When we think about choosing plants for their flowers in the garden, we almost always think first about colour. Whole books have been written about using and combining plants with colour in mind. But colour is only one facet of a flower’s characteristics – their shape and form can be equally important.
You may also like
Imagine a British hay meadow in full flower in early summer, with sheets of starry white ox-eye daisies and drifts of airy, goblet-shaped yellow buttercups interspersed with the slender plumes of red-pink sorrel. Colour plays a crucial role in the pictorial effect, but if all the shapes of the flowers of the different species were all the same, then it would be nowhere near as interesting as having a diversity of flower forms.
Exactly the same point could be made about North American tall grass prairie. Having a multitude of different flower forms and shapes adds sparkle and interest that goes beyond the foundational qualities of colour. Thinking about meadows and prairies when we consider flower shape is relevant, because it reminds us why plants have different flower forms in the first place. Evolution has resulted in these different outcomes so that flowers are adapted to attract the pollinators upon which they depend.
While some flowers might attract a wide range of pollinators, others may be so specialised as to only allow one insect or bug to pollinate them. Botanically, this means an almost infinite variety of possibilities, and there’s a whole range of technical and scientific terms to describe the precise differences between them all.
Thankfully, we can simplify things considerably when it comes to considering flower shapes in planting design and limit ourselves to just a few main categories, and variations within them.
Of course, the caveat here is that for some plants, it’s the individual flower that stands out, but for others it’s the group or cluster that makes the impact. But my focus here is on how to think about flower shape in planting design terms, and in that regard, the most useful starting point is to distinguish between broadly vertical and broadly horizontal flower forms.
When we think of upright flower forms, ‘spikes’ of various types immediately come to mind. The individual flowers on a spike may vary hugely between different plants, from the tightly packed spikes of a Veronicastrum, where the individual flowers can barely be distinguished from each other, through to hollyhocks, where each individual flower is extremely apparent. In both cases the overall verticality and collective appearance is the thing.
There is a similar wide variety of horizontal forms, from those of the umbel family, where each flat flowerhead is composed of myriad individual flowers, to others such as echinaceas, which are much like single entities (even though daisy flowers are themselves composed of many individual florets).
In the same way that we think about colour in terms of harmony and contrast, we can match flower forms and shapes in the same way, and just as with colour, the most striking and arresting combinations occur when we aim for contrast.
A favourite matching of mine for sunny dry places is the low-growing mounded Euphorbia characias subsp. characias ‘Humpty Dumpty’ with Salvia nemorosa ‘Caradonna’. There’s a strong colour interaction, but there is also something very satisfying about the dark-purple Salvia spikes with their narrow flowers against the pale-green, relatively horizontal flowerheads and round bracts of the Euphorbia.
While contrast is good, putting too many similar-shaped flowers together can result in a rather unintelligible mass. I love to use lots of plants with vertical flower spikes emerging up out of a base layer of grasses or other lower-growing plants, but it’s important that there’s a variety of flower shapes on those spikes to avoid a monotonous effect. Another combination I use a lot is the bright-red Silene chalcedonica with yellow Achillea filipendulina ‘Gold Plate’. Both plants are a similar size, and both have flat flowerheads, but the relatively large stars of the Silene contrast with the moss-like, highly textural Achillea flowers.
This brings us to a detailed consideration of shapes – are the flowers saucer-shaped? Tubular or bell-shaped? Facing up or hanging down? Starry, rounded, grouped or individual? There are no hard and fast rules about what works and what doesn’t beyond avoiding too much similarity; however, considering combinations of different forms takes us to a much more interesting level of plant selection than thinking of colour alone.
In my own garden, I have used the tall Astilbe chinensis var. taquetii ‘Purpurlanze’ in linear bioswales on both sides of my front garden path. This is such a long-season plant, looking good from the moment the new young orange-tinted shoots appear in the spring, all the way through to the winter seedheads. The flower spikes rise in June and look fantastic in bud for weeks before the individual flowers open in light purple.
It is a supremely upright and vertical flower form, and I mix it with the similarly vertical spikes of purple loosetrife, Lythrum salicaria. Although the flower colours of both plants are virtually the same, the individual flowers are very different – the starry purple loosestrife flowers stand out against the fluffy Astilbe flowers, producing sufficient differentiation. I also mix in yellow Ligularia ‘The Rocket’, creating a harmonious mixing of upright flower forms, but with contrasting colours.
And then there are two additional plants with completely different flower forms, which, as a result, really stand out: the brilliant scarlet Crocosmia ‘Lucifer’ and its almost horizontal racemes of funnel-shaped flowers, which makes a great contrast with the spikes of all the others; and sumptuous, acid-yellow Hemerocallis ‘Whichford’ with huge trumpet-shaped blooms. In this mix, colour plays a strong role, but it’s the flower forms that make it enticing.
Flower shapes: an identification guide
Spike
Blooms with spikes or spire-shaped flowerheads create vertical interest, leading the eye upwards and giving height and a strong structure to a planting scheme. Examples include Veronicastrum virginicum, hardy Salvia, Lythrum, Astilbe, Ligularia, Lysimachia, Vitex agnus-castus, Kniphofia, Delphinium, Lupinus, Liatris, Camassia, Aconitum, Antirrhinum, Eremurus and Agastache.
Umbellifer
Umbellifers have flat-topped or slightly domed, broad, multi-flowered inflorescences, like small umbrellas. They are excellent for pollinators and can be used to bring an ethereal, relaxed quality to a planting. Examples include Achillea, Pimpinella major, Ligusticopsis wallichiana, Chaerophyllum hirsutum, Anthriscus sylvestris (cow parsley), Anethum graveolens (dill), Ammi majus, Ferula and Cenolophium denudatum.
Globe
Spherical flower forms are graphic and architectural, standing out clearly within a planting and bringing a sense of energy and playfulness. Repeated in a border, their round shapes act as punctuation marks that bounce the eye along, and a notable contrast to feathery umbellifers or narrow spires. Examples include Allium, Craspedia globosa, Echinops, Primula denticulata, and pompom and ball dahlias.
In the same way that we think about colour in terms of harmony and contrast, we can match flower forms and shapes in the same way, and just as with colour, the most striking and arresting combinations occur when we aim for contrast
Airy
Airy or wispy plants are perfect fillers for spaces in-between other plants, softening transitions in shape and height and bringing a sense of movement. Many have a semi-transparent look or tall stems that mean you can see through them to other plants, creating depth and an open feel. Examples include Thalictrum, Gypsophila, Dierama, Verbena bonariensis, Valeriana officinalis, Knautia and Crambe.
Trumpet
Trumpet-shaped blooms are big, bold forms that create drama and make for striking accents in
a scheme. This means they will often draw the eye, stand out and become a bit of a focal point
in any bed or border where they are planted. Examples include Narcissus, Hemerocallis (daylily), all Lilium including oriental and martagon, Cobaea scandens, Ipomoea, Hippeastrum (amaryllis) and Brugmansia.
Cup/saucer
Highly attractive to pollinators, cup, bowl and shallower saucer-shaped blooms have an open form that creates a soft, relaxed feel in a planting. Examples include Eschscholzia californica, Oreomecon nudicaulis (Icelandic poppy), Geranium, Papaver, Tulipa, species roses, Geum, Magnolia, Crocus, Paeonia, Ranunculus, Anemone, Potentilla, Cistus and Oenothera (evening primrose).
Daisy
Daisy, rounded and star-shaped forms, with their irresistibly cheery faces, really help bring
a planting together. What appears as a single flower is often actually a composite of many tiny flowers arranged on a central base. Examples include Helenium, Echinacea, Helianthus (sunflowers), Cosmos, Symphyotrichum (asters), Rudbeckia, Erigeron, Astrantia, Chrysanthemum and Leucanthemum.
Bells
Bell and funnel-shaped flowers are charming with their nodding or pendent, down-facing flowers. Whether individual bells, such as fritillaries, or multiples arranged on a spire, such as foxgloves, they are often attractive to bees, as they provide easy or specialised access to nectar stores. Examples include Fritillaria, Campanula, Digitalis, Fuchsia, Hyacinthoides non-scripta (bluebell) and Convallaria majalis (lily of the valley).
How to combine flower shapes for maximum impact
• Think contrast Combine spikes or vertical flowerheads with rounded ones, and rounded ones with umbellifers or airy forms for the most impact. Use a mix of large, medium and small-sized flowers too, and those with clustered flowerheads alongside single blooms.
• Layer up Try diverse flower shapes at varied heights throughout the scheme, low and high, to create dynamism.
• Pick your A-team Contrast is good, but to ensure a feeling of easy harmony, avoid using too many different shapes together.
• A big bouquet Take some insights from floral designers when laying out, such as starting with the largest flowers, filling with smaller ones and using medium-sized blooms as the bridge between them. You need to try to balance the ‘visual weight’ of each element.
• On repeat As with colour in a border, repetition of flower forms at intervals creates a sense of rhythm and cohesion.