Improving disturbed gravel soil

I'm new to this community, but not to permaculture and thank you in advance for your advice and feedback! We're currently building a house on five acres outside of Kalispell, Montana and the soil isn't just rocky, it's all rock! No real soil to speak of. While I want to give it a year or so before I dig into the overall plan, the septic drain field is being installed in a few weeks which occurs to me has both its benefits and drawbacks.

It's going into a large flat area that is the main view from the house and, since it's the drain field, I'm thinking it would make a nice native wildflower meadow since we can't put food producing plants there.

So, we have the opportunity while the soil is disturbed to do...something. If we don't, we'll likely get a bunch of oxeye daisy and knapweed germinating due to the disturbed soil, which is incredibly invasive here and will have to be dealt with later. But I'm afraid that simply adding compost or topsoil will just get washed away through the well draining gravel in the coming year and I'm not finding a ton of info online (other than one other thread here about reclaiming a gravel pit) about how people have dealt with this.

Any thoughts? Perhaps a layer of heavier mulch like wood chips and straw to suppress the weeds before adding compost to germinate wildflower seeds in the fall? The attached photo isn't the exact location but is indicative of the soil on most of the property.

I have been part of a monitoring group on a project to restore species-rich grassland on an ex-limestone quarry site.  We have a very species rich field, nationally designated, which is going to have to be quarried, so the quarry company have been required to trial methods in order to ascertain the best chance of success.  At no point has adding compost or other rotted matter been part of the methodology.  Granted on some of the plots they have been taking topsoil in the form of whole or mashed up turves from donor sites.  But on other plots they have been spreading plant material (freshly cut hay and/or harvested seed) straight onto bare fractured rock or scalpings (basically gravel).  After a few years it has got to the point where the vegetation has developed enough to be able to introduce sheep grazing.  The interesting thing is that in the beginning there were clear differences across the plots, but things have evened out now to the point that they are all performing more or less the same.

So if I was looking at your site, I would be looking for a nearby meadow with the right kind of wildflowers in, and mowing it at the point where the seed is almost ripe (in this part of the world this means mid-July onwards), transferring it straight onto the recipient site and spreading with a much spreader or similar.  We usually reckon on 1 hectare of donor site being sufficient to innoculate 2 ha of recipient.  If you add a thick layer, if possible turn (ted) it to ensure even drying and for the seeds to drop out.  You can then turn stock in to eat, distribute and trample in the seeds.  This is a method we use routinely to restore species rich meadows.  Usually we are prescribing to disturb the soil first to create bare ground, but it seems your situation will not require this.

Hope this may be helpful.

The point is that "wildflower meadows", at least the ones I deal with, are a human-created habitat with depleted fertility, which is how the wildflowers can compete with the grasses.  On soils which are high in phosphate due to intensive applications of manure and fertiliser, introducing wildflowers is doomed to failure.  We always ask for soil tests first and if the phosphate is too high, we won't fund restoration.

Plants actually don't need soil in order for them to grow, roots like air and only need something to anchor in, that is why hydroponics and aquaponics work.
In hydroponics you can use rock wool as the root support medium or gravel. Same goes for where you are.
Getting some organic material growing in those rocks is the way mother nature would do it so why not use her methods?

Redhawk

Thank you for the thoughtful feedback! It's actually a great point that wildflowers don't need good soil as they are often the pioneers in a disturbed site anyway. I really like the idea of transferring material from a cut wildflower field to the property although I'm not sure I have access to the land and materials I would need to do that. I'm thinking my best bet considering the fact that the soil is going to be turned over in the next week is to secure a native wildflower seed mixture to broadcast over the area and see if I can get ahead of the invasives! Thanks so much....

I'd think that the extra nitrogen and water from the leach field would make native wildflowers unsuited; they will probably be outcompeted by various "weeds."