Various Achillea hybrids including our native Achillea millefolium now come in a range of colours including pinks, salmons, tawny oranges, crimson and reds. The flowers rise up on long stems from mats of feathery cut foliage. Flowering for a long time, the heads often fade to different shades [some fade more gracefully than others]. Some will repeat flower on shorter stems if cut back after first flowering.

I have planted 'Fanal' [c] a lightish cherry red, 'Faust' [b] a fantastic deep crimson with good fade resistance, 'Christl' [a] maroon and relatively early to flower, 'Marmalade[e]' and 'Feuerland' [d] which do a yellow to tangy orange thing or vice versa to different intensities.

They seem to prefer fairly loose soil as a number 'run' and not too crowded or overshadowed by other plants. I also find that with me that don't stay for long perhaps they don't like the rather compacted clay soil.

Nile lilies are natives of South Africa and colours range from whites through to intense purple blues. Some are evergreen others die down in the autumn. Classics for pots providing later summer colour and drama.

The received wisdom is that they like being crowded and fairly warm and dry, this forces them to flower more prolifically. Didn't work for me with A. campanulatus 'Alba' but I have found these two more willing.Sandringhamis fairly low growing with darkish blue flowers.
Golden Rule has gold lines on the leaves and the heads are similar in size but on longer stems and flowers a paler blue. Both die down in the winter. I also have Purple Cloud which is a vigorous evergreen, it is under partial cover but still gets knocked back by late frosts and has not so far flowered for me.
For more ideas on more unusual plants for containers

A brilliant family generally for attracting bees and butterflies and giving interest from spring right through to the autumn.

This selection shows some August / September flowering alliums:
The fireworks effect of A carinatum album at the back, which also comes in lilac. It has very little foliage.
In the middle with flatter more compact heads are Chinese Chives, A tuberosum, the white of the flowers a little more grey/white. Chinese Chives have a lot more foliage, think a tall and flatter leaved chive in appearance, it can be used in cooking.
At the front is the low growing, pinky purple A angulosum. The foliage is like a very fat flattened chive and sort of swirls around about 5-6 cms off the ground.

A delicate native woodland spring flower, Anenome nemorosa [Nemony, Hvitveis, Smell Smock] likes a soil rich with leafmould. It has long thin nobbly tubers that can snap easily when being moved but re-planted should grow on again. They generally grow to between 4 - 6 inches in height. So far the most reliable flowerer for me is Viridiflora.

The breathtaking cultivars are the bluey hued Allenii and Robinsoniana. I am not too keen on the pinks. Apparently 'Allenii' was raised by a local nurseryman, James Allen in Shepton Mallet, Somerset around the turn of the last century. 'Allenii' has a purple lilac reverse to the petals and darker red stems and leaf tints.The inner petal colour is distinctly darker than 'Robinsoniana'. 'Robinsoniana' is large flowered with a very pale almost white lilac reverse and slightly darker lilac within, quite ethereal and also a strong grower.

Vestal is white but a little fitful in it's appearances, has tight white button rosettes of flower inside an outer ring of normal petals.

Viridiflora is all green as it's name suggests, the petals replaced by leafy bracts. This is more of a curiosity than a 'pretty'. Reminds me of the 'green man' motif sometimes seen carved in churches. This anenome seems to be up and flowering appreciably earlier than the others.

I do like 'Snapdragons', watching pushy bees barging their way into the 'snap' and emerging well dusted with pollen. A.majus is a perennial, native to S.Europe but generally grown as an annual.
'Black Prince' flower colour was slightly variable from seed but mainly in the same range the leaves are purple green to dark purple. 'Defiance' is a rich deep velvet orange and taller growing, the leaves have orange tinted backs.

Growing from seed: the seeds are very small so either don't cover at all and let the post sowing watering anchor them a little in the compost or a very light dusting of compost [if using peat free I tend to find the 'bits' are too big for a light cover]. I sow indoors in March/early April and put in an unheated but covered propagator on a windowsill. Once germinated and with a couple of mature leaves, tease apart the seedlings gently and pot-on. Plant out when large enough to fend for themselves @ 4-6 inches and danger of frost is over [May]. Should grow away and flower until the first frosts of Autumn all other things being equal e.g slugs, rabbits, rain, sun etc.

Arisaema

Arisaema candidissimum

I know very little about these plants, they belong to the Araceae family which includes our native Cuckoo Pint, Lords' and Ladies [Arum maculatum]. Cuckoo Pint has a papery greenish spathe and shiny mottled arrow shaped leaves, in Autumn it reveals itself with bright orange berries as the green spathe drops away. For the less faint hearted there is the Dracunculus [which I have never grown] with it's purple velvet upright spathes and smell of rotting meat - upwind it is a dramatic plant, there was a fantastic specimen at Cotswold Garden Flowers when I visited some years ago.
Arisaema candidissimum
According to Rix and Phillips this is a native of pine woods in Western China. I have had this one for a number of years and it has not increased, perhaps as suggested it needs more moisture during the growing season than it gets in my dry soil. In late June it suddenly appears from nowhere, one minute it's not there and then voilà! The spathe appears first on a short stem and then the furled up point of the leaves starts to manifest itself a few days later. The spathe dies away and the large leaves stay until the Autumn before disappearing into the odd hard 'corm' underground. It is supposed to be pleasantly scented but I haven't really noticed. It's very dainty I think. Late June-July

Arisaema ciliatum

Arisaema ciliatum
I know even less about this one, I bought it a couple of years ago from Bob Brown at Cotswold Garden Flowers. The leaves and the spathes appear together, the leaves are more finely cut than A. candidissimum and give the effect of a parasol over the humbug striped spathe. It is also taller growing. The spathes disappear leaving the leaves to build up energy for next year's appearance. This one has increased and this year has produced 3 spathes at different heights which gives a layered effect.

I have also grown some A.Jacquemontii [a Himalayan native], from seed, after 3 years the tiny 'bulbils' have produced a 4" leaf, no doubt the more patient and attentive gardeners would have had faster results! [Bob Brown notes that this may be an acid soil lover, I have it in ericaceous compost].
A sikokianum - bought from Crûg Farm Plants, my father was most impressed with this birthday present!

Chilterns stock seeds of a number of Arisaemas
Paul Christian has an extensive collection of plants as do Cotswold Garden Flowers.

Asplenium scolopendrium

Astrantias are umbellifers in the same family as Cow Parsley. They are European natives [not the UK]. Normally a very quiet understated sort of plant that helps blend showier perennials together, and also good for naturalistic planting. The 'flower' heads carry-on for a long time.

Margery Fish was a fan of astrantias
"A very interesting and unusual variation of Astrantia major is found in cottage gardens in parts of Gloucestershire. The bracts are pale green, about three times as long as in the normal type, and very shaggy. I have never been able to find any name for this truly decorative flower........."
[from Cottage Garden Flowers, 1961] now it is widely available as Shaggy.

Hadspen Blood as you might expect originated at Hadspen, the bracts are a deep rich purple and it is said to be one of the most intense reds available, there are others, for example, Ruby Wedding. There are also 'pinks' such as Rosea. Sunningdale Variegated has creamy yellow variegation on the leaves, looks good in dappled shade otherwise a bit 'showy'.

Planted in sun or light shade not too dry a soil, astrantias are hardy and perennial. May onwards