Plants that add light height to a planting scheme are the magic ingredients. They lift heavier and more solid subjects, they veil and reveal and can change perspective according to the line of sight. They may add vertical lines, or clouds of soft lace; some have small flowers and delicate stems, others have finely cut leaves and slender branches. Perennials and annuals that drift through a planting scheme with little regard to the height of their neighbours fit the bill perfectly. The trend seems to be for designers to use more and more of these light, airy subjects in their planting schemes.
Anthriscus sylvestris 'Ravenswing' a dark leaved and dark stemmed form of cow parsley introduces lacy clouds of soft white in early summer. The effect may not be enduring, but that is part of the magic. It adds a different dimension for a few weeks, then allows other subjects to have their turn.
Alchemica mollis has a similar effect at a lower level. Lady's mantle seeds and spreads freely to the annoyance of some and delight of others. Its lime green frothy flowers are the perfect complement to any other colour and unlike many other subjects in its class it makes excellent ground cover. Avoid planting alchemilla too close to the front of the border where it can spill onto the lawn and become a nuisance; plant if further back and allow it to erupt amongst other plants. To prevent spread shear the plants back as the flowers turn from lime to ochre.
The bronze-leaved form of fennel, Foeniculum vulgare is one of my favourite drifters. The finely cut foliage adds smoky clouds to the planting which develop into high stems carrying filigree flower heads of soft yellow. Allow it to plant itself at the front of the border and look through it. It is perfect on poor soils and in dry conditions.
Fennel is just one of a number of umbellifers becoming very trendy with garden designers. On a larger, bolder scale Angelica archangelica and Angelica gigas are stunning biennials that become perennial subjects in the garden by self-seeding. They have the benefit of architectural foliage and see-through flower heads.
The best of the tall herbaceous perennials
The scabious-like Knautia macedonica is a lovely light perennial that will drift and seed as it pleases if it likes your soil. Generally poor, light soils are best for self- seeding. The fine stems can tower to 1.5 metres (5ft) or so. In my garden the seedlings always seem to establish most successfully near the edges of the planting. Sometimes I transplant them but usually I leave them, bees and butterflies enjoy their presence as much as we do.
On a larger scale the soft green flowered Cephalaria gigantea is a useful plant to add light height and vertical lines in the centre of a bed or further back in the border, It can easily grow to 1.8metres (6ft) or more and although strong it will need support from its neighbours or twigs or other supports put into position earlier in the season. It is particularly useful amongst taller shrub roses.
Digitalis, foxgloves are nothing new in the designer's palette. One that I am surprised had not become more trendy is the lovely Digitalis lutea. This is a small perennial variety with fine spikes of delicate tubular flowers of soft green. It is brilliant towards the front of the border and works with any other colour. It will seed and drift randomly if you let it and it is often seen amongst roses and perennials in established summer gardens.
It is a lovely contrast to the light airy presence of Nepeta 'Six Hills Giant' the soft lavender-blue flowers are amazingly attractive to bees and butterflies for many weeks, if not months during the summer. I find this perennial is much more successful with a grow-through plant support in place from late spring. If placed 20cm, 8" above the ground the grid will lend that gently support at the base of the stems without compromising the natural lightness of the plant.
For light height of a very different form Iris sibirica 'Flight of Butterflies' is another designer's choice. Iris sibirica has the advantage of slender upright, grass-like leaves that stay looking good for so much longer than the flag irises. It is also a clump-forming perennial which needs less maintenance and can cope with competition. Slender upright stems carry delicate sapphire blooms in early summer; a plant that lives up to its name.
If it was easier to establish the white willow herb, Chaemerion angustifolium ‘Album’ would undoubtedly be the designer’s choice. Its sparkling white airy spikes rise high above its neighbours and it is a marvellous drifter. It produces little fertile seed and seems to resent transplanting and growing in a pot. It therefore remains aloof and resistant to wider planting. Definitely worth persevering with as a garden plant
Other recommended plants to add light height to a planting scheme:
Centranthus ruber ‘Albus’