Sand is the predominant soil type in Florida. While sand on beaches or in zen gardens may be wonderful, pure sand is not conducive to growing most types of plants.
Florida sand has no nutrient value, and very little mineral value. It does not hold water well, and is a host to a very large nematode population. In short, unless you're planting nothing but natives, planting in Florida sand requires adding organic matter (compost, leaf mold, etc.) to get plants to thrive.
Adding Organic Matter is the Key when Planting in Sand
In my experience, when planting in sand, the best ratio of organic matter to sand is 3 to1, or 75% organic matter to 25% sand. Adding organic matter in this ratio converts pure sand into a sandy loam, which will hold enough moisture, while still providing proper drainage, giving proper nutrition, and keeping the nematodes under control.
When planting in sand, you will use one of two techniques. If you are planting a large area, you will want to mix the organic matter into the sand. Of course, if you are adding 75% more than what is there, this is going to raise the level of the soil unless you remove some of the sand beforehand. My favorite way of adding organic matter is to dig out to about 12 inches deep, and layer the organic matter three times with 3 inches of organic matter to 1 inch of sand. It will still be a little above ground level, but the sand will very quickly filter down into the organic matter, and it will level out. This saves a lot of work mixing the two in place. Digging down the required 12 inches is easy except for the sand collapsing in on itself, which I address below.
Planting a Single Plant in Sand
Planting a single plant in sand is easier. First you need to wet the sand so it will not collapse down upon itself while you're digging. Dig a small hole and fill with water and let sink in. Do this two or three times until the sides are saturated enough so that they don't collapse while digging. The water won't want to sink into the sand at first, so to decrease the surface tension, add some liquid dish soap to the water. The soap acts as a surfactant to make the water "stick" to the sand.
Once you have dug a hole that is two to three times the width of the plant rootball and 3 inches deeper, put 3 inches of organic matter into the bottom, add the plant, fill the hole with water, then layer as above, with 1 inch sand and 3 inches organic matter. To help roots establish, sprinkle 1 cup of epsom salts around the plant , from the trunk/stem to the drip line, water in, and mulch.
Maintaining the Organic Matter to Sand Ratio
Organic matter eventually breaks down, so adding organic matter each year will ensure that your plants continue to thrive. This can be done by simply spreading compost about 3 inches deep from right past the trunk to the dripline of the plant, working it into the top inch or two of soil, and mulching. After a few years, you will notice that the soil is very friable (crumbly) and rich; nothing like the sand you once had there.
Now your plant will be able to grow and thrive, and when it grows out past the amended soil, it will be strong enough to survive in the sand around it.
Image credit: Horton Grou via sxc.hu