Alchemilla mollis, common name Lady's mantle, is an easy to grow herbaceous perennial, fully hardy and which will grow successfully in many conditions. The preferred growing conditions for Alchemilla is damp soil with some sun, but it is a vigorous plant which will survive in most conditions. This means it will tolerate semi shade, any aspect, exposed and sheltered spots which makes it a useful plant for awkward areas. It will also grow in damp areas as long as they are not boggy. The most common variety on sale is A.mollis, a good variety with the RHS award of garden merit, always a safe bet when choosing a plant.
When it first comes into leaf and Alchemilla makes a fresh mound of zingy lime green foliage which is very attractive, especially with raindrops as seen in the image. The leaves are almost downy in appearance and hold the water well.
Alchemilla mollis is one of those plants, like Hostas, which look good in the rain. Flowers are formed on sprays, with multiple flower heads. When the flowers first emerge, they are a strong lime green colour which becomes a mass of tiny yellow flowers from early summer onwards. This variety grows to around 60cmc and makes good at the front of borders.
Alchemilla mollis looks good with many plants, especially good with Allium cristophii and the lime green foliage looks good with purples and blues. One advantage of growing Alchemilla with Alliums, and why it's such a good companion plant for Alliums, is that often the leaves around the base of Allium look tatty even before the plant has flowered, it's one of its shortcomings. Plant Alchemilla around the Alliums and it will cover the base leaves of the Allium.
Alchemilla also looks good as a contrast growing around the base of a Cotinus "Royal Purple", the strong lime green contrasts with the purple. The contrast is good but to be aware a Cotinus is potentially a large shrub, 3 meters plus, although it can be kept in check by pruning. Alchemilla also look good combined with the soft blue of Nepeta (Cat Mint) a nice mix of blue with lime green/yellow and both flowering in June.
I have also seen Alchemilla planted to good effect growing at the base of a copper beech hedge and Alchemilla looks good along a path.