About the only material that can, and should, be added to any soil without a good reliable soil test to guide that addition is compost and other forms of organic matter. If you were to add some form of synthetic fertilizer and the soil did not have adequate levels of organic matter those nutrients would simply flow out of the sand and not be available for the plants anyway.
Organic matter also helps hold moisture in the soil and watermelons need a lot of water to grow well.

Thanks kimmsr. So basically what you are saying is that what I was thinking about adding would be fine?

Even if I can't find a source of compost in bulk the bagged 50/50 mix is supposedly half compost/half manure. I think that would fall under "compost and other forms of organic matter."

I wasn't planning on adding any synthetic ferts just organic granular like dr earth or espoma organic garden-tone and mixing that in with the compost or the 50/50 mix and the existing soil.

You might want to consider drip irrigation-that method would cut your water use, and keep the watermelons hydrated, at the same time. Once the plants are established, it helps to mulch them with shredded leaves or something similar. That will keep the weeds down, and also reduce evaporation of soil moisture.

Contact your County's Extension Service office as they likely have the info you need.

To locate your county's office, use this interactive map:
http://www.csrees.usda.gov/Extension/

Here is a link that might be useful: Locate the county's Extension Service office

There have been many discussions about this topic at the florida forum on GW; searching the subject there will bring up quite a lot of specific info for florid sand.

I would not bother with a 50/50 mix of compost and manure and would instead opt for just the compost, at least until I had the results of a good reliable soil test.

thanks everyone.

There should be places where they sell bulk garden soil, mulch, compost, gravel , etc. One cubic yard of compost ( =~27 cu-ft) cost around $40., if you take delivery. One cubic yard can be spread over about 100 sqr-ft garden area at 3" thickness.

BTW: by looking at the the subject plot, and from the weeds that are currently growing in there, you should be be able to have a good estimate about its fertility. Take a handful, and check its composition .. You will need to plant thing in it and listen to your plants/patch. Your plants will mirror the state of the soil.

seysonn said, " by looking at the the subject plot, and from the weeds that are currently growing in there, you should be be able to have a good estimate about its fertility"

Please clue in those of us that have been at this gardening thing for 60 plus years and have found that plants do not always give good indications of soil fertility. Many "indicator" plants have adapted and will grow quite well in soils that a while back they would not grow in at all.

I'd use the compost and/or manure at this point, but unless you're planting now, save the granular fertilizer for the growing season.

I'll be adding the compost about mid Jan and sowing the watermelon seeds about 30 days after that.

IME of central florida and gardening in small areas, areas that have been amended are quickly over-run by whatever aggressive plants are in the area. These will often show a difference in being larger and more healthy-looking than the same plants nearby. For example, I'll come down in the winter time from being away for ten or more months, and a plot may be over-run with bahia grass. The bahia grass in heavily amended areas will be much thicker, taller, and greener. The surrounding grass will be brown from drought while in the amended area clearly it has gotten much more moisture in addition to nutrients. Similar effects can be seen in a common invasive weed such as beggar's tick. In amended areas it may be 5-7 feet tall while in other areas it will be 2-4 feet tall.

Of course, the old plot belonging to the OP is very unlikely to have been amended in a way as to have such a long-lasting effect.

Please clue in those of us that have been at this gardening thing for 60 plus years and have found that plants do not always give good indications of soil fertility. Many "indicator" plants have adapted and will grow quite well in soils that a while back they would not grow in at all.( kimmsr)
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I just did give you the clue but you didn't get it.

I am close to 70 years old, born and raised on the farm.
For your information, weeds are also PLANTS. From the vigor, size and types of the plants you can get some estimate of the soils fertility. I am sorry, but all you can do is to send a soil sample to a lab to find that out.

"Weeds" are plants we do not want growing where we do not want them growing. Old school thought was that dandelions grew in compacted, low fertility, acidic soils, but as most gardeners today know they will grow really well anywhere. All of the other so called indicator plants have also evolved to grow wherever as some of us have learned in the last 60 years.
Even if indicator plants might indicate that the soil is acidic you will not know why or what is needed to correct that problem without that good reliable soil test. People that argue that soil tests are unnecessary because out ancestors did not have, or use, them probably should also stop using electricity and natural gas, drive cars, or fly anywhere. Use the technology available today to help make our lives better without doing harm to others.

Kimm, your point is pretty valid for most parts of the US/Canada, but like a lot of your advice, off target for most of florida.

Peninsular Florida is unique, I believe, in most of north america in regard to soil types. What is especially unusual is the relative lack of variation. In most regions soil type can change dramatically over a very short distance. However, in FL, for the purposes of raising annual crops, there is effectively no difference. The only real factor that changes a lot is elevation, with low areas tending to be poorly drained or totally saturated, these areas are of course not good for vegetable production.

Areas that do not flood in heavy rains are well to highly drained sands, and these are reliably very poor in nearly all nutrients. A soil test doesn't hurt but is not necessary unless one suspects contamination. For example, areas that were used for citrus formerly typically have high copper and maybe other heavy metals as well. Such areas are usually near lakes in central florida. Lakes therefore can be contaminated with heavy metals from years of fungicide and pesticide use. In florida therefor it is more useful to test water than soil.

It is an absolute that unaltered sand in florida will need lots of OM, N, K, S, and most of the traces to grow crops (including citrus). Calcium is usually low in central florida but not as low as other nutrients. P is the one macro that is adequate naturally. Aluminum is always high.

Note to self, avoid telling a 70-yr-old farm boy halfway across the country how things are in their neck of the woods. :-D

Most everyone, from professors of soil science at the University of Florida to "garden gurus", that I have found and read tell me that the best thing one can add to the sandy Florida soils is organic matter. Without organic matter to help hold both nutrients and moisture in those Florida sandy soils only locally adapted fauna will grow and some Florida gardening gurus suggest doing just that. That, however, would limit what could be grown and the large vegetable farms probably would not exist.
There are a few of those with phD's in soil science that will tell a Florida gardener to forget adding organic matter to the soil and instead build raised beds and filling them with something called "topsoil".

Here is a link that might be useful: What to add to /Florida soils

I'm not suggesting that your advice to add OM is a problem - one cannot hardly ever go wrong doing that, and certainly not in impoverished sand. It's your insistence that getting a soil test is critical.

Peninsular florida is one place where getting a soil test is generally unnecessary for a vegetable gardener, for the detailed reasons I gave above and which you most likely did not read.

I tend to go with what pm says here. Most of Florida is very sandy and therefore usually lacking badly in organic matter AND minerals. I would add lots of organic matter that is well rotted. I would also add organic fertilizer like Plant Tone for season long fertilizing, AND in this case I would add some banded more 'chemical' fertilizer to boost the plants from the get go.

When we really come down to it, there are actually very few things that we truly need in our daily life. Whatever we don't have access to we make do. Whatever we have access to we utilize it as best we can. Of course soil test is not so critical as a life or death thing but it sure is great to know about your soil in depth. If it is not that important to you then to each his own.

What I was addressing was KaOttic's situation right now for seeds to be sown almost right now.

The same people that strongly suggest adding organic matter to Florida soils also strongly recommend soil tests since that sandy soil allows nutrients to get washed away easily which will then pollute the ground water as well as the streams and lakes. Nutrient pollution of the Everglade is still a large problem because of the amounts of "fertilizers" commercial growers pour on their land.
Soil testing is a tool that allows reasonably intelligent people to know what their soil needs which can result in saving money as well as lessoning potential pollution.

kimmsr, Granted that soil tests can be very helpful, BUT to address the op for planting very soon for watermelons, I think that adding some fertilizer in that Florida sand is pretty safe for now.

Kimm, you clearly have not gardened in central florida.

At the same time you are not being consistent between your posts. The nature of decomposed OM is that it reduces leaching, as we all know.

If you toss a highly active organic fertilizer or a high-index salt fertilizer into a low SOM sand then of course it will leach away in heavy rains. Of course, another thing you probably don't realize about florida is that heavy rain is extremely rare during winter, so leaching isn't a concern unless one was irrigating regularly in very incompetent manner.

Anyway, hopefully the OP can gain some use from this thread before devolves into the usual situation of you insisting that you know all about every climate/soil paradigm in the world.

No, Mr. Brown, I have not spent enough time in Florida to garden but I do have several people that I correspond with that do garden in Florida who all tell me that they have had success gardening only because they added organic matter to the soil they have. Just like the professors of soil science at the University of Florida strongly suggest be done.

Jeez, it's like talking to a wall, isn't it?

Nobody is challenging the "add OM" part, in fact, that's what we all recommend.

It's your insistence that one cannot reasonably add other things to florida sand without a soil test that is off. For the reasons I have stated, and again, which I doubt you read. It's seems clear to me that you don't read other people's posts in any detail.

Mr. Brown, I have never stated that one could not add "other things" (presumably fertilizers) to any soil, much less Florida sand, without a soil test. I have stated that one should not do so without a soil test because of the potential for polluting the water, wasting ones money, or creating more problems by creating a nutrient imbalance in the soil.
If protecting the environment, saving money, or advising people in a way that might prevent future problems is "off" then that is where I am.

If someone was ready to plant a few seeds now, I would not burden them down with the whole magilla, but I would try to advise how to 'more likely' have a decent result now. Soil tests and other advice is good, but I don't see that as necessary immediately in every case. And.. I don't see every small plot as ruining the environment.

"I have stated that one should not do so without a soil test because of the potential for polluting the water, wasting ones money, or creating more problems by creating a nutrient imbalance in the soil."

And I rebutted those points, precisely, for the average situation in central florida drained sands, but you don't know because you did not read or at least did not pay any attention to it.

I suggest this is because you do not like to address the certainty that your one-dimensional standard advice package that you give out on these forums is in some circumstances not helpful. When those circumstances are pointed out, you keep repeating the same thing, as you are doing now.

I would have left it be long ago except it's such a dis-service to the neophytes in those particular circumstances where your advice does not apply, like this OP. BTW, digging up UF bulletins designed for large-scale vegetable growers producing markets crops on plastic and fertigation does not help someone who wonders if they can grow some backyard veggies without getting a soil test.

Well Mr. Brown, I think I would listen to the soil scientist, horticulturist, and botanists at the University of Florida who have done much more research on growing plants in Florida then I have about how to grow things and they will tell you to do what I have written here.

Hopefully I can put an end to this... there was never a question about getting a soil test. As I clearly stated in my OP, I will eventually get one. What I was trying to find out was what I could safely add to this florida sand that would generally be ok without knowing the results of a soil test, just so I could go ahead and get started with the watermelons a month after I moved into my new place.

My biggest question was that if I could not find a local source of decent compost, if adding bagged 50/50 compost/manure mix would be ok and I think that was sufficiently answered.

One thing I wasn't necessarily clear about in my OP was that I was wanting to keep this organic if I am able to, so ground water contamination is not as much of a worry. The only thing I will be adding besides compost and/or manure would be a granulated organic fert, which I was thinking of digging in the same time as the compost/manure so that hopefully some of those nutrients will be available by the time the seeds are in the ground a month later.

I appreciate everyone's comments and advice.

Aaron

Aaron, if you are willing to spend the money, you can probably find some organic certified bagged compost at a box store.

I'll tell you this little story:

Last winter I noticed a remarkable patch of collard greens growing in a large garden by someone's house while walking around the neighborhood (central florida). I struck up a conversation with this friendly older gentleman to find out how he had achieved such a fine stand of mature thriving plants, and they were clearly not in boxes of bought compost as most florida gardeners do (and which generally have problems).

He bought them as seedlings at a box store in november, stuck them in the sand and fed them a bit of ordinary chemical veggie fertilizer to get them going well. Then he mulched with leaves that he gets dumped by the town. Keeps mulching, and mulching. Florida sand eats mulch. He had a good foot of mulch on there, I dug down in it and the bottom part was damp and black. No easy trick in florida.

He just piled on the mulch and the plants went nuts. Best-looking collards I ever saw.

Interesting.

Money is an issue and I'm not that hardcore organic kind of guy. Most of what I buy at the store is not organic, mainly because of the price. I'd like to try and keep it organic in the garden though, if possible. If for no other reason than it gives me a little piece of mind and helps me justify spending money growing food instead of buying it.

This will be my first major garden (at least 30 containers plus the in-ground stuff) and my first time doing anything in-ground so I'll be doing a little experimenting. If I'm unable to find a way to do it organically, then so be it and I'll cheat if I have to, but what the hell, I'm going to try.

That initial shot of fertilizer didn't have to be synthesized, it could be any good quickly-available source of N&K (like urine). The point is, in florida sand, a growing crop must have fertilizer added just before or at planting and again once or twice until the plants are quite large or cool temps make growth slow.

This is why I was saying there is no super-pressing need to get a soil test - in florida sand N&K (and S and a wide spread of micro's) are guaranteed to be insufficient.