You can but it is recommended that you have a rack over the bottom jars to disperse the weight of the jar/jars on top. Anything similar to the one on the bottom to keep the jars off the bottom. Hope this helps. And of course at least an inch of water over the top jars.
I have a recipe that calls for 4 heads of dill. If I don't have that, and my store doesn't sell that can I substitute dill seed and sprigs instead of the 4 heads of dill?