The 1st and 3rd are faster acting limes. You will get a pH adjustment quicker than you would with ordinary lime (2nd in your list). You also use much less product per application. Ordinary lime takes months, even years, to work. The good side of that is that it is still working for years. How much did the soil test say you need? What you might consider is doing a fast acting lime now and doing an ordinary lime in late fall. If you use the fast acting lime, foliow the directions on the bag. Depending on what the soil test said you needed, you might be applying lime for a couple of years. For ordinary lime, don't apply more than 50 lb/k at a time. Another factor that might weigh in your decisions is whether you need magnesium or not. If you are low in magnesium, the dolomitic lime will supply some. If you are high in magnesium, you probably want to avoid it. There is also ordinary lime that is calcitic, not dolomitic.

Thanks for the info. I need 25 lbs/1000 sq feet in my front yard (which is 10,000 sq ft, so I need 250 pounds, half now and half in 6 months or next spring), and 150 pounds/1k in my back yard, which is 8k sq feet, so 1,200 pounds!!! Front yard is 5.7 but back yard is 4.5. This is why the cheaper the better...

Also, Mg is slightly low, so I don't mind adding more.

You could do the front yard lime all at once if you like (using dolomitic). Or break it into two applications if you prefer. The back yard will need three applications at 50 lb/k (or more applications if you prefer to do less at a time). Spring and fall are good times to do it. Keep it at least two weeks away from any fertilizer application. Water it in. The faster acting lime is faster acting because it's ground up very fine and then pellitized to make it easier to spread. Because it was ground up so well, it dissolves faster and thus gets to work faster. It's my understanding that you still need the total amount of lime indicated in the soil test, whether it's the slow or fast kind.

Thanks so much for the info!

Quick follow-up; a local garden center told me that their fast acting lime (30 pound bag for $14) covers 5,000 square feet, and the 'regular' lime 40 lb bag covers 1,000 sq ft at $5/bag. If that's true, a) do I need to factor in the different coverage ratios when figuring out how much to use (or simply go by weight as the soil test only tells me how many pounds I need) and b) if going by sq ft coverage, the fast acting is actually cheaper, as I'd need 5 bags of regular to equal the same sq ft coverage as 1 bag of fast acting.

The fast acting at Lowes also says it covers 5,000, and another site had regular which said it covers 4,000.

So confused now :(

The garden center fast lime is supplying 6 lb/k (30 lb÷5k). That may be the upper limit on how much can be applied at a time for that particular product (it it may be the average rate--have to see the instructions on the bag). You get a faster response but still only 6 lb/k of lime. The regular lime there gives you 40 lb/k (your front yard needs 25 lb/k, back needs 150 lb/k but not more than 50 lb/k at a time). They are using "coverage" to mean what they recommend putting down at a time. It has nothing to do with how much lime you need. If your pH is very low, maybe you might like to get it up quickly and you might want to do at least one application of the fast lime. If your pH is okay (at least 5.5) and the lime is just to get you to a better target pH, there is no rush and the slow lime will be fine.

In addition to what Becky has given you:

Your lime recommendations are based on a certain quality of lime product. Lime is rated based on calcium carbonate equivalency. The highest quality/purest calcitic limestone has a CCE rating of 100. This CCE rating will be listed on the bag unless your State requires another rating system to be used.

You will need to know what quality of limestone that the number of pounds of lime that your test recommendation is based on. (university soil test labs often give recommendations based on the quality of the lime that is mined locally). For instance, the lab recommendation might be for 50#/k of an 80 CCE lime. If the CCE of the lime at your garden center is 100 CCE, you would only need 40#/k of the 100 CCE lime to neutralize the same amount of acid as 50#/k of the 80 CCE lime. If the lab's recommendation is for 50# of a 100CCE lime and the Fast Acting lime has a CCE of 90 (common for fast acting limes), then you would need to apply 56#/k of the Fast acting lime to have the same effect. There are charts on the internet to help make these conversions. Just a consideration.

Hi. Follow-up on the lime; does regular pelletized lime 'last' longer than fast acting? In other words, can I do regular lime (a lot of it) once or twice, and then I'm good for a few years, whereas the fast acting I have to keep doing each year? Also, same question for things like Mag-i-Cal and Solu-Cal; do that have to be applied each and every year to maintain the pH, whereas regular lime might be good for a few years?

Yes. Lime is lime. Some of it is faster acting, some is slower acting. MagiCal and SoluCal are examples of faster acting limes. If you need a 100 lb/k of lime, for example, you can do two applications of regular lime at 50 lb/k and it should suffice for the next few years. If you choose a fast acting lime that could be applied, say, at 10 lb/k, you would need 10 applications. That's assuming both limes have the same CCE (see Ridgerunner's explanation above). You can mix it up if you like. Using the example of needing 100 lb/k (and the limes have the same CCE), you could do 10 lb/k of a fast acting lime now and get a pH change within weeks and do 45 lb/k of regular lime in the fall and 45 lb/k next year. Do you know the CCE of the lime that the lab is recommending? If it's not in the report, you could call and ask. The bags of lime will have CCE ratings on them.

Just for clarification.

A Soil Buffer pH test determines how much of a base/alkaline substance, "lime" needs to be applied to neutralize acidity in a unit of soil to raise the soil pH to a desired pH (say 6.5).

To my knowledge, there is no standard defining "Fast" acting lime.

The finer that limestone is ground up, the faster it will interact (more surface area is exposed to the acid in the soil solution with fine particles vs large particles) with the soil acidity. "Fineness" is measured base on the screen mesh size that it will pass through. A 40 mesh grind is larger than a 300 mesh grind, therefor a limestone that is ground to 300 mesh will "dissolve" faster than a 40 mesh. Because ground lime is powdery, it is formed into pellets for ease application. Ideally, for even coverage and homogeneous change, spreading the powder would be the most effective, but no one wants to deal with the mess. FYI, studies have shown that there is no significant difference in the speed of change in pH for the top 4-6" of soil for lime ground finer than 60 mesh. 60 mesh or 300 mesh, they both will take the same amount of time (a year or two).

Calcitic lime, CaCO3 and Dolomitic lime, CaMg(CO3)2 are the most common forms of lime used for soil application. Other forms exist and can be used (although not advised). An example would be Quick lime, CaO, also known as Hot lime and for good reason, it is very caustic.

CCE is a rating system based on the acid neutralizing effect of pure CaCO3, with pure CaCO# rated at 100. The limestone from most quarries contain some percentage of impurities so they are going to have a lower CCE rating than pure CaCO3. So a pound of 80 CCE lime will only neutralize 80% of the acid that a 100 CCE will neutralize (this has no relationship with how fine it's ground)

Dolomitic lime will often have a higher CCE than Calcitic lime because Mg weighs less than Ca. A pound of Dolomitic will contain more molecules (more CO3) than a pound of Calcitic lime. (Caveat: dolomitic is slower to react chemically). Calcium oxide can have a CCE over 160 and reacts quickly to change pH, but due to its caustic nature, it can severely damage plants.

FYI, Beware: Pennington Fast acting lime contains some percentage of CaO.

Personally, I don't see the point in Fast Acting limes over a high CCE 60 mesh lime.

The fast acting limes are said to be able to bring pH up in a couple of weeks. Not only is it ground finely, but there is stuff added to make it more soluble than ordinary lime. So for someone with a really low pH, I think it would be helpful to get it up quickly with a fast acting lime and then use the slow lime to work for the next few years to keep the pH from dropping. Here is an interesting discussion on SoluCal. It seems to be intended to get pH up quickly and then used once or twice a year indefinitely at the lower maintenance rate. Read on to the second page of the discussion: if the soil test says you need x amount of lime, you need that amount of lime. Using a fast acting lime does not mean you need less lime. The fast acting lime will raise the pH quicker but you will need to keep applying it year after year to maintain the pH.

Does anyone know what Solu-cal should cost, or if there are different kinds? Amazon and Jet.com have 50lb bags for around $50, one local garden center told me 50 lbs was $25, and another had a sign for $19 for the 50 lb bag.

Go for the least expensive. It should be the same stuff. Maybe Amazon and Jet have built shipping costs into their price. 50 lb is heavy.