The best known Impatiens must be the 'New Guinea' hybrids, or 'Busy Lizzies' as they are also known. These are available from garden centres and nurseries from early summer onwards. Bred for their huge brightly coloured flowers, it's a shame the 'New Guinea' Impatiens aren't hardy and that they never seem to do as well the second year if they are overwintered. They do, however, have a very long flowering season (from early summer until the cold kills them!) and are very useful container plants and fillers in a border with other bright colours. Only bad point, apart from being tender, is that the flowers can be spoilt by rain- so regular dead heading will keep them in tip-top condition.
I first became aware of the hardier Impatiens on a visit to Crug Farm in North Wales, where I met Impatiens tinctoria. Truth be told this is not the most attractive of plants- it's long bare stems bulge in places, reminding you of knobbly knees (!), and the leaves are dull, mid green and not all that big. The flower, though, is something special; big white petals with tiny red spots. I. tinctoria would make an excellent addition to a shady part of the garden where other plants would disguise it's.... less attractive elements, and where the flowers can be appreciated.
A bit smaller and generally more attractive is I. omeiana which, I believe, is Chinese in origin. The dark leaves are tinted red, and the long golden flowers are held above the plant in mid to late summer. Not the worlds more instantly attractive plant, but a nice thing to grow under shrubs in a woodland setting.
Very similar to the above is I. omeiana form 2, which has very similar flowers in every detail, but has slightly larger and chunkier leaves, and this time the leaves are a grey/green colour with a silver stripe down the middle. Mine has grown very low this year, but that may be because it is underneath a big Rhododendron which I suspect intercepts most of the water. That might also explain why the leaves are looking a bit brown and crispy around the edge! Impatiens omeiana form 2- quite similar to the original I. omeiana, but slightly larger flowers.
There has been a bit of confusion over Impatiens sp. from China. I bought a plant labeled as this, but it turned out to be I. omeiana form 2, but seeing as I didn't have this already I wasn't too bothered! As I understand it, Impatiens sp. from China is more of a branched plant, with smaller flowers. I believe this to be the real Impatiens sp. from China! Part of me thinks this may be a plain green form of Impatiens stenantha (see below).
Also somewhat diminutive is I. stenantha (above). This charming gem has been growing away in the Underpass at the RHS garden at Rosemoor, Devon, for many years; here in the shelter of huge boulders I. stenantha makes a small shrublet of red stems and leaves, occasionally producing a small golden flower. I was fortunate enough to be given permission to collect a small piece of this plant and it is now growing away in my collection. Like all of these smaller Impatiens it seems to dislike drying out too much and seems to scorch a bit in excessive sunlight.
There has recently been increased interest in Impatiens species, with many new species being introduced from the wild. One of my favorites at the moment is I. puberula HWJK 2063 (below). Collected in Nepal by Dan Hinkley and Bleddyn and Sue Wynn-Jones in 2002 this mauve flowered gem is really developing into a nice clump in my shaded garden. The plant itself has an almost shrubby habit, a bit like that of I. stenantha but is generally a chunkier plant (bigger leaves, thicker stems etc). So far it has grown well here, taking cold winters and reappearing in spring with renewed vigour. The flowers are quite big for the genus... or at least what I've seen of it so far!
Until recently I was happy to say that this Impatiens was blue. That is, of course, until I met the gem-like true blue flowers of I. namchabarwensis! This bafflingly named species, from a remote gorge in Nepal, is so distinctive that I felt the urge to grow it, even though it is not really all that hardy. So far though I have not had it long enough to see if it has any bad habits!
Most of the species I grow or have seen have similarly shaped flowers, so when I saw I. polineae BSWJ 9722 (below) I was amazed by how it seems to differ. Being quite small in stature it would make a very nice addition to any partly shaded area, and it would probably associate very well with other plants. I have yet to try this for hardiness, and am protecting my solitary plant of it in the greenhouse for this winter; after all this species was collected in southern Vietnam!
The height of these hardy Impatiens seems to depend on how much water they are getting. If they dry out too much they may only make plants a few inches tall, but under ideal situations all four of the ground cover species mentioned here could easily make 1ft (30cm), but I doubt they would make more. Their spread seems to be indefinate, but they are shallow rooted and are easy to pull up if they become a nuisance. I. tinctoria is obviously a taller grower, but again height depends on moisture levels. I. tinctoria just seems to make a tight clump of stems, and slowly expands outwards. Be careful if you need to move it- the woody root system will break easily, so cut the top growth off, or move it in spring before the growth really gets going. I. cristata may grow taller than the plant I saw (which was under trees in a woodland garden, and probably not watered), and produces stems with some distance between them! However it's owner claims it is not all that invasive.
Sometimes of course it is worth growing something less than hardy in the garden if it is a good plant. This is why I maintain a supply of Impatiens kilimanjaro x pseudoviola. The bright pink flowers on a spreading frame make excellent fillers in the garden, especially if used with other brightly coloured plants.