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Sharp Gardeningby Christophe Holliday
Once you have created a structure of sharp foliage and spiky accents, it's time to decorate.
For some gardeners the plant shapes and foliage of swords, lances and spiky rosettes are enough, and for a low-maintenance garden with few flowers this look is hard to beat; but most gardeners are keen to incorporate flowers into their planting schemes. Flowers are the lifeblood of the garden. After all, they open up so many different seasonal excitements, from the anticipation of emerging buds to fleeting blossom, followed by autumnal seedheads, and finally winter skeletons. Butterflies and insects are part and parcel too, as are birds foraging in them for insects and the food from seedheads. All this creates life and movement, without which no garden is complete; sterility is kept at bay. If nothing else, gardens are about reproduction.
When designing with perennials, it's important to get the backbone right first; I would not plant perennials first and spiky evergreens afterwards. Establish a framework of spiky plants first. Follow this up by adding flowering plants as ornamentals. Just as an artist sketches out the bare bones of the painting first, before adding colours and hues, follow the initial structural planting with bulbs and perennials whose dominant characteristic is flowers, and which complement the colours and textures.
Ignore traditional herbaceous flowers. Perennials such as hostas or hardy geraniums look out of place next to the more hard-living and rugged spiky plants. They may also do damage. Most of the lance-shaped plants and spiky rosettes need to have air circulating around their necks, especially in winter. Perennials with lush foliage, which create a thick eiderdown of leaves, will have a detrimental effect, especially from autumn onwards when the leaves are reduced to a soggy pulp. In summer their foliage will create undesirable shade close to the swords and spikes.
There are other homes for these plants. Besides, their required growing conditions are incompatible. Whereas many herbaceous perennials hibernate and are impervious to winter wet if they are fully or frost hardy, and are happy in moist semi-shade, most sharp foliage plants need sharp drainage, preferring a warm, sunny, well-drained spot. A yucca will not take kindly to a wet winter without good drainage, and may well rot off and even die.
Instead of planting herbaceous perennials, dramatize with spiny flowers, especially those that are prickly to the touch. Ignite with sky-piercing spires that echo the giant blooms of succulents. Finally splash in some contrast with chunky-headed globe flowers whose strap-like leaves echo sharp architectural foliage. By keeping to a smaller palate of perennials with bristling flowers and jagged foliage you will be well on the way to creating the sharp garden look. Narrow the field to those that look appropriate with sword-like foliage, and then have fun playing around with various combinations.
There are three main flower types that fit in with this theme. Barbed, prickly thistle-type flowers such as eryngiums look sharp and are sharp. Tall spires, such as kniphofias, echiums and eremurus, echo the jagged shapes of spiky evergreens. They act as exclamations and have an appealing punchiness. Globe flowers with strappy leaves, such as alliums and agapanthus, rest the eye, acting as full stops. The long narrow leaves are supporting players to lance-shaped foliage. Many of the ones selected here flower from mid to late summer, some well into autumn, so they are valuable for keeping the garden going throughout those late months.
Whereas the foliage on spiky succulents is usually of primary interest, and the flowers are subordinate, most of the leaves on these perennials are subordinate to the flowers and usually echo architectural foliage. Some plants begin life with strap-like leaves, which echo larger lances and swords, but die off leaving the flower as the star attraction, such as alliums.
If you look at the flowers of many spiky leaved perennials or better still, touch them gently, you will find that there are hundreds of miniature prickles on each flowerhead. These thistles are low maintenance because they love poor, well-drained soil and full sun, so no lugging and spreading of compost is required. Their survival is threatened by excessive winter wet and shade.
The cardoon thistle, Cynara cardunculus, from the Mediterranean and Morocco, is a statuesque perennial, with silver acanthus like leaves, 50cm/20in long. Looking resplendent in late spring and early summer, its leaves look good enough to eat. You could remove the budding stems if you wanted to enjoy the foliage alone, but it seems a pity to miss its 1.5m/5ft flowering stems with hard spiny flowers topped with a peacock's purple crown. These thistle tips are soft to the touch, like shaving brushes, but beware the spiny barbs that guard them. This sun-loving thistle is best grown out of strong winds, to stop it toppling over, and to perform best needs well-drained fertile soil.
Tall perennials such as Cynara cardunculus are plants for the main border. The evergreen silvery foliage starts growing early in spring and is attractive throughout the season. The length and fleshiness of the foliage mean that it may smother a plant that needs plenty of air around it, which you do not want. Although a young plant does not want to be suffocated, once phormiums are established they are less fussy about this. So plant it near a Phormium tenax, where the grey-green of the phormium's foliage is highlighted by the silvery grey cardoon leaves. The size and stature of both perennials are in keeping with each other. You could also place Cynara cardunculus in the middle or behind some of the Phormium cookianum hybrids. As both have arching leaves they look elegant together.
A very similar-looking thistle is the biennial Onopordum acanthium from the Mediterranean, Europe and western Asia. Its grey woolly leaves are spiny-toothed, and at first glance there is not much to distinguish it from the cardoon. How do you tell the difference between the two? Whereas the cardoon flowers on tall stems emerging from the base, the onopordum has side shoots, throwing out from the main stem flowering stems with bright purple thistles. It can reach 2.5m/8ft, in its second and final season. The cardoon is more stately than the onopordum. The onopordum is something of an upstart, self-seeding easily. This can be a curse, but it's easy enough to hoe the seedlings out. Its ability to self-seed makes it a good plant for planting in gravel. If it lands near the front of a border, leave it, because you can look through the freely branching stems to plants behind it. This is a good way of creating perspective.
While the cardoon takes time to settle down, sometimes not flowering until its third season, the biennial onopordum provides flowers within a couple of seasons, so if you are in a hurry you could plant some onopordums while awaiting developments from the cardoons. As with most silvery-leaved plants, onopordum enjoys poor soil and full sun — its preferred habitat is a stony slope. Bear in mind that it needs to be in a border at least 2m/7ft deep so as not to look out of proportion. Bees love onopordum flowers. Once flowering is over the heads turn to cotton down — a reminder that the plant is also called cotton thistle. Its brief life and roving nature add excitement to the garden, for no border will be quite the same the following year, as the onopordums die and settle elsewhere.
Another biennial thistle, Silybum marianum (Blessed Mary's thistle), grows to about 1.5m/5ft. Living hard on stony slopes in south-western Europe and north Africa, it prefers full sun and poor, well-drained soil (neutral to slightly alkaline), which help it survive winter wet, although it is fully hardy. With its exaggerated elongated bracts, surrounding purple-pink flowers, it resembles a cartoon version of the cardoon. The foliage is glorious. Marbled with white veins, the glossy dark green leaves are deeply lobed and spiny. Some gardeners remove the flowers to retain silybums as foliage plants. Incredibly the unpalatable-looking leaves prove delectable to slugs and snails.
Further members of the thistle family include echinops, which reaches 9ocm/3ft in height, thriving in dry grassland and sunny gravelly slopes from Europe to Asia, India and the mountainous regions of tropical Africa. Its spiny foliage is grey with white undersides. The globe thistle flowers are a perfect sphere of blue pin-pricks, the colour lasting for several weeks. If you don't cut down the stems in winter you will encourage bullfinches into the garden, hungry for the seeds. Echinops will self-seed if not dead-headed. Look out for the late summer blooms of Echinops ritro 'Veitch's Blue', which is a deeper blue than most.
Not only do echinops' pompon flowers contrast well with their leaves, but the spheres make a useful foil for any sword-like foliage. Because they clump up vigorously after three years, it is best to keep them in check by dividing them every couple of years or so, before they encroach on the evergreen leaves of spiky plants. They love poor soil in full sun, and will still flower in partial shade.
Eryngiums are thistles with attitude. Everything about them looks hostile and uninviting. Barbs, spines and prickles sharpen every leaf, bract and flower. Their armoury discourages nibbling herbivores in their native rocky, coastal habitats of Europe, Africa, Asia and China. But in spite of all their repellent protection, they are plants of great beauty. Their umbel flowers are held among the bracts like diamonds in a ring.
Nevertheless, you are unlikely to forget an encounter with a sea holly (E. maritimum) if you accidentally stumble upon one barefoot in a sand dune on a seaside holiday. Each leaf is a mass of thorns ready to trap the unwary and the hard, steely flowers are just as antisocial. The thimble flowers within the bracts are as sharp to the touch as the leaves, but it is the prickly bracts surrounding them that discourage any potential munching predators. Looking so spiny, it is easy to imagine that these prickly flowers have emerged from the dagger-like foliage of yuccas as if they are yucca flowers themselves. With both plants requiring the same dry well-drained conditions and full sun, they certainly make good companions.
Confusingly, while many eryngiums prefer these hard growing conditions, others like moist, well-drained and fertile soil, still in full sun. The Argentinian frost-hardy E. agavifolium is one such plant, the flowers of which resemble giant thimbles set in small bracts. They lack the blue steeliness of most eryngiums, and are best described as greenish white flowers 5cm/2in long. Reaching well over lm/39in tall, they stand up well without staking. They come into their own when they turn a deep dark brown lasting all winter — looking much better like this than when flowering in summer. The reference to agaves in their name describes the leaves, which are highly sharp-toothed swords.
There is an eryngium for every location: ranging from gigantic to dwarf there are over 200 species. Here is a handful. Unless otherwise indicated you are safe planting the following in full sun, on poor, dry, well-drained soil.
E. bourgatii, found in the Spanish Pyrenees, bears branching stems with masses of small grey-green flowers, amid star-like silvery blue bracts. The blue stems grow to about 45cm/l8in tall. Twice as high, Mediterranean E. × tripartitum has violet-blue flowers with blue-grey lance-shaped bracts. A good eryngium for a raised bed or rock garden, where the soil does not get too dry, is the Moroccan E. variifolium, which reaches 30cm/l2in. The silvery white bracts are narrow and pointed, the flower pale blue.
E. giganteum or Miss Willmott's Ghost is an essential biennial, or short-lived perennial, found growing from the Caucasus to Iran. Its highly veined pale green bracts turn to silvery grey and encase steely blue flowers. The whole plant is about 90cm/3ft tall with a spread of 30cm/l2in, and seems to look better with age. 'Silver Ghost' is smaller, and more silvery white.
Of particular interest to the sharp gardener are two slightly more tender species: the frost-hardy E. pandanifolium, found from Brazil to Argentina, which likes moister, more fertile conditions, and Mexican E. proteiflorum. The first should appeal because of its 1-2m/3-7ft-long sword-shaped leaves. The flowering stems can reach 4m/13ft — a magnificent sight. The flowers are less distinguished — a purplish brown — but the leaf and height are outstanding. E. proteiflorum has the finest flowers of all, resembling the flowers of protea, the much loved South African shrub from which it takes its name. The leaves are spinily margined and the whole plant reaches 90cm/3ft tall.
The prickly common teasel, Dipsacus fullonum, from Europe and Asia, is a useful biennial self-seeder in a new garden, until you become tired of it or your garden has filled out sufficiently. It is almost too successful a colonizer: scattering its progeny liberally, it becomes a weed in a few seasons. However, it is useful in an informal area, adding height in the second season as it rises to almost 2m/7ft itself The airy, sparsely branched habit adds a lightness of touch among heavier, strappier foliage. Bristling purple thistle-like cones encased in rigid, spiny bracts wave above thorny stems. It can be preserved indefinitely if harvested for drying indoors. Alternatively leave it outside, where its ghostly silhouette will look good all winter, especially if rimed with frost.
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