Have a professional soil test done. They will tell you how much lime to add if it's needed.

Rodney

You can get one done at your local agricultural center. It will also tell you the levels of your other nutrients. It costs about 7 dollars here.

The native soil here is quite acidic, but adding organic matter, compost and composted manure moves the pH toward neutral. I keep a couple of beds more acidic than others by amending with rotted sawdust -- those beds grow phenomenal potatoes. All the beds get a liberal sprinkling of wood ashes twice through the winter months. Used off season, wood ashes make a good substitute for lime. Mind you, I use only organic fertilizers, so I don't have to factor in acidification and salts from synthetic fertilizers.

Don't guess... soil test! That was drilled into our heads during classes. Too much lime is as bad as not enough and it's really difficult to judge without a professional test. And the test needs to be repeated every three to five years because soil conditions change over time. Rain often increases the acidity and crop residue and other additives can alter it one way or another. It's not a "once and done" thing.

Because you've added manure, you might want to wait a couple of months before getting the soil sample for testing. That will give it time to break down in the soil and the test will be more accurate.

Sandy

The key question here is whether your soil is acidic or alkaline. You probably know that already, just by asking around. Are you growing hydrangeas or blueberries? I don't. Where I live, the soil and water are both slightly alkaline, as we're sitting on top of limestone. Yep, pretty much the same lime.

The main purpose of lime is to reduce acidity, so if you know your soil is alkaline, don't even bother getting a soil test to tell you that, and don't even think of applying lime.

I had a soil test done which showed I was quite low in calcium. I knew this was the case regionally and I had already been adding lime, but not enough. I had to add an additional 200 pounds on my 1300 square foot veg garden. Some things grew much better than they had previously.
The test also showed I was very high in phosphorous so I have stopped adding that. I plan on a soil test each and every year going forward.

People around here hear they should add lime to their yards and gardens and believe it. We have an average ph of 7.5 but they don't know any better. I was at the farm store one day when a guy was buying lime. He asked the employee how much he needed and the employee gave him an answer. I had to speak up. How do you know how much is needed without knowing the ph? I explained it and the man and employee both looked at me like a stupid girl. The farm store thinks you put gypsum on to lower ph. So they sell lime and gypsum, neither of which is needed here, and refuse to sell, or order for me, sulfur, which is very needed here. I have found it elsewhere.

A handy rule I learned from an ag extension office is ...

Add a few drops of vinegar to a tablespoon of dry garden soil. If it fizzes, your soil's pH is greater than 7.5.

Add a pinch of baking soda to a tablespoon of moist soil. If it fizzes, your soil's pH is less than 5.0.

Of course, you can just pay a few bucks for some pH paper and do it right.

I know down here Time to Lime is a popular advertising slogan. I'm a master gardener. We always advice a soil test first. I don't remember one test ever coming back with the need to lime.

Here in the Boston area, our soil is naturally acidic - due to bedrock, rainfall, etc - so I know I can put dolomite lime on the garden and lawn every year and do good things. I just put it down on my cleaned beds for next year, as it needs time to bread down and become bioactive. It's also a good source of calcium, so I kill two birds with one stone.

I always leave the lime out of the bed I'll be using for potatoes next year. If not for the certainty I have about my soil, I would definitely get my soil tested.

Yes, it pays to know what kind of bedrock is under you. In areas with limestone bedrock, alkaline soils are pretty much the rule. There are several natural ways to acidify soil, but pyrites, which are common in many different kinds of metamorphic bedrocks, degrade into sulfates, which acidify soil.

Our soil (over limestone) is mildly alkaline, and it is largely a losing battle to try to acidify it. That's because the groundwater is similarly alkaline, so irrigation (which we have to do a LOT of) just kills the acidification you're trying to achieve. Yeah, collecting rainwater would be best, but we just don't get enough.