Depends on how big the rocks are. but if they're not big go ahead and plant. Lava rock is porous. The soil should be loosened especially if it's clay--you didn't say what your soil is, but clay should also be amended

If there's rocks you can't rototill--not good for the tiller. I use the garden claw on mine but you have to have loam for it. The tines simply don't go into clay.

Take it easy buying Stella De Oro. They grow fast and need dividing often. Better to buy a few and fill in with annuals or perennials for a few years. Don't get me wrong I love mine, but once they are established like mine are it is almost a yearly thing to divide them. You might want to check out Brown-eyed Stella and some of the other everblooming daylilies too

Congrats on having finished the horrible rock-removal project. You are to be commended for having rid the world of so much noxious rock and plastic!

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Happy Returns is a yellow version of Stella (I'd call it lightish lemon).

Rosy Returns is the pink version.

I believe oilpainter's Brown-eyed Stella is actually Black Eyed Stella. Mine doesn't bloom as much as my Stella De Oro or Happy Returns, but the size is much the same.

You can search all three in this database and find pictures as well as basic information. [Unfortunately, I cannot link to specific pages.]
http://db.tinkersgardens.com/

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This site lists other everblooming daylilies of the Stella line. I have never purchased from them and have no idea if they're a good vendor or not:
http://www.perennials.com/hea.html

I recommend you visit the Daylily forum and ask advice there about individual cultivars and vendors. But I warn you: it's an addiction.

All of those little critters are signs of a healthy garden.

I would leave the lava rocks and spade turn them, along with organic matter amendments, into the soil if you don't wanto to roto-till. I grow stellas along my road in a nearly 50% road base and soil mix, and they do fine.

Stella's are nice for early bloom, but for mid-season blooms look at later blooming varieties as Oilpainter suggested.

isabella, you may be thinking of a different variety.

Stella De Oro and the others in that family bloom pretty much continuously. They have both rebloom (multiple bloom periods per year) and extended bloom (extra-long bloom periods). The combination (everblooming) is unusual enough that people are willing to put up with relatively small flowers, limited color choice, an old-fashioned flower shape compared with more modern cultivars, and shorter scapes (flower stalks).

Stella's may be the best everbloomers to date, but even that trait is not reliable in all zones, especially the colder ones. Often the re-bloom is sparse and not worth waiting for. Typically in Zone 5-6, the Stellas first flush of blooms has peaked by mid-July. It may come back later in the year, but not nearly with the same vigor.

For more daylily color with real vigor, planting another variety would be a better guarantee of color. Check with your regional gardening forum, as gardners in Michigan will have more first hand advice.

For some really great daylily choices check out the Tranquil Lake Nursery website. I visited the nursery this weekend, during the mid-season bloom, and it was spectacular!

Another consideration would be to plant some rounded plant forms to contrast with the spikey forms of the daylilies.

Thanks for the input. We put down the mulch yesterday and I just like it so much better than those rocks.

Funny enough, I put an ad on Craiglist -- Free Lava Rocks -- I had 30 people that wanted them! All 20-some bags were gone the next day. I would have paid them to take them -- they were very heavy and taking up half my garage.

For some reason those things can be hard to come by. I only use them for my gas BBQ. I went to the store a few years ago to buy some, and I was told they were no longer carried. Interestingly enough or unbelievably I was told they were not carried anymore because the pores supposedly harbor bacteria. Maybe it's a unfounded rumor.