Well, with a hard freeze last night my first growing season is behind me. I appreciate all the information folks here shared with me earlier and thought I'd post an update.
I ended up investing in a bed-builder/mulch layer for my 38 HP tractor. It works great. Builds a perfect raised bed. Due to Covid-related delays I wasn't able to obtain the clear plastic mulch in time to solarize this year. But I am now prepared in advance for next year.
I decided to roto-till just enough ground to build beds for each order as it arrived. That worked out well as I didn't have to worry about weeds growing in unplanted beds.
The bed-builder automatically lays drip line down the middle of each row. I then planted my rhizomes on either side of the center, staggered, about 1' between rows and 1' between rhizomes. In most cases I had either five or six rhizomes of each cultivar and separated the different cultivars with a plastic edging material from Home Depot called "Choppers". ('Thanks' to Cathy Egerer at Historic Iris Preservation Society for that tip!)
I ended up hand weeding and was surprised how easy it was and how well it worked. (I thought I'd try hand weeding first, before resorting to chemicals if I couldn't keep up.) What I would do is turn on the drip for 48 hours on four of my twelve 65' rows at a time. My soil is loamy sand. After 48 hours of drip the surface would be completely soaked. I would crawl on my hands and knees down between rows pulling tiny little weeds and grass seedlings when they were just large enough to get hold of. Most of them were less than 1/4" tall, just germinated.
The first two times I weeded there were a lot of seedlings. The third and fourth times there were probably 25% as many, at most. After that I rarely found any new weeds or grass seedlings. And that was without being able to solarize. I was surprised.
At any rate, my iris beds are clean and weed-free. Next year's ground is planted in a cover crop for the winter. I'll turn it under and plant mustard early next Spring, then turn that under, give it time to break down a bit, roto-till and build all my raised beds which will be covered with solarization plastic as I build them.
With the drip line already installed under the plastic I'll be all set to solarize each row until my 2022 rhizomes begin to arrive.
By the way, all the irises I planted this year are looking great. Good growth, good increase and no signs of disease or borers.
Thank you to Everyone here for sharing your insight and experience!
