Seashells? This is not a problem I face in my yard.

Used mushroom substrate is a great way to add organic matter and also sweeten the soil. This type of soil is usually very alkaline. Adding organic matter also increases the "buffering" capacity of the soil so that definitely helps also.

I don't know if the "Mushroom Compost" you can buy in bags is the same thing or not. I have been "attempting" for a year now to get stands of clover growing where I'm at, and dread the thought of adding lime, oyster shells, wood ashes, etc.

"dread the thought of adding lime, oyster shells, wood ashes, etc."

Why?

Well for me it's mainly the cost, and of course the glaring uncertainty that it may not improve the soil situation for a stand of clover. It's just easier for me to find another kind of cover crop to grow to improve the soil, and dream of growing clover some other time. :)

Speaking of what we're growing - what are you trying to grow that you need to alkalize the soil? How big of an area?

Only a small bed. Pentas prefer a more neutral soil type than what I seem to have (I have not tested the soil ph yet). From what I have read, Pentas leaves will brown at the tips if the soil is overly acidic. As my pentas plants are otherwise healthy... or were at the time of the original post, not now after the frosts... I took their browning tips to mean the soil is a bit too acidic for them. Since I also have Indian Blanket which also prefers a more neutral soil, I thought I would plant both of these in the same 3x4' bed (estimated) and slowly amend the soil in that area to raise the ph, using the pentas's leaves as an indication of when the soil is 'just right'.

I would have the soil tested before trying to change the PH. They can do it at the extension office for a couple dollars

Wood-ash could easily be free, just burn some oak outside in a fire-pit on cold nights. The K and P and carbonate are quite good for most plants within reason, and certainly for clover.

Particularly in florida sands with such low OM content, definitely get hold of some well-decomposed OM to mix the ash with before adding. The more char is in the ash the better, however, bear in mind that char is highly attractant of minerals in the soil which already are in low supply. The fly-ash releases right away, and that is the stuff that raises ph and provides K, notably, and some P. Those effects leach in sand and so are short-lived. So often I sift the ashes through a screen to separate the char, then soak the char in manure tea, urine, and any kind of solution that will be brimming with minerals to "charge" it and become a slow-release source of minerals to the soil system.

Here in Miami our soil is so alkaline it's unbelievable. It's from all the limestone that we live on top of. There's actually no way to lower the soil pH here. You can't even get a proper soil test because the pH is so high it's impossible to test (according to the lab at UF). Makes for some interesting challenges in getting mobility with micro-nutrients.

pako, do you see the effects of this in attempting to grow crops? Legumes should do pretty well.