Why aren't my potatoes softer after cooking in a slow cooker for 5+ hours?!

My answer will probably be deleted but I don't care, the answer from JQuick made me angry. You know, that long rant? How dare she (he?) say that slow cookers are for 'slow people'? Or that they're just 'buffet warmers' and 'not to be used for cooking'? What a jerk! I have to retort and say "YES THEY ARE FOR COOKING!' DUH! If it weren't for Crock Pots I would have gone crazy back in the days when I was still able to work. I'd put dinner on before I left for work and it'd be ready when I got home. Super easy! They are great for cooking roasts, chickens, stews, so many things. No one has the right to come on here and speak down to those of us who 'choose' to use Crock Pots.

As for why your potatoes (which have given me a massive craving!) are not soft I have no idea. I know that there have been times when I've cooked a roast with veggies and have tossed chunked russet potatoes in the pot (under the roast), the carrots cook soft as well as everything else but once in a blue moon the potatoes ar still hard as rocks. Drives me nuts to no end! Other times they can cook too soft. Why? I have no idea! Good luck figuring this out, maybe in the meantime you should just bake them in the oven?

BTW, I'm quite sure you knew which was 'warm' and which was 'low'.

30 years cooking experience behind me.

This sounds vaguely familiar for me too. As I recall, it happened with a cheap slow cooker, like one of those $14 Walmart specials. I remember some of the potatoes being soft, like the ones on the outside and the inner potatoes still being crunchy.
I have a really nice All-Clad after being through a lot of cheapos. It cooks everything perfectly, however I haven't tried the scalloped potatoes in it. I don't think it's your recipe since most of them are pretty basic.

It sounds to me like you are slicing your potatoes too thick, try slicing them thinner. I do scalloped potatoes in my slow cooker often and as long as they are sliced thin enough they turn out fine, also make sure there is enough liquid to cover them completely

What are the recipes? Is your slow cooker working properly? Some slow cooker's 'Low' setting is for keeping food warm, and it's not hot enough to actually cook. Maybe you should try a higher setting?

You might want to get a new slow cooker. I can't imagine that potatoes cooked overnight would be anything less than mush.

hard to say without seeing the recipe
was there enough liquid in the cooker?
or the recipe?

Why would anyone want to attempt any recipe for scalloped potatoes that's measured in hours?

It takes 20 minutes at most to cook the potatoes to tender in a sauce pan, and less than 6 minutes in a pressure cooker. I'd probably be done eating my scalloped potatoes, by the time you get your slow cooker out and ready. Slow cooking is for "slow" people. Slow cookers shouldn't be used for cooking - they are electric buffet warmers, good for keeping food hot for serving. Buy a pressure cooker. Get your life back. 8 hours for potatoes, sheeze, what a massive waste of time. I could be ready to serve the entire crew of an aircraft carrier all the scalloped potatoes they could eat in about 30 minutes, at least after the potatoes had been peeled, sliced, and kept in water. I could cook the potatoes faster than they could be served. 8 hours?!? Really now. These are potatoes.

But in direct answer to your question, the problem is the cooking temperature. The starches in the potato are not reaching a high enough temperature. This is called starch gelatinization, and your slow cooker is not reaching that temp, or the potatoes would be cooked in 20 minutes or less, probably much less than that, since you said you're slicing them very thinly. That brings up the second problem - if your slow cooker was hot enough (and it certainly isn't) then cooking the potatoes longer than their gelatinization requires will cause them to break up, and liquify in a matter of minutes, much less hours. The starch in the potato is as accurate as a thermometer for judging the temp. I'll guarantee that if you measure the cooking temp with an accurate thermometer, the slow cooker will not be reaching the gelatinization point of the potato starch.

Cateyes, you prove my point. How can you have 30 years of cooking experience yet not know why potatoes don't get softened? I just explained why, hon. Can'tcha read what I be sayin'. I'll slow down for ya. Slow cookers are just right for you. Perfect, in fact. You keep doing your potatoes in hours while the rest of us do them in minutes. A pressure cooker would be much too advanced for you. Everything you like doing in a slow cooker can be done in less than an hour in a pressure cooker, with better results, using fraction of the energy.

Oh, about 30+ years of experience cooking potatoes. I'm a friggen potato cooking expert. I can cook them faster than you can read this page.