We have supplied specialist solar seed mixes to over seventy solar farms or parks in the UK, most of which we have seeded too.
These are usually mixes of British native wild flowers and grasses in combination. Seed mixes like this
significantly enhance biodiversity on what was typically agricultural land, and are also relatively easy and cheap to manage. This is particularly true if the sites are grazed through the winter.
Solar seed mixes are also - in our experience - surprisingly easy to establish. The sites we're working on are usually low grade land, so competition from aggressive weeds is less than you might think. In any case, starved of chemical enhancement, "fertile" soils often become infertile very quickly!
The caveat to these comments on ease of management and establishment is that is that weed management has to be done promptly and pro-actively. We sometimes find that neither budget nor management system allows for this.
Solar site in Hampshire, 6 months after seeding, poor calcareous soil. Freakishly good result, using local direct harvest mix.
There is absolutely no "one size fits all" approach, as you might think if you read the blurb on some suppliers' websites. There's a whole range of options, to fit budget and site specifics. We work with ecologists and developers to come up with an ecologically appropriate solution specific to an individual site, which won't break the bank.
There are some guidelines which we follow, however.
1. Always, always use seed with documented UK provenance.
2. Always, always use wild species, not agricultural cultivars. Cultivars of wild flowers, like Bird's foot trefoil, don't last very long and don't benefit wildlife to the same degree that the wild plants do. "Wild flower" and grass cultivars grow much faster and much bigger; they will need a lot more cutting. Buying seed mixes consisting of agricultural cultivars is a false economy.
3. If possible, use a direct harvest seed mix with local provenance. This will be more appropriate, produce better results, and - frankly - look good in terms of corporate PR. These mixes are also typically great value for money, given their high floristic content.
4. Don't be tempted to seed at less than 30kg/Ha - 40kg is ideal. There are some folk who recommend seeding down to 20kg. This won't give you a reliable result.
5. Always find an experienced seeding contractor (like one of ours!). Sowing wild flower seed is a very different thing to drilling wheat.
6. Try to use a minimum of 80:20 grasses to wild flowers, if your budget allows. Sometimes specifications are 90:10 or even less, which mixes are cheaper but much less effective.
7. Don't be tempted to use commercial "bird seed" mixes. These look cheap, but have limited value to invertebrates and require regular reseeding. A traditional wild flower meadow mix will not.
8. Look at the design of the site. The width of the arrays themselves as well as the alleys between them can dictate the solar seed mixes which will work best.
9. Manage expectations. Wild flower meadows aren't built in a day. The longer they take to establish the more diverse they can end up.
10. Try to ensure the site operator follows an appropriate management regime.
Site in Oxfordshire, 18 months after seeding. Difficult, heavy soil.