Sometimes called 'the friendship sage', Salvia 'Amistad' was discovered at a plant sale in Argentina in 2005 and became commercially available a few years later. It has quickly become a favourite for salvia lovers throughout the world, because of its beautiful rich violet flowers held in very dark bracts - all year round. It is said to be a good compact size at 1.2 m tall - but I have found that it can get taller than this: closer to 2 m. It has lush green leaves. It is similar in flower to Salvia 'Purple Majesty' but blooms for much longer, is a better size and shape, is not too big, and is much less inclined to become straggly.
It prefers to grow in full sun but will enjoy a little protection from hot sun in the afternoons in summer, and will bloom reasonably well in part-shade. It is sensitive to hard frosts. It can be trimmed back every so often through the year, or given a hard prune in mid-August, when it can be given a complete organic fertiliser. It looks effective grown against a backdrop of silver or purple leaves. It can be grown in a large pot. It strikes very easily from cuttings taken in spring, late summer or autumn. Note that this plant is subject to Plant Breeders Rights in Australia so cannot be propagated for sale without the appropriate licensing arrangement.
My plant did not sucker in its early years but started to do so as it got a bit older. In my experience the suckers are fairly close to the main plant. I remove these. It might be an idea to propagate a new one every so often and remove the old one, if you are worried about this possibility. Keep a firm eye on it, anyway!