Just barely cover the soil with the cornmeal. If you put too much down it forms a crust. After you water a couple of times it disappears and I like to add a little more. You don't need it once the plant gets some size to it. If you have problems with mold and mildew just put a cupful into an old sock and place the sock into a gallon of water. Let it sit for a day or two and use it as a spray, either as a remedy or a preventative. If you maintain a spray regimine on cucurbits you will not get powdery mildew which plagues most squash and cucumber growers. Corn gluten meal is a LOUSY weed preventer because you must know the time on the calendar when the seeds will germinate and that is just about impossible. It is a much better nitrogen source with a N of about 10 than anything else but the cost of the stuff makes its use as a fertilizer rather cost prohibitive and never ever use the stuff with seeds or very young plants. If you incorporate leaves or any organic matter into your soil, if you spray the soil heavily with 2 oz molasses per gallon of water you will find that most if not all of the incorporated material will have been completely composted over the winter. On all of my vegetables I use molasses at least once every two weeks and if letting the soil rest for the winter I add a lot of oak leaves, turn them under and spray molasses heavily. By spring planting time my soil is always light and fluffy and not a leaf in sight. You cannot go wrong using molasses. It does nothing directly for plants but it GREATLY enhances the numbers of beneficial soil microbes.
Greensand is a mined product from ancient ocean beds. One mining spot will be different from another but all are good, all are chock full of minerals. I don't know what rock dust is. Is it just some rocks someone pulvarized? I was speaking of Rock Phosphate. I use it to enhance bloom numbers in tomatoes and peppers. Rock phosphate is NOT interchangeable with Greensand as RP has a high phosphorus content and few other useable minerals, whereas Greensand is full of all trace minerals plants need. Greensand though is getting scarce. There are others on the market which I haven't used. There is even a Brownsand that is supposed to be excellent.
The best thing is to use a better draining mix. And if you can control temps and humidity like indoors that is high tech.
