Salvia x sylvestris is a hybrid species created by crossing Salvia nemorosa with Salvia pratensis. 'Mainacht' forms an upright, branched clump about 24 inches tall and wide. Deep violet blue flower spikes appear in May and June, and then sporadically until frost. The stems are square and the leaves are oblong to lanceolate and aromatic when crushed.
German nurseryman Ernst Pagels introduced Salvia x sylvestris 'Mainacht' in 1956. It has remained one of the most popular cultivated salvias and was awarded the Perennial Plant Association Plant of the Year in 1997. This plant is commonly sold as May Night.