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The green roof is still white, but that’s the perfect time to spread prairie seeds. As the snow melts, and the soil freezes and thaws, the seeds get in good contact with the soil, and have the snowmelt moisture to get them started. That’s the idea anyways. So last week I seeded three different areas to different mixes. I mixed the seeds with damp sand for a couple reasons: many of the seeds have fluff attached to them which would make them blow away before landing on the roof, and the damp sand moistens them enough so they land on the ground. The other reason is to provide more volume, which makes it easier to distribute small amounts of seeds evenly over a larger area. 
The first mix is 8 different species that I got from Jeff Straub, who sells his prairie seeds through his small company called Woodland Prairie Specialties. Jeff gets his seed from his own land in Waubun, which is near the White Earth Reservation. Jeff’s land is sandy like ours, and I like supporting the (somewhat) local guy. Many of the things from Jeff are the same things that are growing in HUG’s windmill field, like old-field goldenrod, pussytoes, and prairie cinquefoil, and I’m hoping they will be happy on the roof as well. These are seeded in a 40’ x 80’ rectangle on the main portion of the west end. You can see the sand-seed mixture on top of the snow, encircled by flags.  The second mix is 56 different species from Prairie Moon Nursery in Winona, MN. All of these species are adapted to dry sandy prairies, and many of them have rhizomatous root systems. This means they have mostly horizontal root systems, rather than the deep root systems that so many prairie species have, that would have a difficult time in the 6 inches of soil on the roof. I really appreciated Prairie Moon’s huge selection of species and great detail about the kind of conditions that each species prefers, as well as information like what kind of root system they have in many cases. Due to the sheer number of species I wanted to try, I only bought a small packet of most things, so these are mixed and spread on top of a 20’ x 40’ section of the area where Jeff’s seeds are also spread.
I am hoping that, once established, at least some of these species will be able to withstand the brutal conditions of the roof, without irrigation. In the first year or two, Prairie Moon recommends that we have some irrigation. Otherwise the poor things may get started and then fry before they get their root systems established. I think the drip irrigation that we used in the gardens last summer would be a practical choice for the roof as well. I’m thinking we can irrigate part of the area, and leave some to fend for itself, to see what happens. The third area is seeded with two species of annual native prairie legumes, (meaning they are in the pea family, so fix nitrogen in the soil, and flower and go to seed in one season.) These two species, partridge pea, and rattlebox, (also from Prairie Moon) are found naturally in dry sandy areas. I’m hoping that these will come up and bloom and go to seed without needing irrigation. The section of the roof that these are on, is the square section over the garage door, right as you come onto the west side of the roof. The prairie seeds will have some competition, or perhaps some help, from the weeds that will also come up. Last year we let the roof grow whatever weeds would make it, from the composted yard waste we used as soil. In May 2007 it looked really healthy.  There’s nice selection of edible weeds here: lamb’s quarters, pigweed, purslane, sheep sorrel. By mid-June, however, it looked like we’d sprayed Round-up, but really it was just the lack of rain. Unfortunately I have no pictures of this phase. Later we had more rain and another flush of weeds came up, and some lived long enough to go to seed. These are the skeletons that we see there now, and they are dropping lots of seeds.  If we irrigate, of course, this helps the weeds as well as the prairie seeds, and we may need to do some mowing or weed-whacking to keep the weeds from going to seed. I think that having the weeds growing might be an advantage, though, because they should keep the soil surface from drying and heating up as much. We can also forage our salads from the roof! I plan to monitor closely and document what goes on, so we’ll keep you posted. |
