This isn't a new question, so forgive the answer. I have worked with seeds to grow herbs for YEARS and by far, the most singular stubborn seed I have dealt with is rosemary seed. I read somewhere once that rosemary seeds have a ratio of about 1-20 for sprouting a plant that can survive. I have had success. But it varies and I haven't been able to repeat it consistently. My SUGGESTION is to read up on it and follow the advice of the experts regarding depth and watering. My contribution is to use LOTS and LOTS of seeds and hope for just a few plants to spring up. I don't worry about planting them close together or even on top of one another, as most of them don't take root anyway, but when I started, I planted like 10 to a large pot and expected something to happen -- and it didn't. Most years, I try to grow my own from seed. About half the time, it works. The other half, I get a young plant at the local nursery. If properly tended, a rosemary plant can survive a Tennessee winter, but that doesn't always happen at my house, so...
This isn't a new question, so forgive the answer. I have worked with seeds to grow herbs for YEARS and by far, the most singular stubborn seed I have dealt with is rosemary seed. I read somewhere once that rosemary seeds have a ratio of about 1-20 for sprouting a plant that can survive. I have had success. But it varies and I haven't been able to repeat it consistently. My SUGGESTION is to read up on it and follow the advice of the experts regarding depth and watering. My contribution is to use LOTS and LOTS of seeds and hope for just a few plants to spring up. I don't worry about planting them close together or even on top of one another, as most of them don't take root anyway, but when I started, I planted like 10 to a large pot and expected something to happen -- and it didn't. Most years, I try to grow my own from seed. About half the time, it works. The other half, I get a young plant at the local nursery. If properly tended, a rosemary plant can survive a Tennessee winter, but that doesn't always happen at my house, so...