My coffee ground like to go moldy inside if it's been a few days. I don't know if I'd want to grow seeds in just coffee grounds, for fear the constant wet would get the coffee ground molding.
There's a
thread somewhere on here where Dale talks about how coffe grounds actually have neutral PH...I'll see if I can locate it.... Ah-ha!
https://permies.com/t/41259/Dollar-coffee-grounds#325051
They're supposed to be pretty neutral. The acid comes out in the drink. I've never tested for PH. I'm told that everything here is horribly acidic, but when I plant stuff, I have to jump back to avoid being hit by the emerging growth.
I use my coffee grounds as a mulch in my garden beds. It kind of repels slugs and bunnies...if it's fresh. Once it's been rained on, it's not very repellent. But, I like how it covers the soil and helps it warm up. I haven't really encountered mine forming much of a crust, but then, mines never more than 1/2 inch thick and it rains here, often washing the grounds into the soil or off of the soil. I love using coffee grounds in my beds, as pretty much any other mulch I use here either (A) breeds slugs (I'm talking about you, leaves!), or (B) is duck bedding and there's a risk of listeria/salmonella. So, coffee grounds are the perfect mulch for my situation. (For the longest time, I couldn't get a compost pile to work, because animals kept eating it. I had one bin broken apart by something that wanted into it's contents. But, now I've got some spiffy tumbling compost bins that were free, and my husband drinks TONS of mint tea for his crohn's. The mint repels most everything, and the bins make it really easy to have to "piles" going, so I'm acutally composting the bedding for application in my garden. )