Seedheads rarely have much to offer in the way of colour, at least in comparison with flowers or even foliage. Instead, their aesthetic qualities are best appreciated through their form, so it is useful to begin with some basic categories and concepts which will help our approach to understanding and using the beauty of seedheads in the garden.
A number of basic shapes appear and reappear in the world of the seedhead. To a large extent they reflect the shape of the inflorescence from which they are derived. The following classification of shapes owes much to Piet Oudolf.
Single seeds Occasionally, individual seeds or their immediate supporting structures are large enough to make a visual impact, as with the annual Atriplex hortensis var. rubra, whose large grain-like heads are clearly visible, or the bunches of winged seeds of maples. All types of grasses fall into this category.
Single heads and pods Some individual seedheads are large enough to dominate our impression of a plant, whether they are single or in bunches. The big upright pointed cases of many members of the Apocynaceae, such as Asclepias, or the bean-like pods of the Fabaceae are good examples. Such seedheads have a strong and somewhat definite look about them and tend to be visually arresting. Lighter, feathery seedheads make a good visual contrast.
Spikes Although plants which carry their flowers and seedheads on tall stems to form spikes or spires are relatively few, they are invaluable for structural effect, particularly during winter. They include many Scrophulariaceae such as verbascums. The repetition of spikes across a space can be one of the most visually arresting features in perennial planting. Many seedheads form less immediately noticeable spikes, or at least upright heads. While these tend to have less impact, they are useful for the sense of structure they create.
Umbels Such seedheads are gathered into rounded structures, which can vary from practically flat-topped in the case of Achillea filipendulina to very rounded in the case of Angelica gigas. The flatter ones (as most are) contrast effectively with spires, with the horizontal balancing the vertical. Massed umbels, as with Sedum spectabile hybrids or Achillea hybrids, can be striking, but lack the impact of massed spikes.
Globes Relatively few seedheads form globes, but the ones that do are invaluable, loved by both gardeners and flower-arrangers. We seem to take particular delight in those that form near-perfect spheres, such as certain alliums.
Panicles Loose structures with seedheads in multi-branched heads are often not particularly dramatic unless either launched skywards on tall stems or particularly finely feathery, as with some grasses. In many cases they may have a decorative vagueness, and sometimes even a see-through quality, as with many cultivars of the grass Molinia caerulea.
Buttons Those members of the Asteraceae and others which have their flowers and then their seeds closely packed into tight heads, such as Centaurea, are often useful for contrasting with wispy panicles. Tight points of definition are especially useful in wildflower meadows, as all around them tends to appear loose and chaotic.
Whorls Whorls of seedheads arranged around an upright stem give an impression of order and design, and can be very effective if repeated across a space. The more tightly the individual seedheads are packed, the greater the feeling of definition.