Since no one answered your question directly, you can get muriatic acid in any pool supply store. Make sure to read EVERYTHING about it before you play with it. Do a test run in a place where it is not going to be too visible if it turns out to be damaging on the learning curve. Have plenty of protective gear, lock your pets away, have your kids go to grandma's, protect any vegetation that you don't want to end up dead. Have a plastic bristle brush ready to scrub the bubbles off to see the results before you wash it off. It's a lot to think about, but it can be very rewarding if it is done well. I work in the office for a Construction and Maintenance Company here in Los Angeles and based on the hands of the guys that do only this kind of jobs I'd say that those jobs are not for do-it-yourselfers. But by looking at how they do it and how nice and clean concrete surfaces became, I bought the materials and did my own driveway and it turned out to be like new! Here is a link that might be useful: Look up acid wash on this website.

Given the size of the gardens and the amount of stuff you have, I don't think there's any real problem with most of it, especially if you mix it well and distribute it evenly. The soybean and alfalfa meals in particular will provide nitrogen to break down the carbon in the sawdust. Given the fine structure of the materials, I'd mix it all and set it aside to compost a bit while building the bottom layers of the bed with coarser materials, then put the fine stuff on top. With a 46 foot long bed varying in width from 4 to 8 to six feet (I'm assuming that's what you meant when you said "deep"; I can't imagine trying to pile up a lasagna bed eight feet thick from base to surface), your surface area is somewhere in the vicinity of 275 square feet; the recommended rate of application for the sul-po-mag would be about 2 1/2 pounds for that area. So maybe add half of what you have, and save the rest for another year. You don't say what kind of lime you have, but 3 pounds over the area you have is about the recommended rate even for the most concentrated lime (10 lbs for 1,000 sq feet). The thing is, it may not be necessary unless the soil in your area is generally acid. Lasagna beds, which are mostly compost, generally wind up with a neutral pH anyway. Assuming you have a lawn, you might be better off spreading it there - liming is usually recommended for turf grasses, not for gardens.

Ox - I was doing some research, using the search function, when I came upon this thread and realized as I scrolled to the end that I never answered your question. Just saying that you use MG isn't enough information. MG manufactures several soluble ratios. 20-20-20, 24-8-16, 12-4-8, 10-30-10, 10-52-10, 30-10-10 are all soluble MG products. The ones most fig growers are apt to reach fore are 24-8-16 (best choice) or 20-20-20. Your assertion that you would be over-applying P is correct if you are using anything but 24-8-16, 12-4-8, or 30-10-10, and the latter is inappropriate for figs in containers because of its high N content in relation to the other macro-nutrients and it's acid reaction in the soil solution. If you ARE using either 24-8-16 or 12-4-8 (the same ratio - 24-8-16 simply contains more of the 3 primary macros by weight than 12-4-8) you are supplying P in almost exactly the correct ratio. The P in fertilizers is not reported as elemental P, instead, it's reported as P2O5 (phosphorous pentoxide - K is reported as K2O). To find out how much P is ACTUALLY in the soil, we need to use a factor of .43 for the middle number. When you multiply the P in 24-8-16, you get 8 x .43 = 3.5. Taking this 1 step further, and recalling that upthread I said that plants use about 6X more N than P, dividing the amount of N in 24-8-16 by the actual amount of P (24/3.5 = 6.8) we find that MG 24-8-16 has 6.8 times as much N as P. The amount of K similarly follows the amount of K in relation to N as being provided in almost exactly the same ratio in which plants use them. Some would have you believe there was no thought that went into deciding on the ratio fertilizer manufacturers chose as their 'all-purpose' fertilizer, but from these quick calculations you can see that they provide nutrients in as close to the ratio plants use as you'll find in any commercially available fertilizer. It was no accident. Now your questions about fertilizer phosphate: The phosphate in fertilizers is initially quite soluble and available. Most phosphate fertilizers have been manufactured by treating rock phosphate (the phosphate-bearing mineral that is mined) with an acid to make it more soluble. When the fertilizer or manure phosphate comes in contact with the soil, various reactions begin occurring that make the phosphate less soluble and less available. The rates and products of these reactions are dependent on such soil conditions as pH, moisture content, temperature, and the minerals already present in the soil. This chance to an insoluble form is MUCH less prevalent in container soils because of their relatively low bulk density and high organic content. As a particle of fertilizer comes in contact with the soil, moisture from the soil will begin dissolving the particle. Dissolving of the fertilizer increases the soluble phosphate in the soil solution around the particle and allows the dissolved phosphate to move a short distance away from the fertilizer particle. Movement is slow but may be increased by rainfall or irrigation water flowing through the soil. As phosphate ions in solution slowly migrate away from the fertilizer particle, most of the phosphate will react with the minerals within the soil. (Again, this is in MINERAL soils, and not so much in container media.) Phosphate ions generally react by adsorbing to soil particles or by combining with other elements in the soil, forming compounds that are solids. The adsorbed phosphate and the newly formed solids are relatively available to meet crop needs. Gradually reactions occur in which the adsorbed phosphate and the easily dissolved compounds of phosphate form more insoluble compounds that cause the phosphate to be become fixed and unavailable. Over time this results in a decrease in soil test P. A general sequence of reactions in alkaline soils is the formation of several compounds that result in a decrease in solubility and availability of phosphate. Each of these reactions will results in very insoluble compounds of phosphate that are generally not available to plants. Adding to the active P pool through fertilization will also increase the amount of fixed P. Depleting the active pool through crop uptake may cause some of the fixed P to slowly become active P. The conversion of available P to fixed P is partially the reason for the low efficiency of P fertilizers. Most of the P fertilizer applied to the soil will not be utilized by the crop in the first season. Continued application of more P than the crops utilize increases the fertility of the soil, but much of the added P becomes fixed and unavailable. An important aspect of the ability of a soil to hold phosphate is that a soil cannot hold increasing amounts of phosphate in the solid phase without also increasing soil solution phosphate, so there is sort of a threshold. Increased amounts of phosphate in solution will potentially cause more phosphate to be lost to leaching through the soil - especially in container soils, another very good reason not to over-apply P. You asked: "If we water to the point that our pots drain, would it be wise at some point to simply provide nitrogen alone?" I would give a qualified 'NO' to that question. For us hobby growers, I don't think it's ever a good idea to provide singular elements as a fertilizer unless it's part of a well-conceived plan. When you start second guessing what you're seeing in your plants ...... well, even the experts are often fooled and misdiagnose deficiencies and related problems. We might see yellowing leaves caused by a high level of soluble salts in the soil or over-watering and conclude the plants need N, which only exacerbates the issue. I don't think it is reasonable to apply urea and wait for other deficiencies to be revealed. I think that if you are absolutely sure that all other nutrients are in the soil at adequate levels and in the right ratio and N is the only element shown to be deficient, then applying urea would be the correct thing to do, but absent that knowledge, I would stick tightly to using a 3:1:2 ratio fertilizer and flushing the soil regularly so that ratio in the soil solution isn't skewed by accumulating salts. If you CAN'T flush the soil regularly w/o risking root rot, I would take a hard look at my soil choice and switch to a soil that DOES allow you to water that copiously. Sorry I missed this, Ox .... and sorry for the length of the reply. ;o)

Those tend to be very porous and probably won't take to the acid stain so well. They're made of concrete, but it's not the same mix, these are dryer, therefore more crumbly. Poured concrete (the fake stones, counters, floors, statues, etc) is a different mix so it has a smoother 'shell'. That shell is etched with the acid and the color adheres. I've not tried to acid wash this type of concrete product but, you could try one and see if you like that. To get an idea just try diluting some water based wood stain, brush it on, then let dry. If you like the effect, try acid stain. Or, you can just leave the wood stain and put a clear sealer on it if you want the color to stay. It's easy to reapply later, tho. I'm the wife of a decorative concrete guy...so I get to see all his experiments with concrete coloring. He's been using this new stain that he mixes with the muriatic acid that looks like rust. It's really cool, and I'm considering trying it out on the stone fence I have in the back yard.