Soil prep

What would be the best medium to add to sandy soil to help hold moisture?

10 inches of sandy loam topsoil and 48 inches of sand underneath. :(

A plastic bag... Just kidding. Peat moss and black earth without sand as you have enough. Any organics you can get. leaf mould, compost, plastic bags, oh wait, forget that last one.

I agree with the above ...I am a big fan of aged cow poo....it goes into almost everything! holds the moisture and feeds the worms...promotes good friendly microbes

I use crushed dolomite lime stone from the big box stores on my soil which is sandy. Don't use it around gardenia, azalea or any acid loving plant. It will help add calcium to your soil and helps to bind loose sandy soil, creating loam. If you can find it, there is a product called 'essiential minors' or trace elements that is helpful too. Lightly and frequently is my recipe.

And lots of compost

It depends on what you want to grow. If you like wildflowers and dryland plants, just top your sandy soil with 4 to 6 inches of sandy gravel. It's amazing how well it retains moisture.

If you like vegetables, hybrid garden flowers, and wetland plants, you'll need to buy topsoil and make compost to dig into your beds, to supply nutrients and increase moisture retention.

So rotted organic matter? This is for a vegetable garden.

I had dumped a truckload of seasoned chicken manure in one plot, and I have been plagued with pigweed ever since (never had it before.) I did the same with cow manure and have been fighting lambs quarters since that experience. I really do not want to introduce any more pests.

Those weeds are easy to kill with a lawn weed killer if you aren't opposed to using chemicals. But you are right. No matter what you add to your soil, you are taking a chance of adding whatever weeds grew in that area or whatever plants the animals eat as they can pass seeds. BUT... you have to weigh the good vs. the bad. As I said, weeds can be killed, but sand can't retain moisture, nutrients, etc...

Hambone,

When using uncomposted manure all you have to do is spread the manure and cover with black plastic. Let it sit for a couple weeks to a month and the seeds will be cooked and you weed problems should be considerably less. This is best done in the summer months, for you I would think that would be from mid-April on to Oct. If doing it in the cool months allow 6-8 weeks for the black plastic to work its magic. You can cover your plots when not in use, with plastic, and get rid of a lot of soil pests, weeds and disease.