But I don't think there would be root rot in this situation. After all, roots don't rot in a hydroponic set-up or in earth boxes.

Jim

DAVE: slow drip irrigation set-up using 1/2 or 1 gallon per hour
yes that is what i just set up,but havent completed yet.
That may be enough as you suggested.
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GAGUY: Dave had valid concerns that the holes in the pan may clog the drainage,but knowing my soil's massive perosity, i dont see that as a likely occurance. it could happen though,we're just sorta guessin here.
I think i may try different approaches on separate plants just to see.
Side holes is a good idea. Ill just have to pick somethin and do it,then Ill know for next time.
At first I dismissed you idea of raising the tomatoes in just pots. 1 because I have 5 plants. 2-not place to keep them without being a mess what with water dripping all over and tubing or pvc everywere.
3.im growing squash off the same line as the tomatoes. That seemed like too much work and a big mess.
Then i thought a bit and realized i could make basic barebones 2x4 shelves like I just did in my garage and attach them on the outside wall of my garage. There's plenty of space and its only dirt/sand around my garage so water dripping isnt an issue.
What I do need is to screen the plants in with 1/4 inch square mesh. That is easier and cheaper to do than doing that with a garden on the ground.
I have coyotes, chipmunks,squirrels,birds bugs that devour any and all fruit and plants that bear any fruit.Flower plants disappear too. I had gardens in the sacramento valley out on a small farm,and had just as many critters,(but they never even got close to being a problem to my garden.. Theyre like you'd imagine an invasion of locusts would do.
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JIM:
Your suggestion is what i tried to describe in my original post
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thanks for the input all.

If you decide to go with drip irrigation I have another suggestion for you to consider. It is something I implemented with some of my containers last year that I was having problems stabilizing moisture content in and it has worked well. No inground experience with it though.

I set up 2 separate lines to each plant. 1 line using 1 gallon drippers and 1 line using 1/2 gallon drippers. By combining and/or alternating lines used and times run I can get almost infinite control over the soil moisture levels.

Just something to consider.

Dave

"JIM:
Your suggestion is what i tried to describe in my original post "

I thought it might be. Good luck, whatever you do.

Jim

"Yes, undrained pots will rot roots. But I don't think there would be root rot in this situation. After all, roots don't rot in a hydroponic set-up or in earth boxes. "

The roots don't rot because ....they get Oxygen

Feel free to skip this but I recently moved from norcal down to SD area. We have many different types of dg. In my back yard I excavated about 1000 yards of dirty dg. My plan was to amend it, but as the soil weighs to much I'm thinking I'll only use about 10% sand in my soil mix. Right now current mix is 8 parts bulk soil, 1 part wood mulch, pearlite small and largge, azomite trace minerals, Coco coir. 1 part BBB ( blood bat and bone) then I let it sit for a month to homogenize. This soil has proven amazing for any soft leafed plant (tomatoes, melons, tomatoes, etc).

So now to your question. I have a couple ideas

1: I suggest you dig your hole asd you said 2 x 3. Then go buy clay dust, wet clay pellets, or bentonite. AI hold water and restrict flow. From my research the only way to get dg back to soil is to ad clay to coagulate the aggregates. This will also give you a large inert medium in between mulch and dg. Another option is to put about a foot of mulch on top of your soil add amendment as well as later in year you can till in for better soil makeup.

The last option is to put I water hold medium such as woody mulch or Pete, it Coco under dg.

It's extremely important to use slow drip irrigation with dg as it tends to erode an area with heavy watering.

Look up a water well. Roots will not rot as long as you use cold water as child water has ability to hold more oxygen. If your worried about that. Throw pearlite in at the bottom so there is always air down there.

Feel free to message me for more info

Veda

I would think you're a good candidate for planting your tomatoes next to ollas. Real clay ones, not one of those faux ollas made out of plastic milk jugs or whatever. Combined with some extensive soil amendment, that might do the trick.

I'm thinking of another water-holding soil amendment - Diatamaceous Earth. I have no clue about how it would work in your conditions, but others might.....

Linda

Our entire acreage is decomposed granite. We use an automatic drip system. Depending on what we are watering, we use 1/2 to 1 gallon emitters. They do get clogged, however, so we need to constantly check to make sure they are actually working.

On small scale you might add lots of peat moss and vermiculite.

And how about generous amounts of organic patter.

I don't know what "decomposed granite" means. That should be just some fine sand. Inorganic matter don't decompose.

Sey

Sey, decomposed granite is pretty much what sluffs off the huge granite boulders many of us in California have. It is full of minerals, and depending on where you are located, some regular dirt and organic matter too. It's NOT fine sand. It can hurt your bare feet to walk on it, but it's advantage is that it is very well drained. Good for some things, not so good for others. Any plants needing acid soil won't find it too friendly. Alkaline lovers are fine with it. It can be found in many climate zones here in California.

Wish I could trade you a few buckets of your soil for a few of my super dense clay & caliche, it would solve your drainage issues...

Anyway, lots and lots of organic matter mixed in will help. It will soak up your water and stay moist longer than your soil. When you plant something, over excavate the area, maybe bigger than you anticipate the roots spreading, and backfill with a high ratio of organic matter amendments mixed with your soil. If it is permaculture like your citrus, seasonally mulch with more organic matter on top. It should make a big difference.