How To Add Height To Your Herbaceous Border

Add another dimension to your border with a small tree or tall flower spire

Herbaceous borders can look a bit flat without undulations in height and focal points to lead the eye. Height can be achieved in several ways but the crucial question you have to ask yourself is what do you want the final result to look like. If you want to inject some formality into the planting scheme why not go for classical statuary or a well-spaced row of sculptural trees. The trees could take the form of tall slim Mediterranean cypress, tightly clipped topiary box or a standard formal ‘lollipop’ shape. The ‘lollipop’ standard trees are now available in a wide range of evergreen and deciduous trees and of course the popular rose. A row of decorative wrought iron obelisks without anything growing up them would also provide a touch of structure and formality. Try growing just foliage climbers up obelisks and keeping them trimmed to form a topiary-like focal point.

If you want to maintain the loose informal look you could go for willow obelisks or rustic sculptures in rusting metal or again in willow. A bird bath will inject life into the border, and the birds which visit it should also act as pest control by feasting on nuisance insects, such as aphids. A selection of tall plants will add height but keep the border looking informal. The plants can be tall spires, majestic and sculptural or soft and relaxed. Obelisks softened by climbers and placed at regular intervals along the border will lead the eye down the whole border.

Acer at Lakeland Horticultural Society, Holehird

Small loose-limbed deciduous trees which let through dappled sunlight can be incorporated in a large border. These can be under planted with spring herbaceous plants such as: primroses, violets, hellebores and wood anemones to extend the season of interest in what is essentially a blast of summer colour in an herbaceous border. Grow some smaller perennials, which don’t mind dappled shade, underneath the trees; keep the lowest branches fairly high to allow as much light as possible through.

If you want to stand out from the crowd why not incorporate something a little different into your borders. Try growing climbing beans up the obelisks or use Globe Artichokes (Cynara scolymus) or Cardoons (Cynara cardunculus) as a statement piece. They produce up to 12 thistle-like flowers; if you want to eat the Artichoke harvest it before it flowers. Climbing  beans have either red or white flowers with the added attraction of having delicious beans to harvest from mid-summer. Try ‘Purple Cascade’ for attractive long purple pods or ‘Solista’ for mottled red/white pods.

Agapanthus 'Midnight Star'

There are always the tall stately plants which stand head and shoulders above the rest; they come in tall slim spires, for example Eremurus (Foxtail Lily) or explode in a ball of colour, such as Agapanthus. If you like the sculptural aspect of huge tropical leaves go for Cannas or a Banana. There are also the small delicate frothy flowers of Crambe cordifolia or the waving grass of Stipa gigantea.

Small deciduous trees for the border:

Acers (Japanese Maples); there is a huge variety and leaf colour of these slow-growing ornamental trees. Avoid the dissectum weeping types as they don’t allow for any under-planting and cannot be pruned. Acer shirasawanum ‘Aureum’ has fantastic yellow/lime leaves throughout summer and scarlet red keys in autumn. Acer palmatum ‘Senkaki’ (Sango Kaku) is the most gorgeous Acer with bright red stems and leaves which start out lime green in spring turning darker as summer progresses and ending up brilliant red/orange in autumn. These Japanese maples won’t tolerate winds or the midday sun as their leaves will scorch, so make sure they are planted somewhere sheltered and where they only receive the early morning or late afternoon sun.

Acer shirasawanum ‘Aureum’

Albizia julibrissin ‘Summer Chocolate’ (Silk Tree) has lovely ferny, finely cut foliage in a purple/chocolate colour and pink fluffy flowers in late spring. Unfortunately it is not hardy so needs a frost free south facing position in moist well-draining soil. If you live in a cold area plant it in a container and sink it in the border then take it indoors into a frost-free environment over winter. It reaches a height of 9m (30’) and a spread of 4m (13’) after 50 years but can be pruned in late winter/early spring to keep it compact.

Cornus controversa ‘Variegata’ (Wedding Cake Tree) is a lovely tiered small tree with green leaves edged with cream which turn reddish purple in autumn. It has small sprays of creamy white flowers in June. It is slow growing reaching a height and spread of 4 – 8m (13 – 26’) after 50 years. It needs a position in full sun or dappled shade in a moist, deep fertile soil.

Cornus controversa ‘Variegata’ (Wedding Cake Tree)

Cornus kousa ‘China Girl’ is a dogwood with large creamy white bracts in June followed in autumn by pink strawberry-like fruits, especially after a hot summer. It needs to be planted in fertile well-draining soil in full sun or partial shade. It is fairly slow growing, eventually reaching a height of 6m (20’) and a spread of 5m (16’) after 50 years. The previous summers weather affects the flowering, it really needs a long hot summer to flower at its best, a cool damp summer will produce a poor show the following year. Cornus kousa ‘Miss Satomi’ is a dark pink form.

Corylus avellana ‘Contorta’ is a slow growing hazel with corkscrew branches which add a sculptural element to the winter garden. It has golden yellow catkins in February/March. It needs a position in full sun or partial shade in fertile well-draining soil and needs very little maintenance, just take out any dead branches in spring.

Magnolia ‘Pink Beauty’ can be grown as a standard, height 150 – 200cm (60 -80”) and spread 90cm (36”), so is ideal for a small border. It has large goblet shaped pink flowers in spring, which can be spoiled by a late frost so it is best grown in a sheltered position in full sun or partial shade. It needs a well-drained moist acid soil so incorporate some ericaceous compost when planting.

Sculptural trees:

Buxus (Common Box) can be kept under control by clipping and is readily available in garden centres in the shape of a spiral, cone, ball or square. It requires a light, moisture retentive, well-drained soil in full sun or partial shade. The only problem is its susceptibility to box blight, so if you have already had this disease then it is not recommended to plant box, maybe plant something similar which can also be trained, such as Ligustrum (Privet) or Taxus (Yew).

Chamaeycparis lawsoniana ‘Columnaris’ (False Cypress) is a narrow conifer with blue foliage which will reach a height of 1.5 – 2m (5 – 6.5’) after 10 years but its eventual height could be 12m (39’) so it is not a tree for a small border unless you want to replace it every 10 years. It will tolerate some clipping but cutting the top to restrict its height could result in spoiling its shape. It requires a well-drained sunny position.

Cupressus sempervirens ‘Stricta’ (Italian Cypress) is a dark green conifer for the large garden, unless you want to replace it every few years. Again it can reach a height of 12m (39’). It also needs a well-drained sunny position.

Juniperus communis ‘Hibernica’ (Irish Juniper) is a conifer which does not grow as tall as the previous two conifers, reaching a height of 2 – 3m (6.5 – 10’) after 10 years. Eventually it will reach a height of 4m (13’). Again it needs a sunny well-drained position.

Juniperus ‘Skyrocket’ is a very tall slim conifer which eventually reaches a height of 5m (16’).

Taxus baccata is the traditional Yew which can be clipped to shape. ‘Fastigiata’ (Irish Yew) is a slim variety of the common yew which requires no clipping and only reaches a height of 3m (10’). It also comes in a gold form and one with green leaves with a gold edge. The common yew grows very slowly and can be clipped to shape so it need never get out of hand. It needs fertile, well-drained soil in full sun.

Perennials for growing in dappled shade:

Astrantia flowers from May to August and comes in a good range of colours; wine, pinks and white. ‘Hadspen Blood’ is a good dark wine.

Astrantia 'Hadspen Blood'

Anemone (Japanese); these flower later in the season from August to September and come in a range of pinks and white. ‘Honorine Joubert’ is a gorgeous pure white with dark yellow stamens.

Anemone nemorosa is the small white woodland anemone which flowers in spring.

Brunnera macrophylla looks like a large version of the blue Forget-me-not with silvery leaves. It flowers from March to April and forms a large clump. ‘Jack Frost’ is a particularly good cultivar.

Dicentra eximia ‘Snowdrift’ is a lovely small white form of the common Bleeding Heart which flowers from April to July, eventually forming a large clump.

Geranium ‘Anne Folkard’ is a good clear magenta which flowers throughout summer and will straggle through other plants.

Geranium macrorrhizum is a reliable clump forming perennial available in many colours from white through to dark, dusky pink. ‘Bevans’ is dark pink and flowers from June to July; if it is cut back immediately after flowering you will often get a second flush of flowers in late summer. It has the added bonus of having fragrant foliage which turns scarlet in autumn. ‘Pindus’ is a low growing ground covering variety with dark pink flowers.

Geranium magnificum ‘Rosemoor’ is a good strong blue which has one flush of flowers in June/July but if it is cut back as soon as it has flowered it will flower again in late summer.

Hostas come in many varied forms from just a couple of centimetres tall to nearly a metre and in a range of leaf colours from blue to green with white and cream margins. They are mainly grown for their foliage but they do have fairly insignificant pale lilac or white flowers.

Hosta and Allium at Lakeland Horticultural Society, Holehird

Pulmonaria (Lungwort) ‘Sissinghurst White’ has lovely spotted leaves and good clear white flowers; flowering in March to May it lightens up dappled shade.

Tricyrtis formosana (Toad Lily) ‘Dark Beauty’ has an unusual spotted blue flower. It flowers from August to September.

Tall plants:

Cannas are invaluable for their architectural leaves but unfortunately are not hardy so will need to be brought into a frost free environment over winter. Start them growing indoors in early spring then plant them into the border at the beginning of June. Depending upon variety they can grow to over 180cm (6’). The flowers are available in all the hot colours from pale lemon to the hottest red or they can be grown for their leaf colour which ranges from green to purple to striped.

Crambe cordifolia (Greater Sea Kale) is a large perennial with a frothy mass of white scented flowers in June and July; reaching a height of 3m (10’) and spread of 1.5m (5’). It needs to be in full sun and sheltered from strong winds in a moist, fertile, well-draining soil.

Delphiniums are the quintessential border plant for a cottage garden feel. They produce a fantastic spire of closely packed blooms with some varieties reaching a height of 180cm (6’). They come in a variety of colours: pink, peach, white and a huge array of blues. They are greedy plants so make sure they have plenty of organic matter incorporated in the planting hole and feed well throughout the season. They need a position in full sun otherwise the flower spikes may be small and weak. It is essential to stake them as they easily snap in the wind. Slugs see them as a five star restaurant so you must protect them as soon as they emerge after winter.

Delphinium 'Coral Sunset'

Eremurus (Foxtail Lily) is a huge spectacular spire of tiny star-shaped flowers, normally reaching a height of 210cm (7’) but robustus has been recorded reaching a height of 3m (10’). They come in a range of colours: yellow, orange, white and pink. They need a position sheltered from strong winds in full sun and well-drained soil.

Kniphofia (Red-hot Pokers) are another cottage garden favourite which produce a tall spike of flowers, up to 150cm (5’), in late summer in a range of hot colours from pale lemon to orange and red. They are easy to grow in full sun or partial shade in moist, well-drained, fertile soil.

Lilies come in a huge array of colours and sizes but one of the most spectacular is the Tree Lily which can reach a height of 2.5m (8’) and a spread of 60cm (24”). They need a sunny sheltered site with moist, fertile, well-draining soil. Once they have become established over the years one bulb can produce up to 30 single blooms. One to try is ‘Pink Explosion’ which produces a huge number of beautifully scented blooms.

Lupins are another essential cottage garden plant coming in a huge palette of single and bi-colours. Like delphiniums they need a moist, fertile, well-draining soil in full sun but they do not need staking. Unfortunately they are also a five star slug restaurant.

West Country lupins

Stipa gigantea (Golden Oat Grass; Giant Feather Grass) is a lovely addition to any border producing a huge fan-shaped spray of feathery golden seed heads in June to July. It makes a large clump growing to a height of 240cm (8’). It needs well-drained moist soil in full sun.