Deep soil fungus/bad soil killing my plants....want other opinions.

    I live in the northern hemisphere and recently moved into a condo complex in July. An unused full south garden space was just calling out to me so I claimed it for my own. I planted about 10 tomato plants and 8 of them died. In the unused space I found rotten tulip bulbs with mold growing all over them. I removed the bulbs and planted my tomato plants. I cut green bamboo and stuck it in the ground as stakes at roughly the same time as the tomatoes. Things went fine and then a month later 1 plant died......it just wilted away overnight. Then another. While picking weeds I decided to pile up all of the pesky invaders around 2 of my living tomato plants......they were all wilted the next day. They died soon after. I looked at the bamboo stakes and it was all soft and wilted with white areas at the joints. I removed it. One of my other tomato plants started to wilt and I quickly piled dirt from another area of the garden around it and it has survived...although it isnt growing well. I am certain I have a fungus living in my dirt(not yet soil) and have a plan to eradicate it....but am not sure about the chemistry behind what I will do.
    I want to use a Sodium Percarbonate solution(a base) to kill all of the mold and then I am aware it will leave me with a soil way too high in the PH range to grow tomatoes. To amend this I want to add a citric acid(or oranges as they grow everywhere here and I can get them for free) and clean adjacent soil with all of those good microbes to balance things. will this work?
    I have 5-6 months before I can plant my next summer garden.
    Where I am living right now(not in an English speaking country) I cant buy soil PH testers so I will have to use either a vinegar/baking soda or red cabbage tester to get it right.

Interesting situation.  I don't know much about the fungus side of things, but I'm sure someone else will be along soon to talk about that.

It does remind me of a situation I had once, where everything rotted and got the white fungus on it.  Instead of dealing with the fungus directly, I decided to go a step further and try to find out why the fungus liked that location so much.  I discovered that the drainage wasn't very good.  This may or may not be your issues, but what I did was to take the top soil, move it to one side, fluff up the subsoil with a fork, then build raised beds.  Put down a layer of compost (in my case raw kitchen scraps) then replaced the topsoil (which had been laying in the sun for a few days).  Never had the problem again.  Like I said, your situation may be different.

Getting rid of the offending fungus is one option.  Have you given any thought as to what you will replace it with?  It's a bit like pasteurising milk - if you just leave pasteurised milk in the fridge it goes off, but if you put some yoghurt in it, it last longer and goes a delightfully sour taste instead of putrid rot.  I'm thinking about the soil, one thing I've seen is people kill the offending fungus/bacteria only to have it come back.  Other people take steps to replace it with new bacteria and this seems to make a longer lasting solution.  Some people even skip the step of killing off the offending stuff, and just add new fungus/bacteria/microbes/whatever, which drive away the unwanted pathogens.  I like this last method because I'm lazy and it skips a step.

Seems to me like it is a problem with too much water. Might try planting cattails there, or some other type of swamp plant.

Paul the first thing to do now is dig an exploratory hole in the ground, go down at least two feet deep.

See how much water comes into this hole and how fast it fills.  Your problems seem to be from lack of drainage in this bed, and the test hole will tell you if this is indeed the case.

I do not recommend the use of sodium percarbonate (this will add high salinity and perchloric acid to the soil and you will have a hard time remediating the two for future planting.
Calcium carbonate might be a better way to go if you find out that you do indeed need to do something other than improve drainage.

You didn't mention doing a culture to make sure the molding bulbs were caused by fungi in the ground. To test that you would need to culture soil samples from each 6" depth, it will also allow identification of the culprit (s) if any.
Bulbs will rot from to much ground water, tomatoes will die from to much ground water, bamboo will rot from to much ground water. At the same time molds and other fungi can thrive in to much ground water for other plants.
Which can make folks think it is the mold/ fungi that are to blame when in reality it is the over wet condition of the soil that is creating all the problems.
This is an almost normal set of conditions for areas such as you have mentioned, Condos with unused garden spaces.  Also be on the look out for a silvery substance since it is very possible that the builder used donna fill for the stabilization of the foundations and as a substrate for any parking areas.
If you find that substance, raised beds, with a barrier between the current soil and the fill for the raised beds will be the best solution.

If you can give me more information about this garden spot, I can be of better help.

Redhawk